2nd Year PracticalsNovember 2009

Dr Jonathan StirkJAS@psychology.nottingham.ac.uk

Room C44Office Hours: Wednesdays 10-11am

Demonstrator: Daniel AcquahContact by e-mail:

lwxdka@psychology.nottingham.ac.ukRoom: C71

Office hour: Mondays 11-12am

Selective Attention & the Flanker Compatibility Effect (FCE)• Structure of

practical– 5 week structureWeek 1 Mini-lecture, example exp’ts, literature

searchWeek 2 Develop hypothesis, select projectWeek 3 Pilot study, collect dataWeek 4 Data analysis (Mini-lecture)Week 5 PresentationsWeek 6 Hand in written report (Deadline Monday

7th December, 2009 by 4pm.)

Aims of this practical• To learn about the flanker compatibility

effect• To design an experiment to test a specific

hypothesis about flanker effects or using the flanker paradigm

• To learn to implement a design using E-Prime software

• To learn to collect and analyze data using computer software (E-Prime, SPSS)

• To present data in a clear and comprehensible fashion

What is attention?• ‘Attention is the process of

concentrating on specific features of the environment, or on certain thoughts or activities. This focusing on specific features of the environment usually leads to the exclusion of other features of the environment ‘.

Colman (2001)

What is selective attention?• 2 main types of attentional tasks

– Divided attention tasks (dual tasks)• Paying attention equally to more than one

thing– E.g. Reading out loud a story , whilst writing down

dictated words (Spelke, Hurst & Neisser, 1976), driving whilst listening for a specific news item on the radio.

– Selective attention tasks• Paying attention to one source of

information whilst ignoring everything else– E.g. Identifying words presented to the left ear,

whilst ignoring words presented to the right ear in a dichotic listening task (Cherry, 1953)

Models of selective attention• Where within the flow of information

does specific information become selected and other information dismissed? i.e. When does selection take place?

• Does selection occur early in processing or later on?

Sensory Store ResponseSTIMULI

Further processing

Sensory Store ResponseSTIMULI

Further processing

Early versus late models of selective attention• Early-selection models assume that

selection occurs early-on in processing [after analysis of physical characteristics/features e.g. Broadbent (1958)]. From this point on unattended information receives little or no further processing.

• So NO semantic (identification) processing of the ignored/unattended information.

Early versus late models of selective attention• Late-selection models propose that

ALL stimuli are analysed up to the point of identification (to a semantic level) and selection occurs after this point, i.e. later on in the processing stream.

• So to-be-ignored stimuli receive considerable processing and selection occurs much closer to the response end.

Early and late selection

Physical characteristics

Meaning

All messages in

Selected message

Selected message

BIG questions!• Some questions in

attentional research are:

• “To what extent are irrelevant stimuli processed in selective visual attention tasks?”

• “How can we explain what is and isn’t selected?”

How can we examine the extent to which task irrelevant information is processed?• Priming studies

– Do to-be-ignored stimuli prime future performance on a cognitive task?

• Flanker tasks– Do surrounding irrelevant stimuli affect

performance on target stimuli?• Eriksen & Eriksen (1974): classic flanker effect• A response competition paradigm (similar to Stroop!)• This is a selective visual attention task• It can also be used to examine ‘automatic’ processing

of stimuli (processing without attention)• Or… Capture of attention by irrelevant stimuli

Eriksen & Hoffman (1973)• Original exp’t used circular displays

of letters and S’s had to identify the target indicated by a bar cue (out of 4 possible targets) flanked by distracters H

H

AA

H

M

U MU

UM

U

Target sets:

A and U (respond left)

H and M (respond right)

Cue onsets before circle of letters

The flanker compatibility effect• Flankers are stimuli which are presented

spatially close to target stimuli and which should be ignored

• Despite the irrelevance of flankers to the target task they are often shown to interfere with target responses

• The original task involved being presented with 5 letter strings and determining the identity of the middle letter by moving a lever to the left or right

• More modern versions involve left and right hands pressing specific buttons/keys to identify a target

Eriksen et al (1974): linear display task

LEFT HAND RESPONSE

RIGHT HAND RESPONSE

Target:

H K S C

H H K H H

E.g. Respond left

S S C S SE.g. Respond right

flankers flankers

target

REVERSE MAPPINGS CAN BE USED TOO!

Compatibility of responses• However,

the compatibility of the target and flanker responses is important

• RT to target:Incompatible

trials > Compatible trials

Stimuli Compatibility Response hand

Target Flanker

HHKHH Compatible L K H

KKHKK Compatible L H K

SSCSS Compatible R C S

CCSCC Compatible R S C

SSKSS Incompatible L K S

CCKCC Incompatible L K C

CCHCC Incompatible L H C

SSHSS Incompatible L H S

HHCHH Incompatible R C H

KKCKK Incompatible R C K

HHSHH Incompatible R S H

KKSKK Incompatible R S K

Defining the flanker compatibility effect• The FCE is the difference in RT between the two

types of compatibility trials• FCE = Incompatible trials – compatible trials• E.g. 500 ms-420 ms FCE of 80ms

• Sometimes the effect is measured with respect to a base-line condition– One in which flankers are Neutral with respect to target

responses– E.g XXSXX (where the X flanker does not belong to the

target set)– RT differences can then be framed as “costs” or

“benefits”• i.e. we can examine facilitation and interference

What factors moderate the FCE?• Research has shown that the FCE is quite

robust• However, a number of factors have been

shown to moderate the effect• Early research suggested that flanker-

target distance was important– Eriksen & Eriksen (1974) showed that larger

spatial separation (eccentricity) reduced the FCE

– Distracters within 1° of visual angle could not be ignored

– Possible evidence for a ‘fixed-width spotlight’ of selective attention (Posner, 1980)

Fixed-width spotlight metaphor

S C S

< 1 deg

Fixed width (2 deg)

Flankers cannot be ignored as they are within the space selected for attention

Fixed-width spotlight metaphor

S C S

> 1 deg

Fixed width (2 deg)

Flankers may now receive less processing

Explanations of separation effects• The spotlight metaphor helps to explain

the effects of target-flanker separation on the FCE.

• However, other explanations are viable– Visual acuity decreases the further objects are

from the point of fixation• So perhaps increasing the size of flankers/targets is

important in controlling for acuity problems– Distance is confounded by Gestalt grouping

• The law of proximity suggests that closeness effects grouping of stimuli

Law of proximity

Grouped by column Grouped by row

So does perceptual grouping affect the FCE?• What if attention is to objects rather

than space?– If attention is object-based then

principles of grouping may affect what is selected for further processing

– Driver & Baylis (1989) used ‘common motion’ to compete the ‘distance’ vs ‘grouping’ hypotheses

Driver & Baylis (1989)

T TH X H• The results showed that moving distant

distracters (e.g. the H’s above) produced more interference than the static closer distracters (e.g. the T’s above).

• So, perceptual grouping seems important in the allocation of attention and in the FCE

Further effects of grouping• Harms & Bundesen (1983)

– Used colour segregation of targets/distracters

– E.g. (1) F T F versus (2) F T F– This encouraged colour segregation of

targets/distracters in condition 2– Smaller flanker compatibility effects in

condition 2

Further factors moderating FCE• Miller (1991) manipulated five factors to

try and eliminate the FCE and determine any boundary conditions1. Poor spatial resolution2. Inability to hold attentional focus on a fixed

location3. Inability to focus completely on an empty

display location4. Inability to filter out stimuli which onset at the

same time as the target during the task5. Inability to prevent analysis of all stimuli when

there is insufficient demand by the attended items

Consistent & varied mapping• Miller hypothesised that we are unable to

maintain attention on a fixed location and this may be why attention leaks to the irrelevant distracters

• In the linear task the target is always in the same spatial location

• So, he varied the locations of targets/distracters and used a __ (bar) pre-cue to direct attention to the location

• The FCE was NOT diminished when varied mapping was used

+

H

X X

Miller’s Boundary Conditions• Perhaps it is not the constancy but

rather the emptiness of the attended location which prevents early selection from fully excluding other locations from further processing

• Necessary object hypothesis• Miller used an RSVP version of the

flanker task to test this

RSVP task

• The necessary object hypothesis predicts an FCE only when the target appears in frame 1 (as there is no previous object in the target location)

• However, results showed that the FCE was present in later frames refuting the hypothesis

+

F T F F Q F

F * F

F D F F B F

TIME

F = flanker T = target

200ms

200ms

200ms

200ms

12

34

5

Miller’s Boundary Conditions• Maybe we can’t filter out flankers

because they onset at the same time as the target– Yantis & Jonides (1984) had shown that

abrupt onsets attract attention in a visual task

• Miller varied onset/offset transients of flankers/targets

• Used ‘figure 8’ concept.

Yantis & Jonides’ ‘figure 8’

• Results showed that transients had no effect on the FCE

• Transients therefore do not seem to be responsible for the partial leakage of unattended stimuli through an early selection mechanism.

+

Fixation Pre-mask 500ms

Target screen (all offsets in this example

Miller’s Boundary Conditions• What if processing of the irrelevant

flankers is because attentional ‘capacity’ is underloaded leaving room for processing of the flankers?– Perceptual underload hypothesis

• So Miller varied the amount of relevant information and examined the FCE

Perceptual Underload Stimuli

H G J

K D

B C L F F

Flankers

TARGET (attended)REGION

Number of letters varied

Perceptual Underload Stimuli• Results showed that the FCE was

eliminated for the larger set sizes• Finally a boundary condition for FCE?

– NO as there was a confound of timing• Further experiments did NOT support

the underload hypothesis

So what are you going to do?• Get into small groups (3) and design

an experiment to investigate a factor which may effect the FCE

• Design needs to be at least a 2 x 2 factorial design– E.g. 2 IV’s!

• 1. Compatibility of flankers (compatible vs. incompatible)

• 2. Other variable of your own!

Examples of factors to manipulate• Any grouping factor e.g. Colour

segregation– Harms & Bundesen (1983)

• Number of flankers?• Nature of flankers?

– Pictures vs. words?• Target-flanker separation• E.t.c.

So for example… manipulate distanceS,C left H,K right (response pairings)Compatible Incompatible

NearS C S H C H

FarS C S H C H

Leads to 4 conditions (cells) in the design, tested within-subjects

How are you going to do this?• Using E-Prime to control stimulus

display• Create stimuli materials in E-Prime or

maybe using Paint or other graphics program (PowerPoint plus Paint)

• DEMO OF TEMPLATE (using letter stimuli and manipulating target-flanker DISTANCE)

So minimum number of trials is 32Samples need to be weighted to balance out compatible/incompatible trials

What to do - recap• So choose a further IV that you can

manipulate at 2 levels– E.g. you may manipulate a grouping

factor at 2 levels– You might look at what type of

information (e.g. semantic?) can influence target response

• Create stimuli for your experiment• Program E-Prime• Run design

Types of flanker tasks you can use• Classic Letter flanker task S C S• Colour flanker task * * * (Left- red/white, Right- Blue,green)

respond to target colour• Letter-number task 2 A 2 (classify target as either a letter or

a number) • Spatial/Arrows flanker task < < < vs. < > <• Semantic classification flanker task

– Classify names as male/female• E.g. John Samantha John (incompat) vs. June Samantha June (compat)

– Classify target as large/small etc.• Remember this is essentially a response competition

paradigm. If target responses are slowed then it must be because of some flanker processing.

Some References• Bindemann, M., Burton, A., & Jenkins, R. (2005). Capacity limits for face

processing. Cognition, 98(2), 177-197.• Diedrichsen, J., Ivry, R.B., Cohen, A. & Danziger, S. (2000). Asymmetries in

a unilateral flanker task depend on the direction of the response: The role of attentional shift and perceptual grouping. Journal of Experimental Psychology: Human Perception and Performance, 26, 113-126.

• Driver, J. & Baylis, G.C. (1989). Movement and visual attention: the spotlight metaphor breaks down. Journal of Experimental Psychology: Human Perception & Performance, 15(3), 448-456.

• Eriksen, B. A., & Eriksen, C. W. (1974). Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception & Psychophysics, 16, 143-149.

• Eriksen, C.W. (1995). The flankers task and response competition: a useful tool for investigating a variety of cognitive problems. Visual Cognition, 2, 101-118. (available as a .pdf from me)

• Harms, L & Bundesen, C. (1983). Color segregation and selective attention in a nonsearch task. Perception & Psychophysics, 33, 11-19.

Some References• Miller, J. (1991). The flanker compatibility effect as a function of visual

angle, attentional focus, visual transients, and perceptual load: a search for boundary conditions. Perception & Psychophysics, 49 (3), 270-288.

• Shomstein, S. & Yantis, S. (2002). Object-based attention: sensory modulation or priority setting? Perception & Psychophysics, 64(1), 41-51.

• Styles, E. (1997). The psychology of attention. UK: Psychology Press [Chapter 3]

• Jenkins, R., Lavie, N. & Driver, J. (2003). Ignoring famous faces: category-specific dilution of distractor interference. Perception and Psychophysics, 65(2), 298-309.

• Lachter, J., Forster, K. I., & Ruthruff, E. (2004). Forty-five years after Broadbent (1958): Still no identification without attention. Psychological Review, 111(4), 880-913.