· Web viewDivision of Neuroscience and Experimental Psychology, University of Manchester Gowen, Emma Division of Neuroscience and Experimental Psychology, University of Manchester

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Visual-tactile selective attention in autism spectrum condition: an increased influence of visual

distractors

Running head: Visual-tactile selective attention in autism

Poole, Daniel

Division of Neuroscience and Experimental Psychology, University of Manchester

Gowen, Emma


Warren, Paul A.


Poliakoff, Ellen


Corresponding author:

Daniel Poole

Division of Neuroscience and Experimental Psychology,

University of Manchester,

Oxford Road,

M139PL

[email protected]

Word count = 10,186

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We have previously observed that participants with autism spectrum condition (ASC) are more

influenced by visual distractors during a tactile task compared with controls (Poole, Gowen, Warren,

& Poliakoff, 2015). This finding suggests that changes in multisensory processing could underpin

differences in sensory reactivity in ASC. Here we explore the cognitive mechanisms underlying this

effect. Adults with ASC (n= 22) and matched neurotypical (NT) controls (n= 22) completed three

tasks involving similar stimuli. In Experiment 1, we again showed that when participants with ASC

were performing a tactile task they were distracted more by visual stimuli compared to NTs. In

Experiment 2, however, no differences between the groups were observed on an alternative visual-

tactile task (temporal order judgment) requiring attention to both the stimuli. That is, ASC

performance was typical when the task did not require the visual stimuli to be suppressed.

Furthermore, in Experiment 3 the effects of visual distractors were comparable between the groups

when the tactile target was replaced with a visual target. When comparing performance across

Experiments 1 and 3, NT participants were better able to suppress visual distractors when the target

was tactile than when the target was visual (Experiment 1 versus 3), but this crossmodal benefit was

not observed in participants with ASC. The effects of visual distractors were comparable regardless

of the target modality suggesting that the efficacy of visual-tactile selective attention may be

reduced in ASC.

Keywords: Visual-tactile, autism spectrum condition, selective attention, crossmodal, distractor

interference.

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‘I still can’t even tell when I’ve stepped on someone’s foot or jostled someone out of my way. So, something connected with my sense of touch might be mis-wired too’

Naoki Higashida, an autistic author (Higashida, 2013,The Reason I Jump, pg16)

Autism Spectrum Condition (ASC) refers to a class of neurodevelopmental conditions which are

diagnostically characterised by impairments in social interaction and communication plus restricted

or repetitive patterns of behavior (DSM-V; American Psychiatric Association, 2013). Differences in

sensory reactivity are also experienced by up to 92% of persons with ASC (Green, Chandler,

Charman, Simonoff, & Baird, 2016). These include hypersensitivity, hyposensitivity and sensory

seeking behaviors in response to everyday stimuli (Hazen, Stornelli, O’Rourke, Koesterer, &

McDougle, 2014; Lane, Young, Baker, & Angley, 2010). Hypersensitivity describes an excessive

negative association with stimuli, for example, an extreme sensitivity to the feeling of tags within

clothing, while hyposensitivity describes the apparent unresponsiveness to particular stimuli, for

example having a very high threshold for pain. Sensory seeking behaviors refer to an excessive

interest in sensory stimulation, for instance exploring inedible items in the mouth. These differences

in reactivity occur within, and across, multiple sensory modalities (Kirby, Boyd, Williams, Faldowski,

& Baranek, 2016; Kirby, Dickie, & Baranek, 2014).

Perception of our surroundings involves receiving information via multiple sensory channels (e.g.

vision, touch, hearing). Experimental studies in neurotypical (NT) participants have shown

enhancements in performance with crossmodal compared to unisensory stimuli. For instance,

simple response times (RTs) to crossmodal stimuli are typically faster than the RT to either single

modality (race model violations; Miller, 1982; Molholm et al., 2002). It is also possible to selectively

attend to a sensory modality. When a particular sensory modality is attended to, target stimuli which

appear within that modality are processed more effectively. This has been observed through faster

RTs to stimuli when a target on the preceding trial appeared in the same modality (Miles, Brown, &

Poliakoff, 2011; Spence, Nicholls, & Driver, 2001). Conversely, RTs are increased when targets

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appear in different modalities across trials, reflecting a relative cost of switching attention between

the senses. Efficient processing of target stimuli also requires the suppression of irrelevant,

distracting stimuli. Findings from several different tasks have previously revealed that responses to

target stimuli can be influenced by task irrelevant distractors presented in a separate sensory

modality. For example, when making judgements about visual stimuli, participants typically report

multiple illusory flashes, when a single light flash is accompanied by multiple beeps (the flash beep

illusion; Shams, Kamitani, & Shimojo, 2000; Shams, Kamitani, & Shimojo, 2002). Similarly, the

influence of visual distractors on tactile judgements has been observed using the crossmodal

congruency task (CCT; Spence, Pavani, & Driver, 1998). When making judgements about the

elevation of tactile vibrations presented to either the index finger (top) or thumb (bottom),

participants typically perform more rapidly and accurately when a task irrelevant visual distractor is

presented at the same (congruent) elevation, while a distractor at an incongruent elevation will tend

to produce more errors and longer RTs (Maravita, Spence, & Driver, 2003; Spence, Pavani, Maravita,

& Holmes, 2004). The congruency effect (CE; difference in performance between the incongruent

and congruent conditions) is typically used as a measure of the influence of the distractors. The

effects of distractors presented in a separate modality are modulated by the spatial and temporal

relationship between the target and distractor. Distractors presented close in time and/or space to

the target are more likely to influence the participant’s response whereas distractors that are

presented at an increased stimulus onset asynchrony (SOA), or increased spatial discrepancy from

the target are more easily suppressed (Hairston, Hodges, Burdette, & Wallace, 2006; Shams et al.,

2002; Shore, Barnes, & Spence, 2006; Spence, Pavani, & Driver, 2004; Wallace et al., 2004).

A number of studies have indicated that aspects of multisensory processing may be altered in ASC.

Children with ASC report the illusory flash-beep percept less frequently than controls (Stevenson et

al., 2014; although see Keane, Rosenthal, Chun, & Shams, 2010; van der Smagt, van Engeland, &

Kemner, 2007 for contradictory findings in adult groups). Similarly, for simple RTs to auditory, visual

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and auditory-visual stimuli, performance enhancements in the crossmodal condition were not

observed in children with ASC (Brandwein et al., 2013). ERP recordings in this study also suggest that

children with ASC integrated the auditory-visual stimuli more slowly. These studies imply that

auditory-visual interactions are reduced and less effective in individuals with ASC. Further

differences have been reported in children with ASC relative to controls, when the temporal

discrepancy between auditory-visual stimuli has been manipulated (see Stevenson et al., 2015 for a

recent review). For instance, when presented with task irrelevant auditory stimuli during visual

judgements, children with ASC produce responses consistent with multisensory interactions over a

range of SOAs double in size to NT controls (Foss-Feig et al., 2010; Kwakye, Foss-Feig, Cascio, Stone,

& Wallace, 2011). This suggests that they are less effective at suppressing crossmodal distractors

that are distant in time; that is they show less temporal modulation than NTs (although see de Boer-

Schellekens, Keetels, Eussen, & Vroomen, 2013; Poole, Gowen, Warren, & Poliakoff, 2015, for

contradictory findings for auditory-visual and visual-tactile interactions respectively).

If the interaction between auditory-visual stimuli is reduced and the processing of extraneous stimuli

is not effectively modulated or inhibited, this is likely to alter the sensory and perceptual experiences

of individuals with ASC. Previous work which has explored crossmodal processing in ASC has tended

to focus on auditory-visual interactions. Auditory-visual processing is associated with the production

and comprehension of speech (Stevenson, Zemtsov, & Wallace, 2012) and it has been suggested that

differences in ASC are directly related to impairments in social interaction and communication

(Stevenson et al., 2017). The interaction between the other sensory modalities have received less

research interest, but are also likely to impact on experiences commonly reported in ASC. For

instance, the interaction between visual and tactile information may contribute to differences in the

experience of touch in ASC (see Poole, Gowen, Warren, & Poliakoff, 2016). The act of touching, or

being touched, typically involves both somatosensory and visual information. The atypical

experience of touch commonly reported in ASC (Leekam, Nieto, Libby, Wing, & Gould, 2007) could

be a consequence of discrepancies in how this multisensory information is processed. If the

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experience of touch is affected (Deschrijver, Wiersema, & Brass, 2016), then this could lead to an

avoidance of interpersonal touch which plays an important role in social interaction and particularly

in early social development (see Gallace & Spence, 2010). Furthermore, atypical motor control in

ASC, particularly in the interaction with objects, may be influenced by differences in visual-tactile

processing (Gowen & Hamilton, 2013). The interaction between vision and touch in ASC has been

explored using the rubber hand illusion (Botvinick & Cohen, 1998). If an artificial hand is touched in

synchrony with the participant’s own hand, which is positioned out of view, then the participant

typically experiences illusionary ownership of the rubber hand. The experience of this illusion

appears to be reduced or delayed in children with ASC (Cascio, Foss-Feig, Burnette, Heacock, &

Cosby, 2012; Greenfield, Ropar, Smith, Carey, & Newport, 2015), which might suggest at an atypical

interaction between visual and tactile information, similar to that observed for auditory-visual

interactions. However, as these studies used socially salient stimuli (an artificial hand) it is also

possible that these effects were confounded by reduced attention to social stimuli in ASC (Dawson,

Meltzoff, Osterling, Rinaldi, & Brown, 1998; Dawson et al., 2004).

An alternative approach to characterising visual-tactile processing is to make use of visual-tactile

experiments involving low-level stimuli with no social relevance. In a previous study we explored the

spatial modulation of visual-tactile interactions in a group of adults with ASC (Poole et al., 2015).

Participants completed an adapted version of the CCT, judging whether a tactile vibration was single

or double. Target stimuli were presented around each participant’s tactile temporal acuity threshold,

which allowed tactile performance to be constrained between (and within) the participant groups

before introducing distracting stimuli. This approach is particularly important for heterogeneous

populations such as ASC (see Poole, Couth, Gowen, Warren, & Poliakoff, 2015). Participants were

presented with task-irrelevant visual distractors which could be congruent (single vibration, single

flash) or incongruent (single vibration, double flash). Distractors were next to the stimulated hand

(0cm), 21cm and 42cm from the hand in the same hemispace, and in a location 42cm from the hand

in the lower visual field in the opposite hemispace. NT participants exhibited a significant

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interference effect for distractors presented close to the hand (0cm, 21cm), replicating previous

findings using different versions of this task (Holmes, Sanabria, Calvert, & Spence, 2006; Spence et

al., 2004). Participants with ASC also showed this effect when the visual distractor was presented

42cm from the stimulated hand in the opposite hemispace, suggesting that they were less able to

suppress the processing of distant distractors. That is, the ASC group exhibited reduced spatial

modulation of visual-tactile interactions.

The previously observed finding of reduced spatial modulation of visual-tactile interactions in ASC

(Poole et al., 2015) may have been the result of differences in visual-tactile processing, or less

effective attentional control. In the current work, we developed a series of experiments using closely

matched stimuli to elucidate the cognitive mechanism(s) underlying this effect. In Experiment 1, we

attempted to replicate our previous findings using the adapted version of the CCT with fewer

distractor locations to discount the possibility that the effect was driven by task complexity rather

than a genuine difference in visual-tactile processing. In Experiment 2, participants completed an

alternative visual-tactile task (temporal order judgement) which required attention to both the visual

and tactile stimuli to explore whether differences would extend to general visual-tactile processing,

or were specifically driven by difficulties in suppressing crossmodal distractors in ASC. In Experiment

3, participants completed a purely visual version of our adapted CCT to explore whether group

differences resulted from a reduced ability to suppress distracting visual information, or were

specifically driven by issues in suppressing task irrelevant information when target-distractor pairs

were presented crossmodally.

Aims and Hypothesis

In Experiment 1, we sought to reinforce our previous findings and show that a visual stimulus was

more distracting for ASC participants using a simplified version of the same task. Poole et al. (2015)

presented participants with visual distractors from four different spatial locations. For both groups,

the CEs for distractors from all locations were high and variable. It is therefore possible that the

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observed effect was a consequence of sampling error produced by the variability in the data

resulting from multiple distractor locations. In Experiment 1, we repeated our previous study using

only the distractors presented at 0cm (near) and 42cm from the hand in the opposite hemispace

(far). We anticipated that presenting fewer distractor locations might reduce the variability in

performance that was observed for both groups when distractors were presented from multiple

locations. The NT participants were expected to show increased influence of the distractor in the

near condition in comparison to the far. Following Poole et al. (2015), it was expected that for

participants with ASC the interference effect of distractors would not differ between the near and

far condition.

Method

Participants

Adults with ASC (n= 22) and NT controls (n= 22) matched for age, IQ, gender and handedness took

part in all experiments. Participant characteristics are presented in Table 1. The intended sample size

was 20 participants in each group based on a power analysis from a previous study (β = 0.84. Poole

et al., 2015) with two additional participants to mitigate against participant exclusion. Participants

were recruited through advertisements in the local community, the Autistic Society Greater

Manchester, Tameside Autism Network and SalfordAutism. Diagnosis was confirmed using module 4

of the Autism Diagnostic Observation Schedule (ADOS-2; Lord et al., 2000) by a certified assessor. To

characterise autistic traits in our NT sample, participants completed the Autism Spectrum Quotient

(AQ; Baron-Cohen, Wheelwright, Skinner, Martin, & Clubley, 2001). The AQ is a 50-item Likert

questionnaire designed to measure autistic personality traits where higher scores indicate more

autistic traits and scores over 32 are believed to indicate clinical significance. Two participants did

not complete the AQ. Three participants with ASC and three controls were left handed measured

using the Edinburgh Handedness Inventory (EHI, Oldfield, 1971). All participants had normal or

corrected to normal vision (6/6 vision in both eyes as measured using Snellens test of visual acuity),

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60s arc stereo acuity as measured using the TNO test and no red-green perception deficiencies

(Ishihara, 1979). Exclusion criteria included neurological or psychiatric conditions (apart from autism)

and, of the control group, no first-degree relatives with a diagnosis of autism, elicited via self-report.

To confirm differences in sensory reactivity in our ASC sample, all participants completed the

Glasgow Sensory Quotient (GSQ; Robertson & Simmons, 2013). The GSQ is a 42 item Likert

questionnaire designed to assess sensory differences in adults with ASC. The GSQ investigates hyper

and hypo functioning across a number of sensory modalities.

All participants gave written consent and the study was approved by the University of Manchester

ethics committee in accordance with the Declaration of Helsinki. Participants completed the ADOS,

questionnaires and WASI in a preliminary session. They then completed two separate experimental

sessions. In ‘session A’ participants completed Experiment 1 and then Experiment 3. In ‘session B’

participants completed Experiment 2. The order of the experimental sessions was counterbalanced

within participant groups.

Table 1 Participant characteristics for Experiments 1, 2 and 3. Mean values ± SD. Asterisks denote statistically significant differences (Bonferroni corrected, α = .013)

ASC (n = 22) NT (n = 22) t (42) p

Age 30.90 ± 7.99 31.05 ± 8.71 .02 .985

FSIQ 118.09 ± 9.63 112.18 ± 7.56 1.49 .147

AQ - 16.67 ± 6 - -

ADOS 8.30 ± 2.23 - - -

GSQ score Total 77.52 ± 22.15 32.32 ± 16.77 7.60 <.001*

Hyper sensitivity 37.74 ± 11.12 15.27 ± 7.91 5.99 <.001*

Hypo sensitivity 39.91 ± 13.36 17.04 ± 9.93 7.33 <.001*

Apparatus

Participants sat at a desk in a dimly lit room and were instructed to focus on a central fixation point,

consisting of a white cross (19 mm) on a computer monitor, displayed approximately 30° below eye

level and 45 cm from the participant.

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Participants held a 70mm foam cube between the thumb and forefinger of their dominant hand into

which was embedded a bone conductor (Oticon Limited, B/C 2-PIN, 100Ω, Hamilton, UK), which was

driven by sound files (white noise, ∼66 dB sound pressure level) to create the tactile vibration. The

participant’s index finger was attached to the bone conductor with double-sided adhesive tape. A

black cardboard shield surrounded the monitor and was embedded into the foam cube, concealing

the participant’s index finger from view. A 10mm LED positioned directly above the bone conductor

was visible through a 10mm hole in the shield (the ‘near’ condition). This created the impression

that the light was emitted from the tip of the participant’s finger (see Figure 1). An identical LED was

visible through the shield in the contralateral hemispace, 42cm from the participant’s stimulated

hand (the ‘far’ condition). Each LED was positioned 26.5cm from the central fixation point. All stimuli

were controlled using E-Prime 1.2 software (Psychology Software Tools, Pittsburg, PA).

[FIGURE 1 ABOUT HERE PLEASE]

White noise (~75dB SPL) was played through headphones throughout the experiment to prevent the

participant from hearing sounds emitted by the bone conductor.

Design and Procedure

Participants completed a 2IFC adaptive staircase procedure to approximate their tactile temporal

threshold. Target stimuli were then presented at the participant’s threshold during the experiment

(see Poole et al., 2015).

Threshold Procedure

Before beginning the experimental procedure an adaptive staircase procedure (PEST; see Taylor &

Creelman, 1967) was used to determine the duration required between two vibrations for the

participant to correctly identify a double pulse 75% of the time. This was used to set the level of the

tactile stimuli for the experimental procedure. Participants received two successive tactile stimuli

presented in a random order in a two-interval forced choice procedure; a constant (single) vibration

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and two separate (double) 80ms vibrations separated by a 0–200ms gap. There was a pause of

500ms after the presentation of the first vibration and the order (single or double vibration first) was

randomised. The overall durations of the single and double stimuli were matched. A break was

included after 50 trials and the procedure was capped at 100 trials. If a threshold had not already

been determined by the end of the procedure the threshold was taken as an average of the steps

between the 80th and 100th trial (11 participants with ASC and 9 NT participants). All participants

performed between 60-90% accuracy across these final 20 trials. For 5 participants with ASC and 5

NTs the difference between the step on the 80th and 100th trial was < 10ms suggesting that the

procedure had stabilized close to the participant’s threshold. As only an approximate threshold was

required to set the level of the stimuli for the experimental task, the remaining participants also

continued to the practice procedure where performance accuracy was confirmed (see below).

Experimental Procedure

Participants were asked to make speeded responses upon the presentation of a target vibration.

These target stimuli were either a single or double vibration at the participant’s previously

determined threshold level. Participants responded by lifting their toe in response to single pulses

and their heel in response to double pulses. The task included both touch alone baseline trials and

trials with task irrelevant distracting LED light flashes, which were either congruent (e.g., single

vibration, single light flash) or incongruent (e.g., single vibration, double light flash). The instructions

to participants were: Pay attention to the vibration and respond (single versus double) accurately and

quickly. Focus your eyes on the cross in the middle of the screen throughout the experiment and try

to ignore the light flashes as much as possible; these are intended to distract you.

The distracting light flashes were presented 30ms prior to the tactile target. Previous work has

indicated that the effects of the distractors are greatest at this SOA (Spence, Pavani, & Driver, 2004).

For single flashes the LED was illuminated for 80ms, while double flashes comprised two single 80ms

flashes separated by 120ms. If the participant responded before the presentation of the vibration,

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the trial was discounted and the error message ‘Too early’ was presented for 1000ms. There was an

inter-trial interval of 1500ms following the participant’s response. The central fixation cross

remained onscreen throughout the experimental procedure.

There were five conditions: Distractors (congruent, incongruent) x Location (near, far) plus baseline

trials. Each condition was randomly presented ten times in each block, with half of these trials being

single vibrations and half double. The experiment consisted of four experimental blocks of 50 trials.

The 200 trials comprised 40 congruent and 40 incongruent trials in each of the two locations, plus 40

baseline trials.

Before the experimental procedure began, there were two practice blocks to familiarise participants

with the task and ensure that the threshold procedure had determined an appropriate threshold for

the experimental task. In the first block, participants completed five trials with the gap duration set

at 200ms to ensure that they understood the task instructions. To proceed to the second block they

were required to perform no worse than 80% accuracy. In the second block, participants completed

28 trials: 20 baseline trials and 8 trials with light flashes, four in each condition with each

combination of congruent/ incongruent trials with single/double pulses. If participants did not

perform at 75% accuracy ±10% in baseline trials on this block then the gap duration was increased or

decreased by 1ms before beginning the experimental procedure (5 participants with ASC and 9 NT

participants). If performance accuracy was 100%, or at 50% or below, then the participant repeated

the threshold procedure (1 participant with ASC).

The entire procedure lasted approximately 45 minutes in total and was completed in a single session

prior to Experiment 3.

Analysis

Tactile thresholds were compared between the groups using an independent samples t-test.

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Performance accuracy was calculated for each participant in each condition.1 Participants who

performed at greater than 95%, or below 55%, baseline accuracy were excluded prior to analysis

(one participant with ASC and one NT). After removing these participants, the groups were still

matched on age (ASC = 30.52 years ± 7.97, NT = 30.19 years ± 7.69; t (40) = 0.14, p = .891) and FSIQ

(ASC = 118.60 ± 9.60, NT = 115.80 ± 10.55, t (40) = 0.90, p = .372). Response times longer than

2000ms (ASC 8.31% of all trials; NT 4.94%), or under 150ms (ASC 3.19%, NT 4.94%) were removed

from analysis. These errors were likely caused by lapses in attention, anticipation of the target or

foot pedal errors and were not included in the error rate.

Error rates were used to calculate the CE by subtracting the errors in the incongruent condition from

the congruent condition. A mixed ANOVA was used to compare the CE between the groups and each

distractor location. Significant effects and interactions were followed up with t-tests. Confidence

intervals around all effect sizes are reported (Lakens, 2013). We additionally calculated the Bayes

Factor using JASP (JASP Team, 2016) with the default prior setting. The Bayes Factor (BF10) expresses

the relative evidence in support of the alternative hypothesis compared to the null hypothesis given

the observed data. BF10 ≥ 3 suggests increasingly strong evidence in favour of the alternative

hypothesis, while BF10 ≤ 0.33 suggests increasingly strong evidence in favour of the null. When BF10 =

1 the data does not support either hypothesis (Dienes, 2014). Bayesian statistics are particularly

informative in exploring the extent to which data support the null hypothesis, which is not possible

using frequentist statistics.

To explore facilitation and interference effects, error rate in each visual-tactile condition was

compared with tactile alone (baseline) performance for each group using paired sample t-tests

(Poole et al., 2015).

1 This experiment was designed so that the effects of visual distractors would be observed in error data rather than response times (see Poole et al., 2015). Nevertheless, we have included response time data for Experiments 1 and 3 in the supplementary materials.

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Results

Tactile thresholds

Tactile thresholds did not differ statistically between the groups (ASC mean = 24.16ms ± 11.24; NT

mean = 21.83ms ± 13.62; t (40) = 0.61, p = .548, 2.33 95% CI [-5.45, 10.12], d = 0.19 [95% CI -0.43,

0.81], BF10 = 0.35).

Congruency effect

Overall error rate was increased in participants with ASC compared with NT (ASC mean = 33 ± 9.30;

NT mean = 27.05 ± 9.47; t (40) = 2.06, p = .046, 5.96 95% CI [0.10, 11.81], d = 0.64 [95% CI .011 1.25],

BF10 = 1.58). CE data is displayed in Figure 2. Across the groups the CE was increased in the near

condition in comparison to the far indicating that distractors were spatially modulated (near mean =

13.65 ± 14.94, far mean = 8.20 ± 14.32). However, participants with ASC produced an increased CE

(ASC mean = 14.95 ± 17.28, NT mean = 6.90 ± 10.58). This was confirmed using a mixed ANOVA

[Location (Near, Far) x Group (ASC, NT)] which revealed a significant effect of Location (F (1, 40) =

8.79, p = .005, η2p = .180 [90% CI .034, .343], BF10 = 7.76) indicating that the congruency effect was

larger in the near distractor location. There was a suggestive effect of Group (F (1, 40) = 4.08, p

=.050, η2p = .093 [90% CI .000, .245], BF10 = 1.72) indicating that the congruency effect was larger in

the ASC group. The Location x Group interaction did not reach statistical significance (F (1, 40) = .16,

p = .691, η2p =.004 [90% CI .000, .084], BF10 = 0.30) indicating that reduction in the CE between the

distractor locations was statistically comparable between the groups.


Comparisons with baseline performance

Unisensory, baseline performance did not differ between the groups. Error rate in the baseline

condition was larger for the ASC group than the NT group (see Figure 3), although an independent

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samples t-test revealed this difference was not statistically significant (t (40) = 1.21, p = .233, 3.69

95% CI [-2.47, 9.86], d = 0.38 [95% CI -0.25, 1.01], BF10 = 0.54).

To compare facilitation and interference effects in response to visual distractors over unisensory

tactile performance the error rate in each condition was compared with baseline. The ASC group

showed interference effects in both the near and far locations, while the NT group did not show any

significant interference or facilitation effects (see Figure 3). This was confirmed using paired sample t

tests comparing each congruent and incongruent condition with baseline performance reported in

Table 2.


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Table 2. Paired sample t-tests comparing error rate in each condition to tactile alone baseline

condition. Asterisks denote a significant difference from baseline (Bonferroni corrected α = .013).

Baseline vs t (20) p Mean difference [95%CI]

d [95%CI] BF10

ASC Near Congruent -1.30 .210 -3.45

[-9.01,2.10]

-0.28

[- 0.72, -0.16]

0.47

Near Incongruent 4.57 < .001* 13.86

[7.53, 20.18]

0.98

[0.46, 1.51]

159.23

Far Congruent -1.76 .094 -4.88

[-10.68,0.92]

-0.38

[-0.82, 0.06]

0.84

Far Incongruent 3.25 .004* 7.71

[2.76, 12.67]

0.70

[.22, 1.18]

10.90

NT Near Congruent -1.66 .113 -3.69

[-8.34, 0.95]

-0.36

[-0.80, 0.08]

0.73

Near Incongruent 2.32 .031 6.31

[0.62, 11.99]

0.51

[0.05, 0.96]

1.98


[-7.49, 2.96]

-0.20

[-0.62, 0.24]

0.33

Far Incongruent 0.90 .379 1.55

[-2.04, 5.14]

0.20

[-0.24, 0.63]

0.33

Discussion

In Experiment 1, we investigated the influence of visual distractors on a tactile judgement in

participants with ASC and NT controls. Presenting stimuli at threshold level constrained baseline

performance between the groups. The CE was greater in the near distractor location in comparison

to the far, meaning that the visual distractor had a greater influence on participant’s responses to

tactile stimuli when presented next to the participant’s stimulated hand (Holmes, Sanabria, Calvert,

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& Spence, 2006; Poole et al., 2015; Spence et al., 2004). However, the ASC group tended to produce

an increased CE across the locations meaning that visual distractors had a greater impact on ASC

participant’s responses in comparison to the NT group.

When comparing performance in distractor conditions to baseline, different patterns were observed

in each group. NT participants did not display an influence of the distractors on error rate compared

to tactile-alone baseline performance. For participants with ASC, an interference effect was

observed in both the near and far distractor locations. The findings of the present study have

replicated Poole et al. (2015); participants with ASC again produced a significant distractor effect in

both the near and far locations using a simplified design2.

There are a number of explanations of this finding which are explored in the following experiments.

In Experiment 2, an alternative visual-tactile task with no crossmodal selective attention component

was used to explore whether participants with ASC would also perform differently on a visual-tactile

task which did not involve suppressing the visual stimuli.

Experiment 2

Experiment 2 investigated whether the increased distractor effects observed in Experiment 1

reflected a general effect on visual-tactile interactions or was related to the requirement to suppress

the visual distractors. This was achieved by using a crossmodal temporal order judgement (TOJ) task

requiring no crossmodal selective attention component as participants must attend to stimuli in both

modalities. In crossmodal TOJ tasks, participants are presented with stimuli from different modalities

which are separated by a range of SOAs. The participant is asked to judge the order in which the

stimuli were presented and the Just Noticeable Difference (JND; the smallest quantity by which a

stimulus attribute can be increased for the participant to detect a change) can be calculated. This

2 As an additional analysis, the CE produced by the NT participants was pooled across the near and far locations and compared with the performance of the NT participants tested in Poole et al (2015). A between participants t-test revealed the CE was significantly higher in Poole et al (2015), t (23.84) = 2.21, p = .034, d = 0.73, BF10 = 2.10, and the data violated Levene’s test of equal variance (p < .05). This suggests that presenting distractors from multiple locations in Poole et al (2015) inflated the CE and the associated variability.

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JND is used as a measure of the participant’s multisensory temporal acuity where lower JND values

indicate superior temporal acuity. Studies in NTs have previously indicated that visual-tactile TOJs

are improved when the visual stimulus is presented beyond the area of peripersonal space

surrounding the participant’s stimulated hand. For instance, Spence, Baddeley, Zampini, James and

Shore (2003) compared TOJs where the visual stimulus was presented in the same and opposite

hemispace to the tactile stimuli. JNDs were reduced when the visual stimulus was presented in the

opposite hemispace, indicating that participants were better able to reduce the temporal order

when the stimuli were presented at different locations.

Aims and Hypothesis

The visual-tactile TOJ task allows us to explore performance on a task using similar stimuli to

Experiment 1 presented in near and far space without placing demands on the participant’s selective

attention. We predicted that NT participants would show an improvement in TOJs when the stimuli

were spatially separated, which would be observed in reduced JNDs in the far location in comparison

to the near. Furthermore, if differences in visual-tactile interactions in ASC are not specific to

selective attention, then JNDs may be increased and the benefit of spatial discrepancy when making

TOJs may be reduced in comparison to NTs.

Method

Apparatus and Stimuli

The apparatus was identical to Experiment 1 (see Figure 1). However, in Experiment 2 the tactile

stimulus was generated by a different sound file (sine wave, 440Hz, 0.8 AMPs, 8ms in duration).

Design and Procedure

Each trial began with a fixation cross which appeared on screen for an interval randomly selected

from a uniform distribution ranging between 500-1000ms, remaining onscreen as the stimuli were

presented. On each trial, participants received a 8ms tactile vibration and a 8ms light flash using the

19

method of constant stimuli. Stimuli were presented at ± 28ms, 63ms, 98ms, 208ms and 408ms

stimulus onset asynchronies (SOA) where negative SOAs indicate that the visual stimulus preceded

the tactile. Participants were presented with visual stimuli at each SOA in one of 2 conditions: near

and far. The instructions given to participants at the beginning of the experiment were: state

whether you think the flash or vibration was first. Keep your eyes focused on the cross in the middle

of the screen throughout the procedure. On each trial, after the stimuli were presented, an onscreen

prompt appeared reading ‘Was the flash or touch first?’ Participants made unspeeded verbal

responses, which were recorded by the experimenter. There was a delay of 1000ms after the

experimenter entered the participant’s response before the next trial commenced. No feedback was

provided during the experimental trials. The 28ms-208ms SOA trials were each presented 20 times

and the 408ms SOA 8 times for each condition3. Each condition was presented over two blocks of 88

trials, giving 352 trials in total. Participants received alternating blocks of the near and far conditions,

with the starting condition counterbalanced between participants. The locations were blocked to

avoid switching attention between spatial locations trial-by-trial.

Prior to beginning the experimental trials, participants completed a practice procedure of 10 trials

with the light flash presented from the near and far locations at ±408ms SOA. Feedback was

provided in the practice trials, incorrect responses were followed by an ‘incorrect’ sign which was

displayed on screen for 1000ms. Participants continued to the experimental trials once the task

instructions were understood and performance was at least 80% accurate for each condition.

Experiment 2 took place in a single session which lasted approximately 45 minutes.

Data analysis

Responses in each condition were converted to proportion of ‘vibration first’ responses (see Figure

4). Each participant’s data for each condition was then fitted by a logistic psychometric function

3 As in previous studies investigating spatial effects in crossmodal TOJs (e.g. Zampini, Shore and Spence, 2003), the anchor SOA trials (408ms) were included as it was anticipated the judgement would be easy for all participants at this SOA, preventing loss of focus on the task. Responses in the 408ms SOA conditions were not included in the function fitting.

20

using the Palamedes toolbox for MATLAB (Kingdom & Prins, 2009). A measure of function fit (pDev)

to the data was also estimated using the toolbox where values of pDev closer to 1 indicate that the

function better fitted the measured data points. Data for three participants with ASC and four NTs

were removed prior to analysis where functions were poorly fitted (pDev <.05), as suggested by

Kingdom and Prins (2009). The remaining participants included in the analysis did not differ in age

(ASC = 30.42 years ± 7.76, NT = 31 years ± 8.87, t (35) = 0.21, p = .834) or FSIQ (ASC = 117.74 ± 8.19,

NT = 115.11 ± 9.35, t (35) = 0.87, p = .388). Values of pDev for the remaining participants are

included in Table 3.

Table 3. Psychometric function goodness of fit in the near and far locations (mean pDev ± SD).

Values of pDev closer to 1 represent better function fits.

pDev (± SD) Near Far

ASC 0.45 ± 0.31 0.45 ± 0.28

NT 0.55 ± 0.29 0.64 ± 0.22

The slope, β, was extracted from the remaining functions and the JND calculated as 0.675β (Zampini,

Shore, & Spence, 2003a, 2003b). Repeated measure ANOVAs with group as the independent factor

were used to explore whether the JNDs differed between the groups in each condition. Bayes

Factors were also calculated as described in Experiment 1.

Results

For both groups, JNDs were lower in the far condition in comparison to the near, indicating a benefit

of spatial discrepancy (near mean = 41.71ms ± 19.91, far mean = 38.49ms ± 20.36). JNDs across the

locations were comparable between the groups suggesting visual-tactile temporal acuity was similar

for participants with ASC and NT (ASC mean = 38.49 ± 25.94, NT mean = 37.34 ± 12.34). Both groups

showed a similar reduction in JNDs between the near and far conditions (see Figure 4).

21


This was confirmed using a mixed ANOVA [Location (Near, Far) x Group (ASC, NT)] which revealed a

significant effect of Location (F (1, 35) = 11.12, p = .002, η2p = .241 [90% CI .038, .447], BF10 = 18.16)

indicating that the JND was significantly larger in the near location in comparison with the far. There

was no main effect of Group (F (1, 35) = 0.03, p = .856, η2p = .001 [90% CI .000, .034], BF10 = 0.46),

indicating that JNDs were comparable between the groups. Critically, the Location x Group

interaction did not reach significance (F (1, 35) < .01, p = .985, η2p < .001 [90% CI .000, <.001], BF10 =

0.33), indicating that JNDs across the locations was comparable between the groups.

Discussion

In Experiment 2, participants with ASC and NT controls completed a visual-tactile TOJ task in which

the visual stimuli were presented at a location either near or far from the participant’s stimulated

hand. There is evidence that multisensory temporal acuity is reduced in ASC compared with NTs (de

Boer-Schellekens, Eussen, & Vroomen, 2013; Stevenson et al., 2014), although contradictory

findings have been reported in slightly older participant groups (Poole et al., 2016). In the present

experiment the JNDs were comparable between the groups suggesting temporal acuity for visual-

tactile information is typical in adults with ASC (see also Poole et al., 2017).

In line with a number of previous studies, the JNDs of NT participants were reduced when presented

in the far condition over the near condition (e.g. Poliakoff, Shore, Lowe, & Spence, 2006; Spence et

al., 2003). That is, participants showed a benefit of spatial discrepancy on visual-tactile TOJs.

Critically, this effect was observed in both participants with ASC and NTs. This suggests that both

participants with ASC and NT were better able to separate the visual and tactile stimuli in time when

presented in contralateral hemispaces. Note that locations of the near and far conditions were

identical to the distractor locations in Experiment 1, suggesting that there is not a general effect on

visual-tactile processing in ASC across these spatial locations. It is interesting to consider these

22

findings in light of a recent study examining tactile temporal order judgements between the hands

which observed that children with ASC do not produce the typical performance detriment when

their hands are crossed (Wada et al., 2014). Although this is a purely tactile task, the hands crossed

effect has been attributed to the visual frame of reference affecting tactile perception, which might

predict that visual-tactile TOJs would be atypical in the ASC group in Experiment 2. NT children begin

to show the crossed hands effect at around 6 years of age, and the effect is observed in late

blindness, but not in congenitally blind children (Pagel, Heed, & Röder, 2009; Röder, Rösler, &

Spence, 2004). It may be that the representation of visual space becomes more closely mapped onto

somatosensory representations later in development in ASC.

The performance of the ASC group was similar to the NT group on this visual-tactile task (cf., Poole

et al., 2016) which did not require either stimuli to be suppressed (no selective attention

component), suggesting that the increased effect of distractors observed in Experiment 1 was not

due to a general effect on visual-tactile processing. In Experiment 3 we investigated whether the

increased distractor effects in ASC that were observed in Experiment 1 were specifically crossmodal,

or would also be observed on a purely visual version of the CCT.

Experiment 3

In Experiment 3 we explored whether the increased effect of visual distractors in participants with

ASC would also be observed in an equivalent unisensory visual task. There is a substantial literature

suggesting that aspects of visual selective attention may be affected in ASC (for a detailed review see

Ames & Fletcher-Watson, 2010), relating to executive functioning deficits (Hill, 2004; Ozonoff,

Pennington, & Rogers, 1991; Robinson, Goddard, Dritschel, Wisley, & Howlin, 2009). The flanker task

(Eriksen & Eriksen, 1974) is frequently used to investigate distractor interference. Participants are

asked to respond to a target stimulus as quickly as possible. Simultaneous distracting information

flanks the target, which may be either incongruent or congruent with the correct response. RTs are

typically increased in incongruent trials over congruent trials and the size of this effect is a measure

23

of distractor suppression. Children with ASC produce increased RTs on incongruent trials in variants

of the flanker task suggesting that the ability to suppress distracting information is reduced (Adams

& Jarrold, 2012; Christ, Holt, White, & Green, 2007; Christ, Kester, Bodner, & Miles, 2011). Similarly,

participants with ASC also produce more errors on anti-saccade tasks where the participant is

instructed to volitionally direct their gaze, and attention, in the opposite direction to a peripheral

visual distractor (Goldberg et al., 2002; Luna, Doll, Hegedus, Minshew, & Sweeney, 2007; Mosconi et

al., 2009). This suggests that the ability to inhibit the oculomotor response toward distracting visual

information is reduced in comparison to NTs.

Aims and Hypothesis

In Experiment 3, we utilized a visual selective attention task which was closely matched to the

adapted CCT used in Experiment 1 so that we could examine effects elicited by the same visual

distractors when making judgements about a different target. Participants judged whether visual

flashes from a green target LED were single or double, presented at the participant’s previously

determined temporal acuity threshold. Red distractor flashes which could be congruent (single

target flash, single distractor flash), or incongruent (single target flash, double distractor flash) were

presented in positions near and far from the target. The participant’s hand was positioned in the

same manner as Experiment 1 to ensure that the experiments were closely matched. We expected

that controlling hand space in this way would make attention to the target approximately equivalent

to Experiment 1 as attentional resources are typically allocated to the area around the hand (Lloyd,

Azañón, & Poliakoff, 2010; Spence & Driver, 2004) . We anticipated that the CE would be increased

in the near location in comparison to the far for NT participants. If there was a general selective

attention deficit in ASC then the effect of distractors would be increased in comparison to controls

and would not differ between the near and far distractor locations if spatial modulation were

reduced. However, if only crossmodal selective attention was affected then the CE would be similar

to NT participants and reduced in the far location compared to the near.

24

Method

Apparatus

The apparatus was similar to Experiment 1 (see Figure 1b). Participants sat at the same desk as

Experiments 1 and 2, the position of the participant and fixation cross were identical. Participants

were instructed to keep the index finger of their dominant hand in a groove in a 70 mm foam cube

which was positioned behind the cardboard shield which surrounded the monitor. The bone

conductor was removed and a 10mm green LED was included (the target). The target was positioned

directly below the 0cm distractor. This green LED was covered by a plastic filter to approximately

match the luminance (~ 197cd/m2) to the red LEDs (~153cd/m2). The target light could be positioned

in a symmetrical location in the contralateral hemispace allowing identical positioning for left

handed participants.

Procedure

The procedure was similar to Experiment 1.

Threshold Procedure

Participants received two successive visual stimuli in a 2IFC procedure. The visual stimuli were

delivered through the green (target) LED. Stimuli comprised a single visual flash or two 80ms flashes

separated by a gap of 0-200ms. The order of presentation was randomised and the overall duration

of single and double stimuli was matched. The participant was instructed to indicate which interval

contained the double flash using the foot pedal. An adaptive staircase procedure (PEST; see Taylor

Creelman, 1967) identical to the tactile procedure described in Experiment 1 was used to determine

participant visual acuity thresholds. If a threshold had not already been determined by the end of

the procedure then the threshold was taken as an average of the steps between the 80 th and 100th

trial (12 participants with ASC and 13 NT participants). All participants performed between 60-90%

25

accuracy across these final 20 trials. For 7 participants with ASC and 6 NTs the difference between

the 80th and 100th step was less than 10ms suggesting that the procedure had stabilized close to the

participant’s threshold. As only an approximate threshold was required for this study, the remaining

participants also continued to the practice procedure where performance accuracy was reconfirmed.

Experimental Procedure

Participants responded to a green visual target presented at approximate threshold level, lifting their

toe in response to single flashes, and heel in response to double. The task included both baseline

trials and trials with task-irrelevant distracting light flashes delivered from the red LEDs, which were

either congruent or incongruent. For single flashes the red LED was illuminated for 80ms, double

flashes comprised two single 80ms flashes separated by 120ms. The instructions to participants

were: Focus on the green flashes and respond (single versus double) accurately and quickly. Focus

your eyes on the cross in the middle of the screen throughout the experiment and try to ignore the

red light flashes as much as possible; these are intended to distract you.

As in Experiment 1, distractors were presented 30ms prior to the onset of the target (-30ms SOA).

There were 5 conditions: Distractors (congruent, incongruent) x Location (near, far) plus baseline

trials. There were four experimental blocks of 50 trials, in which each condition was presented 10

times in a randomised order. This gave a total of 200 trials, with 40 trials in each condition.

The practice procedure was similar to that described in Experiment 1. Participants first completed 5

trials with the duration of gap set at 200ms. The second practice block featured 28 trials presented

at the participant’s threshold level; 20 baseline trials and eight trials including distractors. If

participants did not perform at 75% accuracy ±10% in baseline trials on this block then the gap

duration was increased or decreased by 1ms before beginning the experimental procedure (6

participants with ASC and 7 NT participants). If performance was at 100%, or at 50% accuracy or

below, then the participant repeated the threshold procedure (2 participants with ASC and 1 NT

participant).

26

The entire procedure lasted approximately 45 minutes in total and was completed in a single session

following Experiment 1.

Analysis

Performance accuracy was calculated for each participant in each condition. Participants who

performed at greater than 95% or below 55% baseline accuracy were excluded prior to analysis (2

participants with ASC and 2 NTs). After removing these participants, the groups were still matched

on age (ASC= 30.95 years ± 7.82, NT = 30.35 years ± 8.44; t (38) = 0.23, p = .817) and FSIQ (ASC =

118.70 ± 9.88, NT = 115.30 ± 10.49; t (38) = 1.05, p = .298). Trials longer than 2000ms (4.27% of ASC

trials, 3.25% of NTs), or under 150ms (1.53% of ASC trials, 3.18% of NTs) were removed from

analysis. The same statistical analysis was used as in Experiment 1.

Results

Visual thresholds

Visual thresholds were statistically comparable between the groups (ASC mean = 29.46 ± 36.90, NT

mean = 17.67 ± 10.69). This was confirmed using an independent samples t-test with equal variances

not assumed (t (22.17) = 1.37, p = .184, 11.78 95% CI [-5.60, 29.18], d = .43 95% CI [-0.20, 1.06], BF10

= 0.65).

Congruency effect

Overall error rate was statistically comparable between participants with ASC and NT (ASC mean =

28.17± 8.98; NT mean = 30.57 ± 8.88; t (38) = -0.85, p = .402, -2.39 [95% CI -8.11, 3.33], d = -0.27

[95% CI -0.86, <.01], BF10 = 0.41). CE data is displayed in Figure 5. For both groups, the CE was

increased in the near condition in comparison to the far indicating that the effect of distractors

differed across locations (near mean = 29.90 ± 16.82, far mean = 20.16 ± 15.92). Both groups showed

a similar reduction in the CE between the two locations and general level of the CE was similar for

both groups (ASC mean = 23.51 ± 17.15, NT mean = 26.61 ± 16.92). This was confirmed using a

27

mixed ANOVA [Location (Near, Far) x Group (ASC, NT)] which revealed a significant effect of Location

(F (1, 38) = 16.28, p < .001, η2p = .300 [90% CI .108, .459], BF10 = 108.12) indicating that the

congruency effect was larger in the near distractor location. There was no significant effect of Group

(F (1, 38) = 0.45, p =.506, η2p = .012 [90% CI .000, .117], BF10 = 0.40) indicating that the size of the

congruency effect was comparable for the ASC and NT groups. The Location x Group interaction was

not significant (F (1, 38) = 0.10, p = .751, η2p =.003 [90% CI .000, .076], BF10 = 0.29) indicating that the

pattern of CE across the distractor locations was statistically comparable between the groups.


Comparisons with baseline

Performance in target alone baseline trials did not differ between the groups. Although error rate in

the baseline condition was greater for the NT group (see Figure 6), an independent samples t-test

revealed no significant difference between the groups (t (38) = 0.20, p = .842, -0.88 95% CI [-9.70,

7.95], d = .06 95% CI [-0.56, 0.68], BF10 = 0.65).


To compare facilitation and interference effects in response to distractors over baseline trials, error

rate in each condition was compared with baseline. Participants with ASC showed significant

facilitation and interference effects in both locations, while the NT group showed significant

interference effects in both locations. This was confirmed using paired sample t-tests comparing

each congruent and incongruent condition with baseline as reported in Table 4.

28

Table 4. Paired sample t-tests comparing error rate in each condition to target alone baseline

condition. Asterisks denote a significant difference from baseline (Bonferroni corrected α = .013).

Baseline vs t (19) p Mean difference [95%CI]

dz [95%CI] BF10

ASC Near Congruent -2.82 .011* -7.50

[-13.64, - 2.01]

-0.63

[-1.11, -0.14]

4.73


[13, 27.40]

1.21

[0.70, 1.91]

1183.21

Far Congruent -4.27 < .001* -11.43

[-15.76, - 5.39]

-0.95

[-1.48, -0.41]

79.51

Far Incongruent 3.08 .006* 9.17

[2.70, 14.14]

0.63

[0.19, 1.17]

7.69

NT Near Congruent -2.30 .033 -10.60

[-17.80, -0.85]

-0.51

[-0.97, -0.04]

1.94


[16.46, 28.69]

1.62

[0.93, 2.28]

57555


[-14.90, -1.84]

-0.60

[-1.07, -0.12]

3.72

Far Incongruent 5.39 < .001* 14.33

[7.92, 17.98]

1.21

[0.62, 1.78]

742

.

Additional analysis: Comparisons between Experiment 1 and 3

As an additional analysis we compared the CE between Experiment 1 and 3, to explore whether

distractor effects depended on whether target-distractors were across vision and touch (Experiment

1) or within the visual modality (Experiment 3). Participants who were not included in the original

analysis of either experiment due to high/low baseline error rate were not included. The remaining

participants included in the analysis (19 in the ASC group, 19 in the NT group) did not differ in age

(ASC = 30.53 ± 7.79, NT = 29.47 ± 7.67; t (36) = 0.42, p = .677) or FSIQ (t (36) = 1.18, p = .246).

29

The CE was larger in Experiment 3 (mean = 24.34 ± 16.40) than Experiment 1 (10.93 ± 15.29). Across

the experiments the CE was larger in the near location (21.67 ± 1.97) in comparison to the far (13.60

± 15.91). Interestingly, participants with ASC did not show as great a reduction in the CE between

Experiment 3 (23.56 ± 16.98) and 1 (15.61 ± 17.86) as was observed in control participants

(Experiment 3, 25.12 ± 16; Experiment 1, 6.25 ± 10.50). CE data is displayed in Figure 7.


A mixed ANOVA [Experiment (Experiment 1, Experiment 3) x Location (Near, Far) x Group (ASC, NT)]

revealed a significant effect of Experiment (F (1, 36) = 23.12, p < .001, η2p = .391 [90% CI .180, .539],

BF10 = 1196000) indicating that the CE was greater in Experiment 3. There was a main effect of

Location (F (1, 36) = 31.11, p < .001, η2p = .465 [90% CI .252, .598], BF10 = 30.33) indicating that the CE

was greater in the near location across the experiments. There was no main effect of Group (F (1, 36)

= 1.25, p = .271, ηp2 = .034 [90% CI .000, .168], BF10 = 0.41) indicating that the size of the CE across

the experiments was similar between the two groups. However, there was a non-statistically

significant trend towards an interaction between Experiment and Group (F (1, 36) = 3.82, p = .058,

η2p = .096 [90% CI .000, .257], BF10 = 6.03) indicating that participants with ASC did not show a similar

reduction in the CE between Experiments 3 and 1 as was observed in NT participants. The interaction

between Location and Group did not reach statistical significance (F (1, 36) = 0.59, p = .447, η2p

= .016 [90% CI .000, .132], BF10 = 0.27), indicating that participants with ASC and NT both produced

reduced CEs between the near and far conditions. Finally, the interaction between Experiment,

Location and Group did not reach statistical significance (F (1, 36) = 0.24, p = .627, η2p = .007 [90%

CI .000, .103], BF10 = 0.33).

Discussion

In Experiment 3 we utilized a novel unimodal task comparable to that reported in Experiment 1 to

explore visual selective attention in participants with ASC and NT controls. The CE was increased in

the near location in comparison to the far for both groups and there were no between group

30

differences. Comparisons of distractor conditions with baseline performance were similar for

participants with ASC and NT. Both groups produced interference effects compared to baseline

performance in both the near and far distractor locations. The findings of Experiment 3 suggest that

the processing of visual distractors is comparable to controls when making judgements about a

visual target. Participants with ASC did not produce the same distractor effects as observed in

Experiment 1 with identical distractor stimuli when the target was visual instead of tactile. A number

of studies which have explored visual selective attention with low-level stimuli have previously

reported an increased influence of distractors on the target for participants with ASC (Christ et al,

2007, 2011, Adams and Jarrold, 2011). However, other studies have reported comparable selective

attention performance with controls (Van Eylen, Boets, Steyaert, Wagemans, & Noens, 2015). It is

worth noting that participants with ASC displayed facilitation effects in both the near and far

locations in Experiment 3, which could reflect a failure of selective attention (this point is discussed

further below). Further research is required to explore the strength of selective attention within the

visual modality, using tightly controlled stimuli, across development in ASC.

As an additional analysis, the CE was compared between Experiment 1 and 3. In Experiment 3

participants were instructed to attend to a stimulus within the same modality (visual) as the

distractors with all other aspects of the task design closely matched to Experiment 1. For NT

participants, interference effects were increased in comparison to Experiment 1 where identical

distractors were used, but the target was presented in a different modality (tactile). There was a

crossmodal benefit to selectively attending to the target, such that the suppression of the distractors

was greater when in a different sensory modality. However, for the ASC group distractor effects

were comparable whether target-distractors were within or across modalities. That is, they did not

show the same benefit of the distractor being in a different modality to the target as NT participants.

As the ASC group produced a comparable pattern of performance to NTs on Experiment 3, the effect

observed in Experiment 1 cannot simply be attributed to any issues with the ASC group

understanding the task instructions or preparing a response using the footpedal. It is worth noting

31

that differences in the perceived timing of the distractor stimuli between Experiments 1 and 3 may

have contributed to the increased distractor effects. In Experiment 1, the visual distractors were

presented 30ms prior to the tactile target as distractor effects are maximal at this SOA (see Spence,

Pavani, & Driver, 2004). The reduced transduction rate of visual information is believed to induce the

perception of simultaneity between visual-tactile stimuli at this SOA. In Experiment 3, we sought to

closely model the procedure of Experiment 1. However, it is possible that the visual distractor was

instead perceived slightly before the visual target, leading to some additional response priming from

the distractor (Schmidt, Haberkamp, & Schmidt, 2011). This additional priming effect may also have

accounted for the facilitation effects observed in both distractor locations for the ASC group.

In Experiment 3, we developed a novel visual selective attention task matched to the CCT. Although

participants with ASC showed some facilitation effects from distractors which were not observed in

NTs, distractor processing was statistically comparable between the groups. Furthermore,

comparisons with Experiment 1 revealed that NT participants showed a crossmodal benefit to

selective attention, that is an increased suppression of visual distractors when the target was tactile,

which was not apparent in the ASC group. This suggests that participants with ASC do not have a

generalized issue with the suppression of distracting visual information and that there may be a

more specific visual-tactile selective attention deficit.

General discussion

The findings of the present investigation can be summarized as follows: adults with ASC exhibited an

increased influence of visual distractors on tactile judgements in Experiment 1 as was previously

observed by Poole et al (2015). However, performance was comparable between the ASC and NT

groups on a visual-tactile task with no selective attention component (Experiment 2). Experiment 3

indicated that the performance of participants with ASC was comparable to controls on a closely-

matched purely visual-selective attention task, suggesting that the findings of Experiment 1 cannot

be attributed to a general issue with suppressing distracting visual information in ASC, or in issues

32

with preparing a motor response using the footpedal. When comparing Experiments 1 and 3, NT

participants tended to show a crossmodal selective attention benefit, such that the suppression of

the distractors was greater when in a different sensory modality. However, for the ASC group

distractor effects were more comparable whether target-distractors were within or across

modalities. That is, we have provided preliminary evidence that they did not show the same benefit

of the distractors being in a different modality to the target as NT participants. Together the findings

of Experiments 1-3 suggest a specific reduction in ability to selectively attend to aspects of visual-

tactile stimuli in participants with ASC.

The influence of visual distractors on the traditional version of the CCT has been attributed to both

basic perceptual processing and higher level response competition (Spence, Pavani, Maravita, et al.,

2004). According to the perceptual processing account, the influence of distractors on performance

is the result of the integration of visual-tactile stimuli, or cueing effects of the distracting visual

stimuli. Alternatively, the response competition account proposes that incongruent stimuli co-

occurring with the target can cause conflict during information processing, leading to an influence on

the participant’s response. Although it is not possible to disentangle the contribution of these

mechanisms using the current design, it seems likely that response competition was driving the

distractor effects here, as the effects of distractors were principally observed in incongruent

conditions. EEG recordings during the traditional version of the CCT have shown an enhanced N2

component is observed prior to the participant’s correct response following incongruent visual

distractors (Forster & Pavone, 2008). Enhanced error related negativity was also observed following

distractor driven incorrect responses. This component is believed to reflect cognitive control relating

to the detection and monitoring of conflict during the task (see Larson, Clayson, & Clawson, 2014).

As reduced adaptation to conflict has previously been observed in the N2 component in children

with ASC (Larson, South, Clayson, & Clawson, 2012), ERPs measured during Experiments 1 and 3

33

could be used to investigate the role of response conflict on ASC participant distractor effects

observed in the current study.

Furthermore, an enhanced perceptual processing capacity in ASC should also be considered in

relation to the present findings. Distractor effects are dependent on available perceptual capacity

after target processing (see Lavie et al., 1995). That is, distractor effects are reduced when the target

is presented at higher levels of perceptual load (e.g. increased set size on a visual search task).

Similarly, when the perceptual load of the target modality is increased, processing of task irrelevant

information in a different modality is reduced (Macdonald & Lavie, 2011; Parks, Hilimire, & Corballis,

2009; Although see Sandhu & Dyson, 2016). Several studies have indicated that individuals with ASC

may have an increased perceptual capacity leading to processing of task irrelevant stimuli at higher

levels of perceptual load (Remington, Swettenham, & Lavie, 2012; Remington, Swettenham,

Campbell, & Coleman, 2009; Tillmann, Olguin, Tuomainen, & Swettenham, 2015). It is possible that

an enhanced processing capacity in the tactile modality may have contributed to increased

distractor effects in Experiment 1, but as perceptual load was not manipulated in the present study

this remains speculative.

To our knowledge, this is the first investigation to highlight a failure of visual-tactile selective

attention in ASC. A recent auditory-visual task has also revealed that distractor suppression across

the senses may be reduced in ASC (Murphy, Foxe, Peters, & Molholm, 2014). Children with ASC

performed a task in which they were cued to attend to target stimuli in either the visual or auditory

modality. The ASC group showed reduced sensitivity to the targets when task irrelevant stimuli in

the non-attended modality accompanied the target. When responding to visual targets, auditory

distractors also caused a significant increase in RTs over unisensory performance in the ASC group.

Furthermore, ERPs revealed that task based modulation of pre-stimulus alpha band activity, which is

believed to reflect anticipatory top-down suppression of distracting information, was reduced. In

34

accordance with the current investigation, these findings suggest that distracting information

presented in a different sensory modality to target information is less effectively suppressed in ASC.

Although further work is required to explore the nature of these effects, previous research has

highlighted that distractor suppression can be improved with training (e.g. Jha, Krompinger, &

Baime, 2007) and may represent a promising approach to ameliorating sensory reactivity in ASC.

The present study sheds light on the cognitive mechanisms that underpin the increased distraction

effects on a visual-tactile task in participants with ASC (Poole et al., 2015). We show that such effects

cannot be attributed to general issues with visual-tactile processing (Experiment 2), or in suppressing

distracting visual information (Experiment 3), and are most likely driven by reduced crossmodal

selective attention in ASC. Further investigation of the mechanisms which underlie atypical

crossmodal selective attention in ASC represent a useful line of enquiry to improve the

characterisation of differences in sensory reactivity in the condition.

Context of the research

This research was conducted as part of the first author’s PhD research project which comprised a

series of experiments investigating aspects of multisensory perception in adults with ASC and was

funded by the Medical Research Council (UK; Grant Code: MR/J500410/1). The work presented in

this manuscript was an attempt to disentangle the cognitive mechanism(s) underlying the previously

observed differences in performance on a visual-tactile task in participants with ASC. Moving

forward, we plan to investigate event related potentials when completing visual-tactile selective

attention tasks to explore whether differences in performance in ASC are reflected in early

perceptual effects or in the resolution of conflict between competing responses.

35

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List of Figures

Figure 1. Schematic of Experiment 1, 2 (A), and Experiment 3 (B) for a right handed participant. In

Experiments 1 and 2, the bone conductor was positioned behind the cardboard shield and appeared

in the same location as the near LED. The far LED was positioned 42cm from the target in the

opposite hemispace. In Experiment 3, the bone conductor was removed and participants were

instructed to keep their dominant hand in a position next to the target light behind the cardboard

shield. In both experiments the near and far distracting LEDs were 27cm from the central fixation

point.

A B

45

Figure 2. Boxplots displaying the congruency effect (CE) in the near and far conditions for

participants with ASC and NT in Experiment 1. The black line represents the median, the hinges are

the upper and lower quartiles and the whiskers extend to the largest/smallest value which is 1.5

times the inter-quartile range from the upper/lower quartile. The CE is calculated as the error rate in

the incongruent condition minus the congruent condition.

46

Figure 3. Percentage error in the congruent (circle) and incongruent (squares) in the near and far

distractor locations in Experiment 1. Error bars denote within participant CI (Couisneau, 2005). The

solid black line gives the error rate in the tactile alone baseline condition and the translucent grey

area gives the boundaries of the CI.

47

Figure 4. Upper panel displays median responses at each SOA for participants with ASC and NT. The

near location is represented by the circles and the solid black line and the far location by the stars

and the dotted line. Error bars denote the upper and lower quartiles. Note that group data is

provided here for illustrative purposes and individual fitted functions were used to calculate the JND

for each group. The lower panel boxplots displays JND (ms) in the near and far locations for

participants with ASC and NT in Experiment 2.

48

Figure 5. The median congruency effect (CE) in the near and far distractor locations for participants

with ASC and NT in Experiment 3. The CE is calculated as the error rate in the incongruent condition

minus the congruent condition.

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Figure 6. Percentage error in the congruent (circle) and incongruent (squares) in the near and far

distractor locations. Error bars denote within participant CI (Couisneau, 2005). The solid black line

gives the error rate in the tactile alone baseline condition and the translucent grey area gives the

boundaries of the within participant CI.

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Figure 7. Boxplots displaying the CE pooled across the near and far distractor locations in Experiment

1 (red) and Experiment 3 (yellow) for participants with ASC and NT. Note that only participants who

were included in the original analysis of both Experiment 1 and Experiment 3 were included here (n=

38).

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