Body Representation in Children and Adolescents

by

Sandra Marie Pacione

A thesis submitted in conformity with the requirements for the degree of Master of Science

Exercise Science University of Toronto

© Copyright by Sandra Marie Pacione 2015

ii

Body Representation in Children and Adolescents

Sandra Marie Pacione

Master of Science

Graduate Department of Exercise Science

University of Toronto

2015

Abstract

The purpose of the present study was to determine if children and adolescents are able to

map the body parts of other children and adolescents on to the representation of their own body

parts and if age influences this mapping. To this end, participants completed a body-part

compatibility task where responses were executed to coloured targets (relevant feature) presented

over the hand or foot (irrelevant feature) of separate male models of different ages (7, 11, and 15

years of age). It was found that body-part compatibility effects emerged for both the 10-12 and

13-16 year old age groups. No body-part compatibility effects were found for the 7-9 year old

age group. Most interestingly, the body-part compatibility effects for both the 10-12 and 13-16

year old age groups occurred when viewing models of their own peers. Overall, the results

indicate that the body-part matching process is sensitive to social factors.

iii

Acknowledgments

I would like to express my deepest gratitude to my supervisor, Professor Timothy Welsh,

whose unwavering support and understanding helped enrich my graduate education and fueled

my passion for research. To my committee members, Professor Luc Tremblay and Doctor Jessica

Brian, I am extremely grateful for your support and suggestions throughout the project. To my

lab mates, thank you for your encouragement and daily dose of laughter. To my friends and

family, thank you for helping me to succeed throughout the years. Most of all, I am fully

indebted to my parents, for their understanding, patience, and encouragement and for pushing me

farther than I thought I could go.

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Table of Contents

Acknowledgments ........................................................................................................................ iii

Table of Contents ......................................................................................................................... iv

List of Tables ................................................................................................................................ vi

List of Figures .............................................................................................................................. vii

Introduction .................................................................................................................................. ix

Chapter 1 Literature Review ....................................................................................................... 1

1.1 Introduction ......................................................................................................................... 1

1.2 Perception-Action Coupling ............................................................................................... 1

1.2.1 Summary ................................................................................................................. 4

1.3 Self-Other Mapping in Action and Shared Experiences ..................................................... 4

1.3.1 Self-Other Mapping and Action Observation in Children ...................................... 7

1.3.2 Summary ................................................................................................................. 8

1.4 Body Schema ...................................................................................................................... 9

1.4.1 Body Schema Development .................................................................................. 11

1.4.2 Summary ............................................................................................................... 12

1.5 Body-Part Compatibility ................................................................................................... 12

1.5.1 Summary ............................................................................................................... 15

1.6 Conclusion ........................................................................................................................ 16

1.7 The Current Project: Purpose and Specific Hypotheses ................................................... 17

Chapter 2 Research Article ........................................................................................................ 19

2.1 Introduction ....................................................................................................................... 19

2.2 Methods ............................................................................................................................. 22

2.2.1 Participants ............................................................................................................ 22

2.2.2 Apparatus, Task, and Procedure ........................................................................... 22

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2.3 Results ............................................................................................................................... 26

2.3.1 Spatial Compatibility ............................................................................................ 26

2.3.2 Body-Part Compatibility ....................................................................................... 28

2.3.3 Correlation of Upper and Lower Spatial RTs with Body-Part RTs ...................... 33

2.4 Discussion ......................................................................................................................... 35

Chapter 3 General Discussion .................................................................................................... 39

3.1 Findings and Implications ................................................................................................. 39

3.2 Limitations ........................................................................................................................ 41

3.3 Future Directions .............................................................................................................. 45

3.4 Delimitations ..................................................................................................................... 47

Chapter 4 Conclusion ................................................................................................................. 48

References .................................................................................................................................... 50

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List of Tables

Table

Number

Table Caption Page

Number

Table 2.1. Mean (and standard deviations) of the % of response errors as a

function of Presentation Side, Responding Effector, and Spatial

Height.

27

Table 2.2 Mean (and standard deviations) of the % of response errors as a

function of Presentation Side, Responding Effector, Model Type,

Target Location.

28

Table 2.3. Mean (and standard deviation) response times in milliseconds for

each of the 3 Groups as a function of Model Type and Target

Location. Marginal means are also provided.

29

Table 2.4. Planned comparison of response time differences across the three

age groups.

29

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List of Figures

Figure

Number

Figure Caption Page

Number

Figure 2.1. Examples of the 7, 11, and 15 year old models with coloured targets.

Only a single image was presented on each trial. The black boxes

surrounding each image were not presented in the experiment, but were

included here to demonstrate the different sizes and proportions of the

images.

24

Figure 2.2. Examples of the coloured targets in lower and upper space. The black

boxes surrounding each image were not presented in the experiment,

but were included here to demonstrate the different locations of the

targets in the trials.

25

Figure 2.3. Mean response time in milliseconds for the 7 to 9 year old group as a

function of model type and target location. Standard error of the mean

bars are depicted. Note that the response time scale is consistent across

Figures 2.3, 2.4, 2.5 at 200ms, although the range over which the data

are depicted are different.

31

Figure 2.4. Mean response time in milliseconds for the 10 to 12 year old group as a

function of model type and target location. Standard error of the mean

bars are depicted. Asterisks indicate significant difference between

target locations, p <.05 *.

32

Figure 2.5. Mean response time in milliseconds for the 13 to 16 year old group as a

function of model type and target location. Standard error of the mean

bars are depicted. Asterisks indicate significant difference between

target locations, p <.05 *.

33

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Figure 2.6. Correlation of body-part difference scores from the body-part

compatibility task (y-axis) as a function of the spatial difference scores

from the spatial compatibility task (x-axis) for the 7 to 9 year old

group.

34

Figure 2.7. Correlation of body-part difference scores from the body-part

compatibility task (y-axis) as a function of the spatial difference scores

from the spatial compatibility task (x-axis) for the 10 to 12 year old

group.

34

Figure 2.8. Correlation of body-part difference scores from the body-part

compatibility task (y-axis) as a function of the spatial difference scores

from the spatial compatibility task (x-axis) for the 13 to 16 year old

group.

35

Figure 3.1 Difference scores of the incompatible by compatible conditions as a

function of model type for the 7 to 9 year old group. Conference

Intervals are depicted. Black dots indicate the three 7 year old

participants’ scores.

42

Figure 3.2 Difference scores of the incompatible by compatible conditions as a

function of model type for the 10 to 12 year old group. Conference

Intervals are depicted.

43

Figure 3.3 Difference scores of the incompatible by compatible conditions as a

function of model type for the 13 to 16 year old group. Conference

Intervals are depicted.

43

ix

Introduction

In daily life, humans are constantly interacting with other people - be it helping an elderly

woman carry her groceries or talking with neighbours. According to Hobson and colleagues, to

identify with someone else is to relate to the actions of someone else from the other person’s

perspective. Through this identification process, it is possible to share experiences of the world

with another individual from the other’s perspective (Hobson & Hobson, 2007; Hobson & Lee,

1999; Hobson & Meyer, 2005). One of the processes that are thought to facilitate this complex

ability of identification and social interaction is one in which humans register the perceptions and

thoughts of others against the neural representations used to perceive the self. The main premise

of this theory is that an understanding of others occurs through the use of self-representations

(Lombardo et al., 2010). These cognitive representations of the self and the other are thought to

be fundamentally grounded in the physical context of the body (Niedenthal, Barsalou,

Winkielman, Krauth-Gruber & Ric, 2005). To perceive and act in its environment, the

individual’s body and its interactions with the sensory and social environment are represented in

the brain. Internal representations of the body are closely tied to the processing of action

understanding and social interactions, and hence social cognitive processes (Assainte, Barlaam,

Cignetti, & Vaugoyeau, 2014; Niedenthal et al., 2005).

The purpose of the present research is to investigate the integrity of mechanisms

underlying the ability to represent the bodies of other humans (i.e., self-other matching) in

typically developing (TD) children and adolescents. To investigate these processes, I will

evaluate the performance of TD individuals using a human body-part compatibility task (e.g.,

Bach, Peatfield, & Tipper, 2007; Welsh, McDougall, & Paulson et al., 2014; Pacione & Welsh.,

in press), which provides an index of the body-part matching process. Specifically, participants

will respond to coloured targets (relevant feature) presented over the hand or foot (irrelevant

feature) of separate male models of different ages (7, 11, and 15 years of age). The information

generated by the present study can be used to understand the neural underpinnings of how one’s

own body position influences one’s perception of others’ body representations.

My general predictions are that if the bodies in the images are mapped onto the human

body schema of the observer, then a body-part compatibility effect will be observed (as in Bach

et al., 2007; Welsh et al., 2014; Pacione & Welsh, in press). If the bodies in the images are not

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mapped onto the human body schema of the observer, then no body part compatibility effects

will be observed and there will be no differences between response times (RT) to stimuli

presented on the different body parts. With respect to the main research question, it is further

predicted that if the individuals of different ages are able to map the bodies of all the images onto

the human body schema, then generalized body-part compatibility effects will be observed across

all age groups. Alternatively, if the individuals are able to map the bodies of age-related images

onto the human body schema, then age-specific body-part compatibility effects will be observed

(as in Bach et al., 2007; Welsh et al., 2014; Pacione & Welsh, in press).

In the present document, I will begin by reviewing the theoretical underpinnings of both

perception-action coupling and self-other matching, followed by a discussion on the body

schema and finally, examine the role of body-part compatibility. This literature review will be

presented in Chapter 1. In Chapter 2, I will present my experimental findings associated with the

research question. In Chapter 3, I will discuss the implications of the research findings, followed

by a discussion of the current design of the experiment and applications for future research.

Finally, in Chapter 4 I will conclude with a summary of the purpose and main research findings

of the presented work and review some of theoretical underpinnings.

1

Chapter 1 Literature Review

1.1 Introduction

Humans have an inherent ability to understand other people. The ability to understand

others may be fundamentally situated in distributed neural networks that encompass shared self-

other body and action representations. This network is thought to enable individuals to represent

their own and others’ goal-directed actions via a single conceptual system (Decety &

Sommerville, 2003). This conceptual system would allow individuals to understand the actions,

emotions, and intentions of others. This innate relationship between the self and the other has

been recently underlined by theories of embodied cognition according to which bodily

experiences play a primary role in human cognition - cognitive processes are essentially

grounded in bodily states (Gallese & Sinigaglia, 2011). The notion of embodiment implies that

individuals draw on information from their own experiences and action capabilities to interpret

their environment and shape their own cognitive processes. Such experiences, however, are also

likely to be involved in the ability to perceive and to know the structure and movements of the

bodies of other individuals, and ultimately, to understand their actions and to interpret their

gestures for social communication.

In this review, I will begin with a discussion of perception-action coupling, followed by a

review of self-other matching in action and shared experiences. The review of this literature will

highlight why the action-perception coupling mechanism offers a functional bridge between

actions produced by the self and those produced by others, grounded on self-other equivalence. I

will also review recent neurophysiological evidence on the body schema and conclude with a

section on body-part compatibility. This latter literature will explore why the body-part

compatibility task appears to be an effective tool to assess self-other matching and potentially,

the involvement of the human body schema in social cognitive processes and will provide the

direct theoretical context for the present investigation.

1.2 Perception-Action Coupling

Not only are individuals able to select, plan and execute a variety of actions to achieve

their own personal goals, but individuals are also able to perceive and predict the intended and

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expected effects of such actions. The continuity between action and perception is thought to be

formed on the basis of an ideomotor (or common coding) network. In this common coding

network, the neural codes that are responsible for generating specific goal-directed action are

tightly coupled to the codes that represent the perceptual consequences of those actions

(Hommel, 2009; Prinz, 1997). It is thought that by repeatedly performing a movement and

experiencing the perceptual consequences of that action, a bidirectional association is formed

between the neural codes that represent the motor pattern that was generated and the sensory

consequences that action produced. The result of this bidirectional binding is that the activation

of one code can result in the activation of the other. That is, this bound action-effect coding

enables individuals to not only react to the environment by selecting the most appropriate effects

for a given situation, but also to anticipate the consequences of one’s own actions and the actions

of others. This series of coupled activation is thought to facilitate efficient and accurate response

selection (Elsner & Hommel, 2001).

Elsner and Hommel (2001) demonstrated action-effect integration through experience

across a series of studies. During the training phase of one task, they had participants perform a

choice reaction time task in which they made arbitrary left and right keyboard presses. A specific

effect tone followed each response, specifically, a high tone would follow a left key press and a

low tone followed a right key press. It was predicted that the constant pairing of a response with

an effect tone would lead to binding between that specific response and a specific tone.

Following the training, subjects were presented with a free-choice task where one of the two

effect tones was randomly presented prior to the moment at which the participant was to choose

to execute a left or right key press. The critical finding of the studies was that participants were

more likely to choose and execute the response that was compatible with effect tone that was

presented as the task-irrelevant pre-cue tone. That is, left key responses were made more often

after a high tone than when a low tone was presented, and right key responses were made more

often following a low tone than after a high tone. The authors concluded that this finding

indicated that participants formed an association between the motor pattern underlying the action

and the perceptual consequence of the action effect through experience during the training phase,

and that the presentation of the effect tone in the testing phase (e.g., a high tone) activated the

response code that would lead to that effect (e.g., left response). This pre-activation of the given

response then biased response selection processes leading to the more common execution of the

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response that was associated with the effect tone presented as the pre-cue. Overall, these findings

lend considerable support for a bidirectional relationship between actions and their perceptual

effects.

Relatedly, other researchers have proposed that individuals use a forward model to

predict their own actions as well as the actions of others (Wolpert, Ghahramani, & Jordan, 1995;

Wolpert, 1997, Blakemore & Decety, 2001). According to this approach, during self-produced

actions, a sensory prediction of the outcome of the action is produced along with the actual

motor command. The forward model makes a prediction of the sensory consequences of motor

commands, which are compared with the actual consequences of the movement. The results of

the comparison between the sensory prediction and the sensory consequences of the act can then

be utilized to reconfigure afferent inputs to bring about the desired action.

Although not yet directly linked to the forward model or ideomotor theory, the discovery

of ‘mirror neurons’ provided the first convincing physiological evidence for a direct link

between action perception and action execution. It was reported by di Pellegrino and colleagues

(1992) that action-coding neurons or ‘mirror neurons’ reside in the prefrontal cortex of monkeys.

Surprisingly, these neurons discharged significantly more both when the monkey performed a

goal-directed action and when it observed another individual performing the same action.

Similarly, in humans, several brain regions including the premotor cortex, the posterior or

parietal cortex and the cerebellum, are activated both during action generation and while

observing and simulating others’ actions (Decety, et al., 1994; Decety et al., 1997; Ruby &

Decety, 2001; Fadiga, Fogassi, Pavesi, & Rizzolatti, 1995; Hari, Forss, Avikainen, Kirveskari,

Salenius, & Rizzolatti, 1998; Buccino et al., 2001). Thus, simply watching the goal-directed

movements of the body parts of another individual activates the same functionally specific

regions of the premotor cortex as performing those movements; a phenomenon sometimes

known as “motor resonance”.

In human subjects, a number of functional imaging studies have demonstrated the

involvement of motor representations during the perception of actions performed by others

(Hamzei, Rijntjes, Dettmers, Glauche, Weiller, & Buchel, 2003; Calvo-Merino, Glaser, Grezes,

Passingham, & Haggard, 2005). Notably, Buccino and colleagues (2001) showed that the

activation pattern in the premotor cortex elicited by the observation of actions performed by

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another individual follows somatotopic organization in conjunction with the observed action.

Specifically, they reported that watching mouth, foot, and hand actions elicits different activation

sites in the premotor and parietal cortices, which are normally involved in the actual execution of

the observed actions. These results strongly support the existence of an action execution-

observation matching system. This system would support the processes that allow individuals to

recognize actions performed by others by mapping the observed action on the individual’s own

motor representation. According to this hypothesis, action observation automatically activates in

the observer the same neural substrates involved in the actual execution of the observed action.

The activation of the same neural substrates during action observation would allow the observer,

through an execution-observation matching mechanism, to understand the perceived actions of

the other (Buccino et al., 2004; Decety & Grezes, 2006). This matching mechanism may provide

the basis for social interactions and constitute a necessary precursor for the capacity to imitate

and language acquisition (Rizzolatti & Arbib, 1998; Rizzolatti, Fadiga, Fogassi, & Gallese,

2002).

1.2.1 Summary

Action observation is thought to arise from action-perception coupling mechanisms that

are mediated by internal representations of the action themselves. In this common coding

network, the neural codes that are responsible for generating specific goal-directed action are

tightly coupled to the codes that represent the perceptual consequences of those actions

(Hommel, 2009; Prinz, 1997). This tight coupling and bidirectional activation enables

individuals not only to react to the environment, but also to anticipate the consequences of

others’ actions. Moreover, these representations not only guide behaviour, but may also be used

to interpret the behaviour of others. This action-perception coupling mechanism offers a

functional bridge between actions produced by the self and those produced by others, grounded

on self-other equivalence (Decety & Sommerville, 2003).

1.3 Self-Other Mapping in Action and Shared Experiences

Self-other mapping is a process by which individuals register the perceptions and

thoughts of others against the representations used to perceive the self. This process asserts that

the self and other are intricately tied together. Gallese (2001) emphasizes that to understand the

intended goals of an observed action, a link must be established between the observer and the

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observed actor. In doing so, the self is used as an anchor point for modelling others’ actions and

intentions (Lombardo et al., 2010). Specifically, individuals use information from their bodies

and action capabilities to understand the actions of others (Decety & Sommerville, 2003).

Consistent with ideomotor approaches, the sensory consequences of an individual’s

action can be used to understand and predict the actions of others (Jeannerod, 2001; Sebanz &

Knoblich, 2009; see also Wolpert, Ghahramani, & Jordan, 1995; Wolpert, 1997). According to

this model, during self-produced actions, a motor command and an efference copy (i.e., sensory

prediction) of the outcome are produced in parallel to predict the sensory consequences of the

motor act. The sensory prediction and actual sensory consequences are compared to better

inform future actions. Blakemore and Decety (2001) suggest that the forward model stores

representations of sensory predications associated with multiple actions. This store of predictions

of the consequences of self-generated actions could therefore be used to estimate the actions (and

therefore intentions) made by another individual. Thus, through an implicit process of action

simulation, the actions of another individual could be mapped onto the stored sensory predictions

of the individual’s own actions (Gallese, 2001; Blakemore & Decety, 2001; Jackson & Decety,

2004). This interpretation is also compatible with simulation theories, which assume that when

an individual observes the actions of others, one covertly simulates the same action (Jackson et

al., 2004). Observing the actions of another can therefore act as a mirror to gain more knowledge

about the self (Gallese, 2003).

The observation of action can initiate a simulated response in the observer (Blakemore &

Decety, 2001). Similarly, during situations involving more than one actor, action simulation can

also be used to coordinate actions with others. This process becomes clear when one considers

that joint action often requires that two or more individuals adapt their actions in time and space

to achieve a common goal (Sebanz & Knoblich, 2009; Sebanz, Knoblich & Prinz, 2003).

Critically, it is proposed that a shared task representation is created whereby co-actors attend to

the same objects and events, creating a ‘perceptual common ground’ (Sebanz, Bekkering &

Knoblich, 2006). For performance, it has been suggested that joint action coordination toward a

shared goal is to a large extent achieved by internal simulation of actions and effects that allows

co-actors to predict their own and their partner’s actions using their own motor system (Wolpert

et al., 2003). When coordinating actions with the other person, motor simulations of one’s own

and a partner’s actions need to be integrated to achieve a shared goal. This integration is

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achieved whereby the individual incorporates the others’ action capabilities into their own action

planning. Joint action provides a unique context by which the action capabilities of the self are

used not only to understand the actions of others, but are central to coordinating actions with

others.

At the neural level, it is interesting to note that our ability to represent our own thoughts

and actions and those of others are closely tied together and may share similar origins in the

brain (Decety et al., 2003; Jackson et al., 2004). Recent research indicates that the premotor,

insula and the right inferior parietal cortex may be crucial in correlating notions of the self with

the other. Activation of the right inferior parietal lobe correlates with sense of ownership in

action execution (Farrer, Franck, Georgieff, Firth, Decety, & Jeannerod, 2003). Similarly,

activation in the right inferior parietal lobe is also found in reciprocal imitation and during

mental simulation of another’s actions (Ruby & Decety, 2001). Additionally, when subjects are

asked to adopt another person’s perspective to evaluate their beliefs, the right inferior parietal

lobe is also strongly involved (Ruby & Decety, 2003). These findings highlight a partial overlap

between self-processing and the processing of others in the brain, lending support for a shared

neural representation (Jeannerod, 2003).

This shared neural representation goes beyond the domain of action to incorporate affect

and emotions, allowing individuals to empathize with others (Gallese, 2001, 2003). According to

Jeannerod (2003), empathy expresses the possibility that individuals are able to understand other

people’s behaviour because they attempt to replicate and simulate their mental activity. Such a

view has received empirical support from a variety of behavioural and neuroimaging studies that

highlight similar neural systems are involved both in the recognition and in the expression of

specific emotions. Dimberg and colleagues (2000) demonstrated that viewing facial expressions

triggers expressions on one’s own face, even in the absence of conscious recognition of the

stimulus. An fMRI study confirmed these results by showing that when participants are required

to observe or to imitate facial expressions of various emotions, increased neural activity is

detected in the regions that are implicated in the expression of these emotions, including the

superior temporal sulcus, the anterior insula, the amygdala and the premotor cortex (Carr,

Iacoboni, Dubeau, Mazziotta, & Lenzi, 2003). Similarly, the experience of pain by the self and

its observation in others also provides support for a shared neural representation of empathy. In

an fMRI study, Morrison and colleagues (2004) compared the activation pattern during the

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experience of pain and its observation in others. The results revealed common activated areas in

the anterior cingulate cortex and the anterior insula. Altogether, these findings emphasize a

system that prompts the self to resonate with the emotional state of the other through simulation.

Observing the other spontaneously activates the parallel motor representation and its associated

autonomic and somatic responses in the self.

1.3.1 Self-Other Mapping and Action Observation in Children

Observing the other and modelling one’s appearance and actions to more closely

resemble those of the one’s peers appears to be particularly relevant for pre-adolescent and

adolescent populations. Specifically, peer interactions at schools and community settings are

formally structured to facilitate same age interactions. Large amounts of time are spent with

peers of one’s own age, thus shaping shared experiences. These shared experiences are often

created through social play. Experiences gained within own-age groups foster similar behavioral

norms and interaction styles, and over time, these interactions may promote the development of

similar attitudes, motives, interests, and aspirations (Leaper, 1994; Maccoby, 1998). As such,

own-age peer groups represent a potentially powerful context for socialization (Serbin, Moller,

Gulko, Powlishta, & Colburne, 1994).

Social psychological research has demonstrated that children show preferences for

members of their own groups across many domains, including gender, race, and even nationality

(Bigler & Liben, 2006). Furthermore, there is social pressure to act in accord with one’s group.

Thus, children who do not conform to the social norms of the in-group are judged more harshly

than children who do, and this is especially true for older children and adolescents as compared

to younger children (Abrams, Rutland, Cameron, & Marques, 2003). In particular, peer

interactions may have both a positive and negative influence on child and adolescent

development. In particular, research has focused on the role of peers as socializers of

adolescents’ negative behaviours, such as drug use, smoking and delinquency (Brechwald &

Prinstein, 2011). Thus, children who share similar interests and commonalities may be viewed as

like-minded individuals and are perceived more positively. On the other hand, those children

who do not share commonalities with their own-age peers may be viewed as individuals who are

not ‘like me’ and excluded from the in-group. Subsequently, children may be biased in favour of

in-group members and will strive for consistency between themselves and their own-age peers

8

(Martin, Fabes, & Hanish, 2014). For instance, children want to be more like their own-age

group members which leads them to choose to interact with same-aged peers.

The limited amount of research that has been done on action observation and execution in

children reveals findings that are consistent with this own-age group affiliation effect. In

particular, Marshall and colleagues (2010) investigated motor contagion in children. Motor

contagion is an interference effect that occurs during movement execution when simultaneously

observing someone else’s incompatible action. The authors found stronger contagion effects

when children observed dynamic images of their own peer. Specifically, they instructed children

to move a stylus on a graphics tablet vertically or horizontally in the presence of a background

video. The background video was of a model moving her arm in a direction that was either

congruent or incongruent with the axis of the child’s stylus movements. The presence of the

incongruent background movements was associated with significant interference effects on

children’s stylus movements; there was more motion in the incongruent direction. Of particular

importance, this interference effect was stronger when the background movements were

performed by a same-aged peer rather than by an adult. Thus, these findings suggest that there

may be an age specific bias in motor resonance and, perhaps, body mapping with children and

adolescents.

1.3.2 Summary

The ability to engage with others is critically grounded in a shared neural representation

between the self and other. It is this shared self-other representation that allows individuals to

understand the behaviours, thoughts, and emotions of others. It is made possible through a

simulation mechanism that matches action observation and execution onto the same neural

substrate (Gallese, 2001). Self-other equivalence is particularly relevant for pre-adolescent and

adolescent populations. Specifically, children learn the ‘culture’ of their own-age group and they

subsequently seek to be viewed as like-minded individuals and be perceived more positively by

their own age peers. Ultimately, an individual’s capacity to share experiences with others is

fundamentally grounded in the body. Gallese (2003) suggests that what makes the behaviour of

other agents intelligible is the fact that their body is experienced as something analogous to one’s

own experienced body. This correspondence is achieved by identifying the body parts of others

9

and matching those to the representation of one’s own body parts in the brain – a process I turn

to next.

1.4 Body Schema

Perhaps some of the more compelling evidence for the existence of a cognitive

representation of body position comes from the earliest interactions between infants and their

adult models. It appears that even before experiencing contact with the environment, humans are

equipped with a rudimentary knowledge about the dynamic organization not only of one’s own

body, but also of its relations to other bodies. Even minutes after birth, infants show a strong

innate tendency to mimic sounds and oro-facial motor acts performed by the adult models in

front of them (Meltzoff & Moore, 1977). This finding indicates that infants can visually identify

the movement of a specific part of the adult body and produce a similar movement in the

corresponding part of their own anatomy (Berlucchi & Aglioti, 2010). This early form of

imitation is an example of the established link between the self and other.

Neuropsychological evidence for an individual’s ability to code body parts was initially

derived from studies that reveal that humans possess a body schema or a mental construct

devoted to the dynamic spatial organization amongst parts of the body of the self and its relations

to that of other bodies (Semenza & Goodglass, 1985; Semenza, 1988; Ogden, 1985; Sirigu,

Grafman, Bressler, & Sunderland, 1991). It is thought that a body representation (or schema) is

used for the unconscious encoding of body position for both the self and others because it is

evoked during the perception of a human body. For example, Reed and Farah (1995) had

participants perform a series of same-different visual matching tasks for body position memory.

Specifically, participants had to determine if the cued position of a human model had changed or

not. At the same time, participants engaged in a secondary movement task of moving either their

arm or leg. Both movement conditions showed facilitated performance when the same body part

was cued and then moved and impaired performance when a different body part was cued and

then moved. Most interestingly, they subsequently compared participants’ performance on the

body position memory task with an object position memory condition. In this object memory

condition, participants were cued to attend to changes in either the top (white) or the bottom

(yellow) part of a blocked figure. The critical finding of the study was that a facilitated

performance was found for the body position task, but not for the object position condition.

10

These results indicate that the body schema is used to encode body position for both the self and

others. This cognitive representation of body position is separate from representations used to

remember the positions of objects.

In accordance with the earlier behavioral findings, neurophysiological evidence now

confirms that a number of cortical regions may be involved in the processing of bodies.

However, the perception of bodies, like that of faces, evokes a consistent and selective pattern of

neural activity within the extrastriate visual cortex (extrastriate body area- EBA). Using fMRI,

Downing and colleagues (2001) found a region in the lateral occipitotemporal cortex which

yielded a significantly stronger response when subjects viewed images of human bodies and

body parts. This region was less active when viewing animals, and least active during the

perception of inanimate objects such as tools, suggesting a dominance for the processing of

bodies – in particular human bodies (see Peelen & Downing, 2007 for a review). The

neuroimaging evidence for a specialization of the EBA for human body recognition is strongly

supported by complementary evidence that functional interference with neural activity in the

EBA impairs visual processing of human bodies. Temporary inactivation of the EBA with

repetitive transcranial magnetic stimulation (rTMS) selectively impairs discrimination of bodies

but not faces or objects on delayed matching-to-sample visual tasks (Urgesi, Berlucchi &

Aglioti, 2004; Pitcher, Charles, Devlin, Walsh & Duchaine, 2009).

The discovery of the EBA has brought about much clarity in understanding how

individuals perceive the dynamic spatial organization amongst body parts for both the self and

others. However, more research is needed to fully capture an understanding of the body in the

brain. Specifically, questions have been raised as to whether the EBA may respond differentially

to signals from one’s own body and signals from other bodies. Experimental evidence related to

this question is conflicting. Recent fMRI studies by Hodzic and colleagues (2009) show no

differential activation to the presentation of unfamiliar or familiar bodies, including one’s own

body. Other studies have suggested that the EBA is activated more by allocentric than egocentric

views of body parts (Chan, Peelen, & Downing, 2004; Sax, Jamal, & Powell, 2006). Clearly,

although the EBA seems to be preferentially activated during the viewing of human bodies,

aspects of the EBA in the human cortex are still in need of further exploration.

11

1.4.1 Body Schema Development

The body schema is plastic and can be shaped by influences of experience (Berlucchi &

Aglioti, 1997). Specifically, the body schema is thought to develop progressively throughout

childhood and adolescence (Assaiante, Barlaam, Cignetti, & Vaugoyeau, 2014) and improves

through its interactions with the environment and other people. Some developmental studies

have reported that the postural body schema matures later in childhood, from 8 to 10 years old

(Eliasson, Forssberg, Ikuta, Appel, Westling, & Johansson et al. 1995; Schmitz, Martin,

Assaiante, 2002; Assaiante, Mallau, Viel, Jover, & Schmitz, 2005; Cignetti, Chabeauti,

Sveistrup, Vougoyeau, & Assaiante, 2013; see Assaiante et al., 2014 for a review). It appears

that the postural body schema is not fully mature at the age of 8 years of age (Schmitz et al.,

2002). Indeed, a study involving anticipatory postural perturbations involving a bimanual load-

lifting task reported that children as old as 8 years of age had difficulty mastering the

coordination between the arm executing the unloading and the stabilization of the postural

forearm position to allow for an effective grasping of the object (Schmitz et al., 2002). Further,

in a sit-to-stand and back-to-sit task with changes in support surface inclination, children aged 7

to 10 years of age partially adapted their motor strategies in accordance with the tilt surface. The

children’s strategies were not as effective as those of the adults when trying to improve vertical

truck orientation (Cignetti et al., 2013). Thus, despite a partial adaptation, it appears that the

updating of the postural body schema is a process that matures progressively throughout

childhood.

However, it appears that adolescent representations are still far from equaling those of

adults. Specifically, adolescents have been shown to transiently neglect proprioceptive feedback

and over-use visual information to regain postural control as compared to adults when

experiencing slow oscillations (Cignetti, Chabeauti, Vougoyeau, & Assaiante, 2013). Thus, the

body schema continues to mature with development as the body kinetics and brain associations

transition from childhood to adolescence and consolidate in adulthood (Assaiante, et al., 2014).

In particular, changes in cortical development have been associated with the elimination of

unused synapses and a simultaneous myelination of relevant fiber tracts during this period and

stabilizing in early adulthood (Gogtay et al., 2004; Barnea-Goraly et al., 2005). Thus,

fluctuations in cortical development and body kinematics in both childhood and adolescence may

parallel changes occurring in body schema maturation during development.

12

1.4.2 Summary

The identification of body-related cortical areas, such as the EBA, have brought

considerable clarity in linking theoretical conceptual representations of the self and other with

other evidence grounded in the bodily experience. The correspondence between the self and

others may be achieved by identifying the body parts of others and matching those to the

representation of one’s own body parts in the brain. This matching process might allow one to

create a shared neural representation between the self and other. Note, however, that the body

representation of children and adolescents may not be fully developed as both cortical and body

kinematic fluctuations stabilize in adulthood. Although the preceding section reviewed evidence

in favour of general body processing areas, the following section will consist of a review of

behavioural studies that support this self-other body mapping process.

1.5 Body-Part Compatibility

A number of recent studies have assessed the behavioural implications associated with

adult interpersonal body representation. For example, Thomas, Press, and Haggard (2006)

studied adult subjects’ response to a tactile (vibration) stimulus on their own bodies after viewing

a corresponding visual cue on an adult model’s body. Tactile detection was facilitated when the

visual cue was presented on the homologous body part of the observer. Similarly, Bach and

colleagues (2007) found that response times (RT) for finger and foot responses were shorter

when targets were presented over homologous body sites as opposed to another body part of a

model. Specifically, the researchers had participants view static and dynamic images of a model

that had red or blue coloured targets superimposed on the hand, foot, or head. The participants

were instructed to respond with a finger press to a blue target and a foot pedal press to red target

regardless of where it was presented. They found that when there was compatibility between the

target placement on the model’s body and the responding effector of the participant (e.g., blue

target on the hand or red target on the foot), shorter RTs were recorded than when the target was

in another location. That is, finger and foot responses were shorter when the blue or red targets

were presented over the hand and feet, respectively, then when the targets were presented on

another body part of the model. Consistent with Reed and Farah (1995), the authors of these

studies suggested that these body-part compatibility effects emerged because viewing and

attending to homologous body sites of another person can automatically increase the activation

13

and sensitivity of perceptual and motor areas representing that body part in the body schema.

This body-part specific activation subsequently primes and facilitates responses involving the

same body sites of the viewer, and/or perhaps causing interference when the individual needs to

respond with a different limb.

Interestingly, self-other matching can occur between humans and nonhuman mammalian

animals (Pacione & Welsh, in press; Welsh, McDougall, & Paulson, 2014). Following an

adaption of Bach et al. (2007) study, these studies used the body-part compatibility task to assess

the mapping of the fore- and hindlimbs of nonhuman animal bodies on to the homologous limbs

of the human body schema. The results revealed body-part compatibility effects when mammals

(i.e., bears, monkeys, meerkats) were observed in a bipedal posture, but not these same mammals

are in a quadrupedal posture. However, when crossing taxonomical “classes” to include reptilian

and aves images, no limb compatibility effects were observed when the animals (i.e., lizard,

penguin, owl) were in a bipedal posture. Thus, there may be sensitivity in the body schema to the

characteristics (and perhaps class/group) of the body in the observed image.

A fundamental concern that has emerged in the literature is whether these body-part

compatibility effects are modulated by (or are completely due to) pre-existing stimulus-response

spatial compatibility effects (Umilta & Nicoletti, 1990). In typical S-R compatibility tasks,

responses to stimuli are faster if the stimulus is on the spatial orientation (e.g., side of space) as

the responding effector (Simon, 1969). In tasks involving body-part compatibility involving foot

and hand responses, spatial compatibility effects can extend to whole body frames whereby a

hand response is facilitated for “high” target locations and foot responses are facilitated for

targets at “low” spatial locations (Nicoletti & Umilta, 1984, 1985). Thus, because the targets on

the hands and feet of the model are high and low in the display, the spatial and body-part

compatibility effects are confounded.

To address this issue, Wiggett and colleagues (2011) directly investigated whether the

associations learned between executing body actions and observing body actions constitute a

unique kind of association, or whether they were more generalized to spatial codes. Using an

incongruent effector training task, they compared body action priming effects with spatial action

priming effects. Specifically, they presented participants with images of a hand and a foot that

lifted, or two circles that changed in size. The participants were instructed to focus on a letter

14

that was presented in the centre of the screen and ignoring the other stimuli by lifting either their

hand when they saw the letter “H” or their foot when they saw the letter “F”, respectively. The

study had priming conditions in which the letters and the task-irrelevant stimuli were compatible

(e.g., the letter F presented with a foot lift), or incompatible (e.g., a letter F presented with a hand

lift). To be comparable with the body conditions, where a hand is normally positioned above the

foot, the shape conditions were organized such that a hand movement was denoted with a change

in the top circle, while a foot movement was denoted with a change in the bottom circle.

Spatially compatible (e.g., the letter F presented with a change in the bottom circle), or

incompatible (e.g., a letter F presented with a top circle change) conditions were also presented.

Following the priming phase, participants were divided into training groups (i.e., body

compatible, body incompatible, shape compatible, or shape incompatible). In the compatible

groups, the participants’ actions were consistent with the subsequent visual feedback from the

stimuli and in the incompatible groups, participants’ actions were inconsistent with the

subsequent visual feedback from the stimuli. The authors found that action-perception

associations that are related to the body do not appear to generalize to spatial priming effects,

even with specific training. Specifically, the priming effect associated with viewing body parts

was smaller for those who received the incompatible training with body stimuli. In contrast, the

priming effect elicited by spatial compatibility was not modulated by training. That is, there was

no difference between the compatible and the incompatible groups who received training on the

shape stimuli. Additionally, learning effects did not transfer to other domains. For example,

shape incompatible spatial training had no effect on subsequent body compatibility priming

effects. The authors thus concluded that associations between executing and observing body

actions constitute a special kind of learned association.

Additionally, Catmur and Heyes (2011) attempted to determine if spatial and body-part

compatibility effects were independent by assessing the time courses of spatial and body-part

compatibility effects. They had participants complete a choice reaction time task, in which they

responded to coloured targets that were placed either on the index or little finger of a hand

model. Participants were instructed to make an abduction movement of either the index or the

little finger according to the specific colour illuminated. The coloured target was followed by a

task-irrelevant abduction movement of either the index or the little finger movement of the hand

model. The study had testing conditions in which spatial and body frames of reference were

15

aligned and situations where these were in opposite. Using a quintile analysis in which they

binned the RTs in the shortest to longest fifths, the authors were able to assess the magnitudes of

the spatial and body compatibility effects at different points during the course of a trial. The

authors reported that spatial compatibility effects were present in the early stages of a trial and

body compatibility arose later in the trial. These results indicate that spatial and body

compatibility effects display different time courses across a set of trials and, hence, are likely due

to independent mechanisms.

Finally, Wiggett and colleagues (2013) compared spatial and body compatibility effects

across the whole body, using hand and foot responses. They presented task-irrelevant hand and

foot priming stimuli and had participants make hand and foot responses to letters that were

presented in the centre of the screen. Additionally, the authors manipulated the location of the

hand and foot on the screen, placing the hand above the foot on half the trials and reversing the

placement in the other half. Consistent with Catmur and Heyes (2011), the results revealed

different time courses for spatial and body priming effects, with spatial compatible effects

appearing earlier in a trial. Interestingly, the effects of hand/foot location on screen are primarily

found for foot, but not hand responses. Foot responses appear to be more efficient when the body

part location matches the anatomy of the participant compared to when it does not. Taken

together, the results of these studies suggest that both spatial and body compatibility effects exist,

operating simultaneously over separate time courses. The neural systems mediating the spatial

and body compatibility effects are likely different, with body part identity in regions of the EBA

(e.g., Downing et al., 2001; Peelen & Downing, 2007) and egocentric spatial location involving

different cortical regions. The task of resolving response conflict to enable selective action is

likely common to both situations and it is these interactions between the two frames of reference

that will take place in common neural (motor) structures.

1.5.1 Summary

Body-part compatibility tasks appear to be an effective tool to assess self-other matching

and potentially, the involvement of the human body schema in social cognitive processes. Based

on the current data, it has been suggested that seeing another person’s body part leads to an

activation of the representation of that body-part in the body schema of the viewer. This body-

part specific activation subsequently primes and facilitates responses involving the same body

16

sites of the viewer. The correspondence that is achieved between identifying the body parts of

others and matching those to the representation of our own body parts in the brain, allows one to

create a shared neural representation between the self and other. Thus, it is thought that the

processes that lead to the body-part compatibility effect are those that support the human ability

to empathize with, mimic, and understand the actions of other humans. In tasks involving body-

part compatibility, spatial compatibility effects can extend to whole body frames, however,

spatial and body- part compatibility effects appear to operate simultaneously using relatively

independent mechanisms. Overall, the research focus of these studies has centered on the

processes underlying the ability of the adult human to represent the bodies and actions of other

adult humans. Thus, the body-part compatibility task may be well suited to explore the

ambiguities surrounding body representation in children and adolescents.

1.6 Conclusion

Social functions, such as planning one’s own behaviour in a group, anticipating one’s

own and others’ behaviours, and empathizing with others appears to rely on people’s ability to

match the bodies and actions of the others to the representations used to perceive and act the self.

Action-perception mechanisms are thought to facilitate such complex interactions because the

neural codes that are responsible for generating actions are tightly coupled to the codes that

represent the perceptual consequences of those actions (Hommel, 2009; Prinz, 1997). These

representations not only guide one’s own behaviour, but are also used to interpret the behaviour

of others. This action-perception coupling mechanism offers a functional bridge between actions

produced by the self and those produced by others.

Additionally, this ability to understand others is fundamentally enriched by a distributed

neural network that encompasses shared self-other representations (Gallese, 2001). These shared

representations are created when one registers the perceptions and thoughts of others against the

neural representations used to perceive the self. This process asserts that the self and other are

intricately tied together (Lombardo et al., 2010). By means of action simulation, the actions of

another individual could be mapped onto the stored sensory predictions of one’s own actions

(Blakemore & Decety, 2001). Self-other equivalence is particularly relevant for pre-adolescent

and adolescent populations who strive to conform to own-age group norms.

17

This intricate relationship between the self and the other has been recently underlined by

theorists of embodied cognition according to which bodily and action experiences play a primary

role in human cognition - cognitive processes are essentially grounded in bodily states (Gallese

& Sinigaglia, 2011). What makes the behaviour of other agents intelligible is the fact that their

body is experienced as something analogous to one’s own experienced body. This

correspondence is achieved by identifying the body parts of others and matching those to the

representation of one’s own body parts in the brain (Blakemore & Decety, 2001; Jackson &

Decety, 2004; Berlucchi & Aglioti, 2010).

An effective tool to assess self-other matching at the level of the body is the body-part

compatibility task (Bach et al., 2007; Welsh et al., 2014; Pacione et al., in press). Observing a

body or body part is thought to lead to body-part specific activation in the body schema, which

subsequently primes and facilitates responses involving the same body sites of the viewer (Bach

et al., 2007; Reed & Farah, 1995). The correspondence that is achieved between identifying the

body parts of others and matching those to the representation of one’s own body parts in the

brain, allows one to create a shared neural representation between the self and other. Thus, the

body-part compatibility task may be well suited to explore the ambiguities surrounding body

representation in a number of different populations, including children and adolescents.

1.7 The Current Project: Purpose and Specific Hypotheses

The purpose of the present study is to investigate the integrity of mechanisms underlying

the ability to represent the bodies of other humans (i.e., self-other matching) in typically

developing (TD) children and adolescents. To investigate these processes, I will evaluate the

performance of TD individuals using a human body-part compatibility task which provides an

index of the body-part matching process (e.g., Bach et al., 2007; Welsh et al., 2014; Pacione et

al., in press). This information can be used to understand the cognitive underpinnings of how

one’s own body influences one’s perception of others’ body representations.

To this end, participants of different ages will complete a body-part compatibility task in

which targets will be presented over static images of a 7, 11, and 15 year old male model.

Coloured targets will be superimposed over the hand or foot of the models. Participants will be

instructed to execute a left or right key press to red or blue coloured targets, respectively.

18

If the bodies in the images are mapped onto the human body schema of the observer, then

a body-part compatibility effect will be observed and RTs will be shorter when the stimulus is

presented on the compatible body parts (e.g., red stimulus on the hand) than on incompatible

body parts (e.g., red stimulus on the foot) (as in Bach et al., 2007; Welsh et al., 2014; Pacione et

al., in press). If the bodies in the images are not mapped onto the human body schema of the

observer (or if the body schema is not sufficiently developed in the observer), then no body part

compatibility effects will be observed and there will be no differences between RTs to stimuli

presented on the different body parts. With respect to the main research question, it is further

predicted that if children and adolescents of all ages engage in self-other mapping with people of

all ages, then they will be able to map the bodies of all the images onto the human body schema

and body-part compatibility effects will be observed in all cases. Alternatively, if the children

and adolescents resonate most with the bodies of the images that share similar characteristics and

age (i.e., their peer group), then age specific body-part compatibility effects will be observed. In

this latter scenario, body-part compatibility effects will only be observed with the 7 year old

model type for children in the 7 to 9 year old age group. For children in the 10 to 12 year old age

group, body-part compatibility effects will only be observed with the 11 year old model type.

Finally, body-part compatibility effects will only be observed with the 15 year old model type for

adolescents in the 13 to 16 year old group.

19

Chapter 2 Research Article

2.1 Introduction

In daily life, humans are constantly interacting with other people - be it helping a child

grab a glass off a high shelf or talking with neighbours. Adults are able to identify with the

bodies and actions of others in order to engage in a shared experience of the world. This is

particularly true when an adult is asked to pass a jug of water to a child. The adult must consider

if the child can manage the weight of the object, thus identifying with the child’s body. One of

the processes that is thought to facilitate this complex ability of understanding others is one in

which humans register the perceptions and thoughts of others against the neural representations

used to perceive the self. Evidence for self-other mapping comes from different sets of studies

revealing a facilitatory effect in responses to observing body parts in static (e.g., Bach, Peatfield,

& Tipper, 2007; Thomas, Press, & Haggard, 2006) and dynamic (e.g., Brass, Bekkering, &

Prinz, 2001; Catmur, & Heyes, 2011; Wiggett, Downing, & Tipper, 2013; Wiggett, Hudson,

Tipper, & Downing, 2011) displays. For example, Bach et al. (2007) studied the response times

of adults to coloured targets that were superimposed over an adult model’s body. They found that

response times (RT) for finger and foot responses were shorter when targets were presented over

the hand and feet, respectively, of an adult model than when the targets were presented over

another body part of the model (see also Jovanov et al., 2015; Thomas et al., 2006). The authors

suggested that these body-part compatibility effects emerged because viewing and attending to a

target on homologous body sites can automatically increase the activation and sensitivity of

perceptual and motor areas representing that body part in the observer’s body schema. This

body-part specific activation subsequently primes and facilitates responses involving the same

body sites of the viewer, or interferes with responding when the response involves a different

limb.

Overall, the findings of studies exploring this body-part compatibility effect are

consistent with research that has centered on the cognitive and neural processes underlying the

ability of the adult human to represent the bodies and actions of other adult humans (e.g., Ogden,

1985; Peelen & Downing, 2007; Reed & Farah, 1995; Sirigu, Grafman, Bressler, & Sunderland,

1991). Evidence for this ability to code body parts was initially derived from neuropsychological

20

studies that revealed that humans possess a body schema or a mental construct devoted to the

dynamic spatial organization amongst parts of the body of the self and its relations to that of

other bodies (Semenza & Goodglass, 1985; Semenza, 1988; Ogden, 1985; Sirigu, Grafman,

Bressler, & Sunderland, 1991). It is thought that a body representation (or schema) is used for

the unconscious encoding of body position for both the self and others and this cognitive

representation is separate from representations used to remember the positions of objects (Reed

& Farah, 1994). In accordance with the earlier behavioral findings, neurophysiological studies

suggest that a consistent and selective pattern of neural activity within the extrastriate visual

cortex (extrastriate body area [EBA]) is evoked during the perception of bodies (Downing et al.,

2001). The EBA exhibited a significantly stronger response when subjects viewed images of

human bodies and body parts. It became less active when viewing animals, and least active

during the perception of inanimate objects such as tools, suggesting a dominance for the

processing of bodies – in particular human bodies (see Peelen & Downing, 2007 for a review).

Thus, this research indicates that the body schema can encode body parts of both the self and

other. It is thought that this body schema is what supports self-other matching, at least with

respect to body parts.

It is important to note here that the research reported above has focused on these

processes in adults. The processes leading to the child and adolescent’s ability to understand the

bodies of other children and adolescents has, to our knowledge, received no direct experimental

attention. The present study was conducted to provide some initial insights into the complex

child-to-child social cognitive process of body-part matching.

Although no research, to our knowledge, has explored body schema use in self-other

matching in this manner, there has been some research related to the development of the body

schema for understanding the self. Investigations of the developing body schema of the self in

childhood and adolescence have centered on transiently disturbing sensory information, in

particular proprioceptive and visual messages, during sit-to-stand, tendon vibration, and illusory

motion tasks (Eliasson, Forssberg, Ikuta, Appel, Westling, & Johansson et al. 1995; Schmitz,

Martin, Assaiante, 2002; Assaiante, Mallau, Viel, Jover, & Schmitz, 2005; Cignetti, Chabeauti,

Sveistrup, Vougoyeau, & Assaiante, 2013; see Assaiante et al., 2014 for a review). These studies

have highlighted the plasticity of the developing postural body schema, focusing specifically on

how the individual perceives the self through transient postural disturbances. Overall, these

21

studies have centered on examining the development of the postural body schema from an

intrapersonal frame of reference. Specifically, the body schema is thought to develop

progressively throughout childhood and adolescence, with some developmental studies reporting

that the body schema matures later, from 8 to 10 years old (Eliasson, Forssberg, Ikuta, Appel,

Westling, & Johansson et al. 1995; Cignetti, Chabeauti, Sveistrup, Vougoyeau, & Assaiante,

2013). Thus, as the body kinetics and brain associations transition from childhood to

adolescence and consolidate in adulthood, the body schema is thought to continue to mature with

development (Assaiante, et al., 2014). However, despite a body of work on the individual

development of the postural body schema, little work has examined the interpersonal interactions

between children, specifically, the development of associations created between children’s own

bodies and the bodies of other children.

Although the emergence of body-part compatibility effects occurring during adult-to-

adult interactions suggests that self-other body-part matching occurs in adults, researchers have

yet to examine these effects in child and adolescent populations. This gap in the literature has

emerged despite the fact that childhood and adolescence would seem to be a time of particular

relevance for studying the development of intra- and inter-body representations. The transition

from middle childhood to late childhood and adolescence involves a great deal of peer

socialization. Children may have a preference for members of their own age groups who share

similar behaviours, interests, and activities (Abrams, Rutland, Cameron, & Marques, 2003).

Older children and adolescents are more self-conscious of their self-presentation and may strive

for consistency with their own age peers in order to conform to in-group norms and avoid own-

age group segregation (Abrams, Rutland, Cameron, & Ferrell, 2007; Martin, Fabes, & Hanish,

2014). Similarly, indirect investigations exploring the effect of viewing peer versus adult model

stimuli have yielded parallel results. Specifically, Marshall and colleagues (2010) found stronger

motor contingent effects when children observed dynamic images of their own peer than an adult

model (see also Liuzza, Setti, & Borghi, 2012).

The purpose of the present study is to investigate the integrity of mechanisms underlying

the ability to represent the bodies of other humans (i.e., self-other matching) in typically

developing (TD) children and adolescents. To this end, participants will complete a body-part

compatibility task while viewing static images of a 7, 11, and 15 year old male model.

Participants will execute left or right key presses to red or blue targets, respectively, which will

22

be presented on the hand or foot of the model. If the bodies in the images are mapped onto the

human body schema of the observer, then a body-part compatibility effect will be observed and

RTs will be shorter when the stimulus is presented on the compatible body parts (e.g., red

stimulus on the hand) than on incompatible body parts (e.g., red stimulus on the foot) (as in Bach

et al., 2007; Welsh et al., 2014; Pacione &Welsh, in press). If the bodies in the images are not

mapped onto the human body schema of the observer, then no body part compatibility effects

will be observed and there will be no differences between RTs to stimuli presented on the

different body parts. Additionally, it is further predicted that if the individuals are able to map the

body-parts of all the images onto their own body schema, then body-part compatibility effects

will be observed in all cases. Alternatively, if the individuals resonate most with the bodies of the

images that share similar characteristics and age (i.e. their peer group), then age specific body-

part compatibility effects will be observed.

2.2 Methods

2.2.1 Participants

Forty-one typically developing children (32 males, 9 females; mean age = 11.3 years old;

range = 7-16; SD = 2.86) volunteered to take part in the study with their parents/guardians

providing informed consent prior to beginning data collection. For their participation, all children

were financially compensated ($10). An additional two children were recruited, but their data

were excluded due to an inability to complete the task. All participants completed abbreviated

versions of the Edinburgh handedness inventory to assess hand dominance and the Ishihara

colour plates 38 set to ensure that none of the children were colour blind. Two of the children

were left-hand dominant, two were ambidextrous, and the remaining 37 were right-hand

dominant. All participants were naïve to the purpose of the study.

The protocol was completed in a single session that lasted 30-45 minutes. The procedures

were consistent with the codes of the Declaration of Helsinki and were approved by the

University of Toronto Research Ethics Board.

2.2.2 Apparatus, Task, and Procedure

A group of participants (n= 31) performed the task in a laboratory where they sat in a

chair at a desk approximately 70 cm away from a computer screen. All stimuli were presented

23

on a 16” LCD screen. A second group of participants (n= 10) performed the task at home, where

the experimenter projected the program from a laptop to a 16” LCD computer monitor. The same

experimenter oversaw the testing in both sites. Stimuli consisted of real-life profile colour

pictures of three male models - a ~7 year old child, a ~11 year old child, and a ~15 year old

adolescent in a standing posture (see Figure 2.1). The models all wore similar clothes (jeans and

a plain black t-shirt). These 3 images were flipped horizontally such that each of the images was

presented in a rightward and leftward profile orientation (i.e., a total of 6 images were used). The

images of each model were carefully selected amongst a series to match the other images on

perspective, hand and feet position, and head and eye orientation as closely as possible. The

images presented displayed all limbs and the whole face from a frontal view, with the face and

eye gaze directed at the participant.

Each body was digitally extracted from the original environment and positioned on a

neutral white background. The figures were separated from their environment to prevent

irrelevant information in the background from distracting the participants and to highlight the

target stimuli. Each image varied in height to reflect the differences in age. The 7 year old model

was the shortest (17 cm [h] x 7 cm [w]), followed by the 11 year old model (18.5 cm [h] x 8 cm

[w]) and the 15 year old model was the tallest (20.5 cm [h] x 9.5 cm [w]).

A single target was presented on each picture. The target was a blue or red circle (1 cm

diameter) that was superimposed over one of the most distal structures (hand or foot) of the

models. Blue and red circles were presented equally often on the different limbs. Because the

relative proportions of the different bodies differed slightly, the specific location of each target

for each model condition differed slightly. For the 7 year old model, targets appearing on the

hand were 11 cm from the bottom of the screen. Targets appearing on the foot appeared 4.5 cm

from the bottom of the screen. For the 11 year old model, the targets appearing on the hand

appeared 10.5 cm from the bottom of the screen and the targets appearing on the foot appeared

3.5 cm from the bottom of the screen. For the 15 year old model, the targets appearing on the

hand appeared 11.5 cm from the bottom of the screen and the targets appearing on the foot

appeared 3 cm from the bottom of the screen. The images were also equally presented in a

rightward or leftward profile orientation, such that the targets appeared equally as often on the

right and left limbs.

24

Figure 2.1. Examples of the 7, 11, and 15 year old models with coloured targets. Only a single

image was presented on each trial. The black boxes surrounding each image were not presented

in the experiment, but were included here to demonstrate the different sizes and proportions of

the images.

Further, two images were created by digitally removing the model body from the

coloured targets (see Figure 2.2). An upper and lower coloured target image was presented,

which roughly represented the locations of the hand and foot target positions on the model

bodies, respectively. Targets appearing in the upper space were 11 cm from the bottom of the

screen. Targets appearing in the lower space appeared 3.5 cm from the bottom of the screen.

These two images were flipped horizontally such that each of the images was presented in a

rightward and leftward spatial orientation (i.e., a total of 4 images were used). Blue and red

circles were presented equally often at the upper and lower spatial locations.

25

Figure 2.2. Examples of the coloured targets in lower and upper space. The black boxes

surrounding each image were not presented in the experiment, but were included here to

demonstrate the different locations of the targets in the trials.

The task consisted of a two-choice hand response task. Participants placed their left

index finger over the “z” key and their right index finger over the “3” key on the number pad of a

standard English language keyboard. Participants were told to press the “z” and “3” keys with

their index fingers as soon as possible when a red or blue circle, respectively, was recognized in

the picture. Instruction screens that outlined the task were presented prior to each block in a

black font on a white background. A custom program written using E-Prime (2.0) software

controlled the presentation of the experimental stimuli and recorded the timing and identification

of the responses.

There were two main tasks in the study – a spatial compatibility and a body-part

compatibility task. The spatial compatibility task was conducted to ensure that the participant

could follow instructions and complete the basic task. The data from this task were also

analyzed to test for any pre-existing upper or lower spatial compatibility effects. The spatial

compatibility task consisted of a block of 24 trials of the choice response task with the images of

the upper and lower coloured targets. There were no bodies in the spatial images (see Figure

2.2). The 24 trials in this spatial compatibility block consisted of three instances of each image

(the factorial combination of target [red, blue], spatial field [upper, lower], and orientation [left

or right]) presented in random order.

26

Following the spatial compatibility task, a familiarization session of six randomized trials

with images that included the models was presented before completing the body-part

compatibility task. The body-part task consisted of five blocks of 24 trials of the choice response

task with the model images. The 24 trials in each block consisted of a single instance of each

image (the factorial combination of target [red, blue], model [7 year old, 11 year old, 15 year

old], limb [hand, foot], and orientation [facing left or right]) presented in a random order within

each block.

At the beginning of each trial, the word “READY” was presented 8 cm from the bottom

of the white screen with black font; a location that was roughly equidistant between the potential

location of a hand or foot target. The experimenter advanced the “READY” cue for each trial

when she was confident the participant was focused on the task and ready to complete a trial.

Following the “READY”, a black fixation cross was positioned at the same location to direct and

maintain attention to the lower portion of the screen during the foreperiod. Target images were

presented randomly 1000-3000 ms after the presentation of the fixation cross to discourage

anticipation. The picture was positioned such that the targets were equidistant from the

“READY” and fixation cross and the feet of the models were 3-4 cm from the bottom of the

screen.

2.3 Results

The children were divided into three groups for analysis (7 to 9: n = 13; 10 to 12: n = 14;

13 to 16: n = 14). Two main sets of analyses, one on the spatial compatibility and one on the

main body-part compatibility data, were conducted to address specific theoretically-relevant

questions.

2.3.1 Spatial Compatibility

RT data for the spatial compatibility trials on which the participant executed the wrong

response (e.g., a right hand response, instead of a left hand response, for a red target) were

eliminated (4.6% of all trials) (see Table 2.1). After the wrong response trials were removed,

RTs were collapsed across side of space within the upper and lower spatial trial types to create a

mean RT value for upper and lower fixation for each participant. Mean RTs for the spatial

compatibility task were submitted to a 3 (Group: 7 to 9, 10 to 12, 13 to 16) by 2 (Spatial Height:

27

Upper, Lower) mixed ANOVA with repeated measures on the last factor. Alpha was set at 0.05

for all tests. All significant effects are reported.

No significant main effect of Spatial Height was found, F (1, 38) = 0.578, MSE =

2,640.53, p = 0.452, ηp2 = 0.015. A significant effect of Group was found, F(2, 38) = 18.26, MSE

= 25,342.12, p<0.001, ηp2 = 0.49. Planned comparisons were conducted by collapsing the RTs of

all the trial types for each participant. The analysis revealed that the mean RTs for the 13 to 16

year old group (M = 483 ms, SD = 79) were significantly shorter than that of both the 10 to 12

year old group (M = 637 ms, SD = 121), t(26) = 3.99, p<0.001, and the 7 to 9 year old group (M

= 743 ms, SD = 133), t(25) = 6.24, p<0.001. The mean RTs for the 10 to 12 year old group were

also significantly shorter than the 7 to 9 year old group, t(25) = 2.17, p = 0.04.

Of greater theoretical relevance, there was no significant Group by Spatial Height

interaction, F(2, 38) = 0.628, MSE = 2,640.53, p = 0.539, ηp2 = 0.032. Overall, the results reveal

no pre-existing upper or lower spatial field effects amongst the upper and lower coloured stimuli.

Thus, any body-part compatibility effects that may emerge with the body-part compatibility task

are not likely to be modulated by pre-existing upper or lower spatial effects.

Table 2.1. Mean (and standard deviations) of the % of response errors as a function of

Presentation Side, Responding Effector, and Spatial Height.

Presentation Side

Spatial

Height

Effector Upper Lower

Left Side

Left Hand 2.44 (8.79) 3.25 (10.01)

Right Hand 5.69 (12.70) 9.76 (15.35)

Right Side

Left Hand 4.06 (11.04) 6.50 (13.37)

Right Hand 1.62 (7.26) 3.25 (10.01)

28

2.3.2 Body-Part Compatibility

RT data for the test trials on which the participant executed the wrong response were

eliminated (3.1% of all trials). After the RTs for the wrong response trials were removed, the

data were collapsed across right/leftward orientation and a mean and standard deviation for each

participant, for each limb condition (hand, foot) were derived. Trials where no response was

recorded and those that were greater than 3 standard deviations above the mean for a condition

for each individual were considered outliers and were deleted (1% of all trials). Overall, 4.1% of

all trials were deleted as anticipation error (defined as RTs shorter than 100 ms), inattention

errors, wrong responses, no responses, or outliers. Table 2.2 displays the execution errors

(incorrect responses) across each limb condition.

Table 2.2 Mean (and standard deviations) of the % of response errors as a function of

Presentation Side, Responding Effector, Model Type, Target Location.

Mean RTs for the test stimuli were submitted to a 3 (Group: 7 to 9, 10 to 12, 13 to 16) by

3 (Model: 15 year old, 11 year old, 7 year old) by 2 (Target Location: Hand, Foot) mixed

ANOVA with repeated measures for the last two factors. Planned comparisons were conducted

during the post-hoc analyses. Alpha was set at 0.05 for all tests. All significant effects are

reported.

Presentation

Side

Model Type

7 Year Old 11 Year Old

15 Year Old

Effector Hand Foot Hand

Foot

Hand

Foot

Left Side

Left Hand

0.49

(3.12)

0.49

(3.12)

0.49

(3.12)

1.46

(6.91)

2.44

(6.62)

1.46

(5.27)

Right Hand

3.90

(9.19)

3.90

(9.19)

6.34

(11.34)

5.36

(8.98)

4.89

(11.64)

5.85

(9.21)

Right Side

Left Hand

3.90

(8.02)

4.89

(9.78)

6.34

(11.34)

4.39

(8.38)

4.39

(10.5)

4.39

(8.38)

Right Hand

0.49

(3.12)

1.46

(5.27)

2.44

(6.62)

2.93

(8.44)

0.97

(4.36)

0.49

(3.12)

29

The analysis of RTs revealed a trending main effect of Target Location, F (1, 38) = 3.27,

MSE = 1,753.24, p = 0.07, ηp2 = 0.079. Overall, RTs were shorter to targets presented on the

hand (M = 686 ms, SD = 171) than for targets on the foot (M = 695 ms, SD = 179). A significant

effect of Group was also found, F(2, 38) = 23.42, MSE =84,796.62, p<0.001, ηp2 = 0.552.

Planned comparisons were conducted by collapsing the RTs of all the trial types for each

participant. Table 2.3 and 2.4 outline the associated group descriptive statistics and the planned

comparisons across the three groups.

Group 7 yr. Model

Hand Foot

11 yr. Model

Hand Foot

15 yr. Model

Hand Foot

Group

Mean

7 to 9 847 (95)

838 (118)

815 (99)

846 (138)

830 (116)

855 (134)

839 (108)

10 to 12 713 (144)

702 (139)

706 (144)

740 (148)

716 (159)

712 (152)

715 (144)

13 to 16 525 (100)

523 (96)

535 (110)

530 (107)

514 (85)

543 (112)

528 (99)

Condition

Means

691 (175)

684 (174)

682 (165)

702 (185)

683 (179)

700 (183)

Table 2.3. Mean (and standard deviation) response times in milliseconds for each of the three

Groups as a function of Model Type and Target Location. Marginal means are also provided.

Pair t df Sign. (2-tailed)

7 to 9 vs. 10 to 12 2.51 25 .019*

10 to 12 vs. 13 to 16 3.99 26 <.001*

7 to 9 vs. 13 to 16 7.77 25 <.001*

Asterisks indicate significant difference between groups, p <.05 *.

Table 2.4. Planned comparison of response time differences across the three age groups.

30

Of greater theoretical relevance, there was a significant Model by Target interaction, F(2,

76) = 3.35, MSE = 1,376.21, p = 0.04, ηp2 = 0.081. Planned comparisons for the 2-way

interaction revealed no significant body-part compatibility effects when viewing the 7 year old

model type, t(40) = 0.88, p = 0.380. Significant body-part compatibility effects were found when

viewing both the 11 year old, t(40) = 2.07, p = 0.04, and 15 year old, t(40) = 2.10, p = 0.04,

model types.

Although the 3-way Group by Model by Target interaction was not significant, F(4, 76) =

1.88, MSE = 1,376.21, p = 0.12, ηp2 = 0.90, separate ANOVAs were conducted for each age

group to determine if any age-specific body-part compatibility effects emerged when viewing the

various model types (i.e., consistent with a priori prediction). The mean RT values for each

group were submitted to a 3 (Model: 15 year old, 11 year old, 7 year old) by 2 (Target Location:

Hand, Foot) repeated measures ANOVA. The results of this analysis are reported in the

following sections.

Note that the patterns of execution errors were generally consistent with the pattern of

RTs (lower errors or higher accuracy in conditions with shorter RTs) suggesting that the patterns

of RTs were not due to a speed-accuracy trade-off. Due to concerns over there being an

insufficient number of errors across the participants and the conditions to conduct a meaningful

and reliable analysis on the number of errors, an ANOVA on errors was not conducted.

2.3.2.1 7 to 9 year old Group

The ANOVA revealed that the Model by Target interaction that was significant in the

main analysis, was not significant in this age-group analysis, F(2, 24) = 1.41, MSE = 2,122.75, p

= 0.26, ηp2 = 0.105. Further, planned comparisons were conducted by averaging the RTs of all

the hand and foot trial types separately, per model type for each participant. The analysis

revealed no significant body-part compatibility effects occurring when viewing any of the three

model types- 7 year old model t(12) = 0.47, p = 0.64, d = 0.14, 11 year old model t(12) = 1.32, p

= 0.21, d = 0.41, 15 year old model t(12) = 1.64, p = 0.12, d = 0.48 (Figure 2.3). This pattern of

findings suggests that the activation or mapping of body-parts to the human body schema may be

underdeveloped. Thus, the absence of differences in RTs across the different model types

suggests that the body schema and other mechanisms associated with body representation may

not be fully developed at this stage of childhood.

31

Figure 2.3. Mean response time in milliseconds for the 7 to 9 year old group as a function of

model type and target location. Standard error of the mean bars are depicted. Note that the

response time scale is consistent across Figures 2.3, 2.4, 2.5 at 200 ms, although the ranges over

which the data are depicted are different.

2.3.2.2 10 to 12 year old Group

The ANOVA revealed a significant Model by Target interaction, F(2, 26) = 3.56, MSE =

1,168.12, p = 0.04, ηp2 = 0.215. Planned comparisons were conducted by averaging the RTs of

all the hand and foot trial types separately, per model type for each participant. Specifically, a

significant body-part compatibility effect occurred when viewing the 11 year old model type,

t(13) = 2.47, p = 0.03, d = 0.66 (Figure 2.4). No significant effects were found for either the 7

year old model type, t(13) = 0.72, p = 0.48, d = 0.19 or the 15 year old model type, t(13) = 0.26,

p = 0.80, d = 0.07. This pattern of findings suggests that the activation or mapping of body-parts

to the human body schema may be age-specific, with a facilitated response when responding to

images of one’s own peer, at least during this developmental stage.

32

Figure 2.4. Mean response time in milliseconds for the 10 to 12 year old group as a function of

model type and target location. Standard error of the mean bars are depicted. Asterisks indicate

significant difference between target locations, p <.05 *.

13 to 16 year old Group

The ANOVA for the oldest group revealed a trending, but non-significant, Model by

Target interaction, F(2, 26) = 2.83, MSE = 895.17, p = 0.07, ηp2 = 0.179. Planned comparisons

were conducted by averaging the RTs of all the hand and foot trial types separately, per model

type for each participant. Specifically, a significant body-part compatibility effect occurred only

when viewing the 15 year old model type, t(13) = 2.38, p = 0.03, d = 0.78 (Figure 2.5). No

significant effects were found for either the 7 year old model type, t(13) = 0.24, p = 0.82, d =

0.06 or the 11 year old model type, t(13) = 0.65, p = 0.53, d = 0.17. Overall, these results are

consistent with an age specific body-part hypothesis, with a facilitated response when responding

to images of one’s own peer.

33

Figure 2.5. Mean response time in milliseconds for the 13 to 16 year old group as a function of

model type and target location. Standard error of the mean bars are depicted. Asterisks indicate

significant difference between target locations, p <.05 *.

2.3.3 Correlation of Upper and Lower Spatial RTs with Body-Part RTs

Overall, the data from the test phase suggest that a body-part compatibility effect emerges

for the 10-12 and 13-16 year old groups when they are observing their peers. Although the initial

analysis of upper and lower target locations in the spatial compatibility task (reported in section

2.3.1) indicated that there was no difference between targets in these locations when the image of

the model was not present, it is still possible that spatial coding mechanisms contributed to the

patterns of body-part compatibility effects. To further analyze the effect of upper and lower

spatial compatibility on body-part compatibility, difference scores were calculated between mean

RTs for body-part (hand/foot) stimuli and mean RTs for spatial (upper/lower) height. These

difference scores were then submitted to a Pearson correlation analysis to determine if there was

a relationship between the magnitudes of the difference scores across individuals. The logic

behind this test was that if a spatial coding mechanism (and not body-part matching) was

responsible for the patterns of RTs observed in the main body-part analysis, then the magnitudes

of each individuals’ difference scores should be similar across the spatial and body-part stimuli.

It was found that the difference scores for body-part stimuli are not significantly correlated with

the difference scores of the spatial RTs for all three groups - 7 to 9 year old: r = 0.09, p = 0.77

(Figure 2.6); 10 to 12 year old group: r = -0.34, p = 0.23 (Figure 2.7); 13 to 16 year old: r = 0.10,

34

p = 0.71 (Figure 2.8). These results suggest that the body-part compatibility effects that emerged

with the body-part stimuli are likely not related to any pre-existing spatial capability effects.

Figure 2.6. Correlation of body-part difference scores from the body-part compatibility task (y-

axis) as a function of the spatial difference scores from the spatial compatibility task (x-axis) for

the 7 to 9 year old group.

Figure 2.7. Correlation of body-part difference scores from the body-part compatibility task (y-

axis) as a function of the spatial difference scores from the spatial compatibility task (x-axis) for

the 10 to 12 year old group.

35

Figure 2.8. Correlation of body-part difference scores from the body-part compatibility task (y-

axis) as a function of the spatial difference scores from the spatial compatibility task (x-axis) for

the 13 to 16 year old group.

2.4 Discussion

The purpose of the present study was to investigate the integrity of mechanisms

underlying the ability to represent the bodies of other humans (i.e., self-other matching) in

typically developing (TD) children and adolescents. Specifically, the current study sought to

examine the interpersonal interactions between children and adolescents. The findings revealed

that the limbs of children and adolescents are mapped onto the homologous representation in the

human body schema of the observing child and adolescent, but only for specific age groups and

certain stimuli. Specifically, body-part compatibility effects were found for both the 10 to 12 and

13 to 16 year old age groups. On the other hand, an absence of body-part compatibility effects

was found for the 7 to 9 year old age group when viewing any of the three model types.

Additionally, the body-part compatibility effects that emerged were not modulated by pre-

existing upper and lower spatial compatibility effects. Most interestingly, the body-part

compatibility effects that emerged for both the 10 to 12 and 13 to 16 year old age groups

occurred only when viewing models of their own peers. In sum, the results are consistent with an

age specific body-part hypothesis in that older children and young adolescents only engaged in

self-other body-part mapping with the image of an age-related peer. Finally, the absence of

differences in RTs across the different model types for the 7 to 9 year old age group suggests that

the body schema and/or other mechanisms associated with body representation and body

36

mapping may not be fully developed at this point in childhood. The following discussion will

review these results in the context of an age specificity associated with the body schema.

The results and conclusions of an age specificity associated with the body schema are

broadly consistent with the own-age bias observed in facial processing in early childhood. For

example, Anastasi and Rhodes (2005) reported that children aged 5 to 8 years old had higher

levels of facial recognition scores when viewing other child versus adult faces. These results

were confirmed by Melinder and colleagues (2010) who also found an increased amplitude of the

N170 component of the visual event related potential when children viewed child versus adult

faces (see also Hills & Lewis, 2011). Thus, the present data indicate that the own-age bias seen

in facial processing may also extend to the body schema when mapping homologous body parts

of one’s peer.

Additionally, age specific effects have been found in studies that have indirectly

compared the influence of peer versus adult models. When investigating motor resonance in

children, Liuzza and colleagues (2012) found that children responded faster when a hand prime

was of a child’s as opposed to an adult’s. In another study, Marshall and colleagues (2010)

investigated motor contagion in children. They found that the presence of background

movements made by the same-age model was associated with an increase in motor contagion

relative to the condition in which an adult was the background model. These findings lend

support for a same-age bias in body mapping with children and adolescents. Specifically, body

mapping may be facilitated when there is greater age congruency between the observers own

body and that of the observed.

Perceptions of similarity and congruency are particularly relevant for adolescents and

children in late childhood. Adolescence and pre-adolescence are time periods of great peer

socialization which has a great deal of theoretical importance for understanding the development

of intra- and inter-body representations. Specifically, the organization of schools and community

settings create own-age group segregation with children and adolescents spending large amounts

of time with same age peers (Martin, Fabes, & Hanish, 2014). Further, children and adolescents

begin to develop a preference for members of their own age groups who share similar interests,

behaviours, and activities. Finally, children and adolescents begin to strive for consistency

between the self and other as social pressure to act in accordance with one’s group and to

37

conform to the social norms of the in-group takes more of a precedence in later childhood and

adolescence (Abrams, Rutland, Cameron, & Ferrell, 2007). Thus, a heightened awareness of

one’s own body in relation to a same aged peer’s body (as observed in the present study) may be

a manifestation of these contexts and experiences. This particular importance in maintaining peer

group norms for adolescents and pre-adolescents may be due to fears of own-age group

exclusion and peer rejection (Abrams, Rutland, Cameron, & Marques, 2003).

In regards to the lack of compatibility effects found in the 7 to 9 year old age group, this

result may be due in part to an underdevelopment associated with the body schema and other

mechanisms associated with body representation. In particular, the body schema is thought to

develop progressively throughout childhood and adolescence, with some developmental studies

reporting that the body schema matures later, from 8 to 10 years old (Eliasson et al., 1995;

Cignetti et al., 2013). Thus, the large amount of variability seen in this group may reflect the

differences in the rate of progression of body representation development across different

children. Alternatively, the absence of age specific compatibility effects seen with the 7 to 9 year

old model may originate from the physically smaller size of the model’s body. Specifically, the

distance between the targets placed on the hands and feet of the model may have not been

enough spatial distance between the two targets and subsequently participants did not view them

as separate entities. Thus, it is possible that with more spatial distance between the targets, body-

part compatibility effects may have emerged. Finally, it is also possible that compatibility

effects did not emerge because the participants failed to fully understand the task, or because

they took sufficient time to resolve any particular conflicts or interference effects prior to

responding. The fact that this group had the longest RTs of all groups is consistent with either of

these possibilities. Future research may well distinguish between these alternatives.

In sum, the findings of the present study support the notion that the limbs of children and

adolescents can be mapped onto the homologous body-part representations in the human body

schema of the observing child and adolescent. Specifically, body-part compatibility effects were

found for both the 10 to 12 and 13 to 16 year old age groups. On the other hand, an absence of

body-part compatibility effects was found for the 7 to 9 year old age group when viewing any of

the three model types. It is suggested that the absence of differences in RTs across the different

model types for the 7 to 9 year old age group may be due in part to an underdevelopment

associated with the body schema and other mechanisms associated with the body representation.

38

Most interestingly, the body-part compatibility effects that emerged for both the 10 to 12 and 13

to 16 year old age groups occurred when viewing models of their own peers. In sum, the results

are consistent with an age specific body-part hypothesis, with a facilitated response when

responding to images of one’s own peer. Future work could address whether adults are more

sensitive to mapping the body-parts of other adults than of those belonging to children or

adolescents.

39

Chapter 3 General Discussion

3.1 Findings and Implications

The purpose of the present research was to investigate the integrity of mechanisms

underlying the ability to represent the bodies of other humans (i.e., self-other matching) in

typically developing (TD) children and adolescents. Specifically, it was investigated if children

and adolescents map the body parts of other children and adolescents onto their own body

schema and how the observer’s and model’s age might influence this mapping. The results

revealed that the limbs of children and adolescents are mapped onto the homologous

representation in the human body schema of the observing child and adolescent but only under

certain conditions. Specifically, body-part compatibility effects were found for both the 10 to 12

and 13 to 16 year old age groups. On the other hand, no body-part compatibility effects were

found for the 7 to 9 year old age group when viewing any of the three model types. Most

interestingly, the body-part compatibility effects that emerged for both the 10 to 12 and 13 to 16

year old age groups occurred only when viewing models of their own peers.

In sum, the results are consistent with an age-specific body-part hypothesis, with a

facilitated response when responding to images of one’s own peer. These results are broadly

consistent with the own-age bias observed in facial processing in early childhood. Specifically,

higher levels of facial recognition scores were reported when children viewed other children’s

faces (Anastasi & Rhodes, 2005; Melinder et al., 2010; Hills & Lewis, 2011). Similarly, indirect

investigations exploring the effect of viewing peer versus adult model stimuli have yielded

parallel results. In particular, separate studies on motor resonance and motor contagion reported

stronger effects when children observed dynamic images of their own peer (Marshall et al., 2010;

Liuzza et al., 2012). Taken together, the current results of the present study lend support for the

idea that body mapping, like that of facial recognition, may be facilitated when there is greater

age congruency between the observers own body and that of the observed. It is possible that

these age-specific effects arise because peer interactions at schools and community settings are

formally structured to facilitate same age interactions. Thus, the age-specific effect might have

further arisen because people of these age groups are more often exposed to and see people of a

similar age than of other age-groups. This exposure to similar aged individuals might prime or

40

otherwise enhance the efficiency with which these bodies and faces are processed relative to

others. In the end, this facilitated identification with one’s peer may be a reflection of shared

neural representations between the self and other, where the body of one’s peer is experienced as

something analogous to one’s own experienced body. Thus, this correspondence is achieved by

identifying the body parts of others and matching those to the representation of our own body

parts in the brain (Blakemore & Decety, 2001; Jackson & Decety, 2004; Berlucchi & Aglioti,

2010).

Additionally, the reason the age-specific effect only emerged for the 10 to 12 and 13 to

16 year old groups is because greater identification with one’s peer is of particular importance

for adolescents and pre-adolescents who strive for similarity and congruency with in-group

norms (Abrams, Rutland, Cameron, & Ferrell, 2007). Specifically, adolescents and pre-

adolescents will strive for consistency with their own age groups to avoid peer segregation and

exclusion. Thus, these older children may be more sensitive and self-conscious of their public

self-presentation (Martin et al., 2014). Our results are in line with such conclusions, in particular,

age-specific body-part compatibility effects were found with the oldest age groups (10 to 12

years of age and 13 to 16 years of age), which represent pre-adolescent and adolescent children,

respectively. Thus, when viewing images of their own peers, pre-adolescents and adolescents

may be more aware of the bodies of their peers than younger individuals resulting in facilitated

RTs or greater interference when the response involves a different limb for these age groups.

Overall, our results suggest that body-part mapping may be own-age specific, particularly with

pre-adolescents and adolescents. Thus, the transition from middle childhood to late childhood

and adolescence can be a pivotal time in the development of intra- and inter-body

representations.

Finally, it should be noted here that it is not suggested that the absence of differences in

RTs across the different model types for the 7 to 9 year old age group indicates that the body

schema is dysfunctional or not intact in this age group. The point raised here is that is it possible

that the intricate processes of self-other mapping may not be fully developed in this age group. It

is clear that humans are equipped with a rudimentary knowledge about the dynamic organization

not only of one’s own body, but also of its relations to other bodies at a very early age. Even

minutes after birth, infants show a strong innate tendency to mimic sounds and oro-facial motor

acts performed by the adult models in front of them (Meltzoff & Moore, 1977). This data

41

indicates that the substrates of a self-other matching system are functioning early in infancy. The

absence of a body-part compatibility effect for the 7 to 9 year olds in the present study, however,

may indicate that children in early to middle childhood may not be as self-conscious of their own

and peers bodies because the desire to maintain peer group norms is less salient as those

experienced by pre-adolescent and adolescent children. Thus, it may be the combination of a

developing self-other mapping system and a muted self-perception that contributed to the lack of

body-part mapping in the 7 to 9 year old group.

3.2 Limitations

Limitations of the present study may include a limited amount of trial presentations for

both the spatial and body-part compatibility tasks. Specifically, for the spatial compatibility task,

3 instances of each of the 8 image combinations were presented. Due to the limited amount of

sample data, an outlier procedure was not conducted. Thus, any deviations in attention could

have biased the mean RTs for a particular trial type. Further, any response errors would

significantly reduce the data sample, thus placing significantly more weight on the remaining

viable trials. The range of standard deviations for the spatial compatibility task was between 38-

263 ms. Similarly, with the presentation of the body-part compatibility trials, 5 instances of each

of the 24 image combinations were presented. Thus, eliminating wrong response errors and data

through an outlier procedure limited the amount of interpretable data. The range of standard

deviations for the body-part compatibility task was between 20-170 ms. Thus, the range of

standard deviations for the body-part compatibility task was smaller than that of the spatial

compatibility task. Although this limited number of trial numbers was chosen to keep the time of

testing to a reasonable level and maintain data collection integrity by avoiding fatigue and

boredom, future work could include additional trial numbers.

Another limitation was that only one image per age condition was presented. Thus, it is

possible that no body mapping could occur because of an idiosyncratic feature in the specific

image that was chosen. This may be particularly true for the image of the 7 year old model in

which no body mapping was seen with any of the groups. Future work could include more than

one image per age condition.

Moreover, the age of the model used to represent the 7 to 9 year old age group is on the

lower end of the age range and may not accurately represent the mean of that age group. A one-

42

sample t-test was conducted to determine whether the age of the 7 year old model was

significantly different from the mean of the 7-9 year old age group. The analysis revealed that

the age of the model was significantly different from the mean of the age group, t(12) = 5.11, p<

0.001. Similar analyses performed with the other groups revealed that the age of the model for

which each group demonstrated a compatibility effect was not different from the age of the

groups: 11 year old model for the10 to 12 year old group, t(13) = -0.69, p= 0.50 (Figure 3.2); 15

year old model for the 13 to 16 year old group, t(13) = -1.07, p= 0.30 (Figure 3.3). Although it is

possible that the difference in age between the model and the participants is a factor that led to

the breakdown in self-other matching, inspection of the distribution scores of the three 7 year old

participants’ in that group revealed that these individuals are part of the overall distribution.

Thus, it appears unlikely that a discrepancy between the ages of the7 year old model and the

participants in the 7 to 9 year old group was the leading factor that led to the absence of a body-

part compatibility effect in the 7-9 year old age group (see Figure 3.1).

Figure 3.1. Difference scores of the incompatible by compatible conditions as a function of

model type for the 7 to 9 year old group. Conference Intervals are depicted. Black dots indicate

the three 7 year old participants’ scores.

43

Figure 3.2. Difference scores of the incompatible by compatible conditions as a function of

model type for the 10 to 12 year old group. Conference Intervals are depicted.

Figure 3.3. Difference scores of the incompatible by compatible conditions as a function of

model type for the 10 to 12 year old group. Conference Intervals are depicted.

Additionally, the inclusion of an adult model and adult participants could have provided

additional insights and a clearer picture of interpersonal body representation. In particular, by

having adult participants respond to both the images of the children and of an adult model, one

could investigate whether age specific body-part mapping also occurs with adult interactions.

More importantly, one could explore whether age specific effects are specific of pre-adolescent

44

and adolescent groups or whether this age specific effect also applies to adult and older adult

groups and thus occurring with most age groups.

Another potential limitation of the present study is its cross-sectional design because this

type of design is one of the weakest developmental designs. Cross-sectional studies provide a

'snapshot' of the outcome and the characteristics associated with it, at a specific point in time.

This ‘snapshot’ is limited because it provides information about individuals at a specific point in

time and differing results may emerge if a different time-frame is chosen. Specifically, cross-

sectional designs may be susceptible to cohort effects which make it particularly difficult to

separate effects of developmental changes from cohort effects when examining age effects across

a wide range of ages. This limitation makes interpreting results particularly difficult as cross-

sectional designs are not able to track changes in social processes over time and individual

changes in development. Following the same group of participants over multiple time points in

their lives, as in a longitudinal design, would elevate such effects and allow for the assessment of

developmental trends over time.

On a final methodological note, the newer two-choice hand response task for testing

body-part matching was employed for the present study, substituting the previous technique of

recording foot and thumb responses (e.g., Bach et al., 2007; Welsh et al., 2014; Jovanov et al.,

2015; Pacione & Welsh, in press). Although the patterns of results in earlier work (e.g., Bach et

al., 2007; Welsh et al., 2014; Jovanov et al., 2015; Pacione & Welsh, in press) suggest that the

previous technique of using a foot and thumb responses is sensitive to body part matching

processes, co-occurring vertical spatial compatibility may always present a challenge and

potential confound to interpreting body-part compatibility effects. Using a choice hand response

eliminated the possibility of vertical influence because the responding hands of the participants

are situated at the same elevation in real space, excluding any differences in elevation that were

seen with responses with the foot pedal and thumb plunger. With a choice hand response task,

spatial left-right compatibility effects are likely to be observed, but these left-right spatial

compatibility effects are not relevant because these spatial compatibility effects are orthogonal to

the body-part coordinates. That is, the spatial coordinates between the critical body-part target

conditions (hand/foot) are vertical, whereas the co-occurring spatial dimension is horizontal and

should be more independent of any body-part coding. One potential limitation of this new

choice-hand approach is that the explorations of body-part matching are essentially restricted to

45

the upper-limb. Although studies employing the upper-limb matching procedure are sufficient

for a number of experimental and theoretical contexts, such as animal-human upper limb

matching (Pacione & Welsh, in press) and perhaps tool-embodiment (Jovanov et al., 2015), this

constraint might limit investigations of a wider range of phenomena and matching of multiple

body parts within a single design.

3.3 Future Directions

The body-part compatibility task is an effective tool to assess self-other matching and,

potentially, the involvement of the human body schema in social cognitive processes. It is

thought that the processes that lead to the body-part compatibility effect are those that support

the human ability to empathize with, mimic, and understand the actions of other humans because

it involves the matching of the body parts of others to the representation of the body of the self.

Thus, the body-part compatibility task can be used to assess deficits in self-other matching in

clinical populations, in particular Autism Spectrum Disorder (ASD).

ASD is clinically defined as a triad of impairments in social interaction, communication,

and behavioural flexibility (American Psychiatric Association, 1994). Some of the interpersonal

impairments include difficulties developing a conceptual representation that encompasses the

mental states of others (Theory of Mind) and engaging in shared attention and emotional

engagement with other individuals (Rogers & Pennington, 1991; Williams, Whiten, Suddendorf,

& Perrett, 2001; Smith & Bryson, 1994; Williams, 2008). Autism can be further characterized at

the motor level, with accounts of repetitive and stereotyped behaviour (Williams et al., 2001).

Specifically, persons with autism consistently exhibit problems with mental flexibility and

planning. For example, persons with autism perform like their peers when a task involves

concrete planning, however, more abstract planning behaviours pose a particular challenge

(Glazebrook, Elliott, & Szatmari, 2008). Thus, analyzing deficits associated with action

understanding may correlate with prominent social impairments seen in individuals with autism.

In exploring such potentials, a future study can be employed to investigate the integrity of

mechanisms underlying the ability to represent the bodies of other humans (i.e., self-other

matching) in individuals with ASD by comparing the performance of TD and those with ASD

individuals using the human body-part compatibility task. This information can be used to

understand the neural underpinnings of how one’s own body position influences one’s perception

46

of others’ body representations. The knowledge can be used to identify areas of dysfunction in

ASD.

It is thought that an impaired formation/organization of self-other representations’ may

be at the centre of many of the impairments associated with autism (Williams et al., 2001;

Stewart et al., 2013; Smith & Bryson, 1994; Rogers & Pennington, 1991). Based on the cognitive

profile associated with ASD, and in particular challenges in imitation and theory of mind, it has

been suggested that these impairments seen in individuals with ASD may be related to an

inability to relate perceived limb movements of another individual to executed limb movements

by one’s self, highlighting a self-other mapping or action observation/mirror neuron system

impairment as one of the main possible causes of the deficit (Stewart et al., 2013). Rogers and

Pennington’s (1991) Intersubjectvity Theory suggests that it is this impaired self-other matching

process in individuals with ASD that results in a cascade of impaired capacities including

imitation, emotion-sharing, joint attention, theory of mind, and pretend play.

In designing this future study, the TD participants from the current study and an ASD

group would be matched based on sex, chronological age and non-verbal IQ. The task and design

of the experiment would be based on the current study, where the ASD children would be

responding to the same 3 human male figures – an adolescent aged 15, a child aged 11, and a

child aged 7 - as those presented to the TD participants in the present study. If the children in the

ASD group are able to represent the bodies of others, then that would suggest that limb mapping

is intact and an additional element associated with imitation and action observation may be

impaired. Thus, it may be that the interaction of neural networks associated with limb mapping

and action understanding are compromised. In addition, it could be postulated that motion

detection is a more complex task, reflecting an array of neuronal inputs and therefore additional

areas of possible deficiency. If, however, compromised body-part compatibility effects are seen

in the ASD group, than that would suggest that body mapping is impaired. Such a finding would

suggest that individuals with autism are not able to map the body parts of other individuals onto

their own body schema. This impairment would be reflected in imitation and action observation

deficiencies because, presumably, one needs to understand and match the body parts of others to

the representations of homologous body parts of the self to enable efficient imitation. Therefore,

the imitation impairments seen in individuals with ASD confirm an inability to relate perceived

47

limb movements of another individual to executed limb movements by one’s self, reinforcing a

self-other mapping impairment as a possible cause of the deficit.

3.4 Delimitations

A key factor in making the present work achievable was governing the duration of the

present study in order to maintain the attentional focus of the participants, in particular, the

participants in the youngest age group. Specifically, trial numbers for both the pre-test and test

phases were reduced to facilitate the most accurate responses. The trial blocks were designed to

be completed within a feasible about of time (2-5 minutes), hoping to keep the attentional focus

of the participants on the task. Additionally, the experimenter advanced the “READY” cue for

each trial when she was confident the participant was focused on the task and ready to complete

a trial. Rest and refocusing breaks were strongly encouraged between blocks, ensuring the

participants were refocused when returning to the study.

Additionally, the original design of the study included a 4th

model type representing a

young adult. With the addition of this extra model type, it had increased the amount of blocks

and trials presented which made the study duration exceedingly long and unworkable.

Proceeding with only 3 model types provided the most appropriate alternative. Overall, the study

duration was limited to a maximum 45 minute single session, to ensure that the participants, in

particular the youngest participants, could maintain their focus and attention on the relevant task.

48

Chapter 4 Conclusion

The purpose of the present study was to investigate the integrity of mechanisms

underlying the ability to represent the bodies of other humans (i.e., self-other matching) in

typically developing (TD) children and adolescents. The findings revealed that when viewing

images of children and adolescents with targets placed on homologous body sites of the

observing participant, increased sensitivity of the homologous representation in the human body

schema of the observing child and adolescent will occur. In particular, body-part compatibility

effects were found for both the 10 to 12 and 13 to 16 year old age groups. Most interestingly, the

body-part compatibility effects that emerged for both the 10 to 12 and 13 to 16 year old age

groups occurred when viewing models of their own peers. On the other hand, no body-part

compatibility effects were found for the 7 to 9 year old age group when viewing any of the three

model types.

The results of the present work support the idea that children and adolescence are able to

register the bodies of other children and adolescents, creating a shared neural representation

between the self and other. This shared representation is thought to enable individuals to

represent their own and others’ goal-directed actions via a single conceptual system (Decety &

Sommerville, 2003). This conceptual system would allow individuals to understand the actions,

emotions, and intentions of others. Further, facilitated identification with one’s peer may be a

reflection of shared neural representations between the self and other, where the body of one’s

peer is experienced as something analogous to one’s own experienced body. Thus, individuals

are drawing on information from the structure and movements of their own body to interpret

their environment and shape their cognitive processes. Ultimately, such experiences are likely to

be involved in the ability to understand the actions of others and engagement in social

interaction.

In concluding, the present work provides some initial insights into peer-to-peer

interactions. Specifically, strong resonance with the bodies of one’s peers may be an important

platform on which multiple aspects of social and cognitive development may be built. Indeed,

embodiment is at the heart of action understanding and social interaction. Thus, the potential

implications of these findings may highlight peer interactions as an invaluable source of learning

49

for children and adolescents in school environments. Peers may not provide the same kind of

structure and support during social interactions that are provided by adults, however, the

relevance of peers for early social cognitive development may be understated. Further, these

findings may highlight implications for understanding ASD and other cognitive disorders.

Specifically, impairments associated with self-other matching with one’s peer may be central to

many of the deficits seen in individuals with ASD, including imitation, action observation and

emotional sharing. The knowledge gained can be used to create specialized programs that focus

on building interpersonal skills, with a special emphasis on peer interactions.

50

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