Presentation on theme: "2nd Year Practicals November 2008"— Presentation transcript:
1 2nd Year Practicals November 2008 Dr Jonathan StirkRoom C44Office Hours: Wednesdays 10-11amDemonstrator: Maria KtoriContact byRoom: A24Office hour: Mondays 2pm
2 Selective Attention & the Flanker Compatibility Effect (FCE) Structure of practical5 week structureWeek 1Mini-lecture, example exp’ts, literature searchWeek 2Develop hypothesis, select projectWeek 3Pilot study, collect dataWeek 4Data analysis (Mini-lecture)Week 5PresentationsWeek 6Hand in written report (Deadline Monday 8th December, 2008 by 4pm.)
3 Aims of this practical To learn about the flanker compatibility effect To design an experiment to test a specific hypothesis about flanker effectsTo learn to implement a design using E-Prime softwareTo learn to collect and analyze data using computer software (E-Prime, SPSS)
4 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)
5 What is selective attention? 2 main types of attentional tasksDivided attention tasks (dual tasks)Paying attention equally to more than one thingE.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 tasksPaying attention to one source of information whilst ignoring everything elseE.g. Identifying words presented to the left ear, whilst ignoring words presented to the right ear in a dichotic listening task (Cherry, 1953)
6 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 StoreFurther processingResponseSTIMULISensory StoreFurther processingResponseSTIMULI
7 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.
8 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.
9 Early and late selection All messages inPhysical characteristicsMeaningSelected messageSelected message
10 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?”
11 How can we examine the extent to which irrelevant information is processed? Priming studiesDo to-be-ignored stimuli prime future performance on a cognitive task?Flanker tasksDo surrounding irrelevant stimuli affect performance on target stimuli?Eriksen & Eriksen (1974): classic flanker effectA response competition paradigm (similar to Stroop!)This is a selective visual attention taskIt can also be used to examine ‘automatic’ processing of stimuli (processing without attention)Or… Capture of attention by irrelevant stimuli
12 Eriksen & Hoffman (1973)Original exp’t used circular displays of letters and S’s had to identify the presence of a target (out of 4 possible targets) flanked by distractersHUMHUAAMMUUH
13 The flanker compatibility effect Flankers are stimuli which are presented spatially close to target stimuli and which should be ignoredDespite the irrelevance of flankers to the target task they are often shown to interfere with target responsesThe 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 rightMore modern versions involve left and right hands pressing specific buttons/keys to identify a target
14 Eriksen et al (1974): linear display task LEFT HAND RESPONSERIGHT HAND RESPONSEREVERSE MAPPINGS CAN BE USED TOO!Target:HKSCflankersflankersH H K H HE.g.Respond leftS S C S SE.g.Respond righttarget
15 Compatibility of responses However, the compatibility of the target and flanker responses is importantRT to target:Incompatible trials > Compatible trialsStimuliCompatibilityResponse handTargetFlankerHHKHHCompatibleLKHKKHKKSSCSSRCSCCSCCSSKSSIncompatibleCCKCCCCHCCSSHSSHHCHHKKCKKHHSHHKKSKK
16 Defining the flanker compatibility effect The FCE is the difference in RT between the two types of compatibility trialsFCE = Incompatible trials – compatible trialsE.g. 500 ms-420 ms FCE of 80msSometimes the effect is measured with respect to a base-line conditionOne in which flankers are Neutral with respect to target responsesE.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
17 What factors moderate the FCE? Research has shown that the FCE is quite robustHowever, a number of factors have been shown to moderate the effectEarly research suggested that flanker-target distance was importantEriksen & Eriksen (1974) showed that larger spatial separation (eccentricity) reduced the FCEDistracters within 1° of visual angle could not be ignoredPossible evidence for a ‘fixed-width spotlight’ of selective attention (Posner, 1980)
18 Fixed-width spotlight metaphor Flankers cannot be ignored as they are within the space selected for attentionS C S< 1 degFixed width (2 deg)
19 Fixed-width spotlight metaphor Flankers may now receive less processing> 1 degS C SFixed width (2 deg)
20 Explanations of separation effects The spotlight metaphor helps to explain the effects of target-flanker separation on the FCE.However, other explanations are viableVisual acuity decreases the further objects are from the point of fixationSo perhaps increasing the size of flankers/targets is important in controlling for acuity problemsDistance is confounded by Gestalt groupingThe law of proximity suggests that closeness effects grouping of stimuli
21 Law of proximityGrouped by columnGrouped by row
22 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 processingDriver & Baylis (1989) used ‘common motion’ to compete the ‘distance’ vs ‘grouping’ hypotheses
23 Driver & Baylis (1989)HXTTThe 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
24 Further effects of grouping Harms & Bundesen (1983)Used colour segregation of targets/distractersE.g. (1) F T F versus (2) F T FThis encouraged colour segregation of targets/distracters in condition 2Smaller flanker compatibility effects in condition 2
25 Further factors moderating FCE Miller (1991) manipulated five factors to try and eliminate the FCE and determine any boundary conditionsPoor spatial resolutionInability to hold attentional focus on a fixed locationInability to focus completely on an empty display locationInability to filter out stimuli which onset at the same time as the target during the taskInability to prevent analysis of all stimuli when there is insufficient demand by the attended items
26 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 distractersIn the linear task the target is always in the same spatial locationSo, he varied the locations of targets/distracters and used a __ (bar) pre-cue to direct attention to the locationThe FCE was NOT diminished when varied mapping was used
29 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 processingNecessary object hypothesisMiller used an RSVP version of the flanker task to test this
30 RSVP task200msF = flanker T = target200ms5200ms4200ms321The 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
31 Miller’s Boundary Conditions Maybe we can’t filter out flankers because they onset at the same time as the targetYantis & Jonides (1984) had shown that abrupt onsets attract attention in a visual taskMiller varied onset/offset transients of flankers/targetsUsed ‘figure 8’ concept.
32 Yantis & Jonides’ ‘figure 8’ Results showed that transients had no effect on the FCETransients therefore do not seem to be responsible for the partial leakage of unattended stimuli through an early selection mechanism.
33 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 hypothesisSo Miller varied the amount of relevant information and examined the FCE
34 Perceptual Underload Stimuli TARGET (attended)REGIONNumber of letters variedFlankers
35 Perceptual Underload Stimuli Results showed that the FCE was eliminated for the larger set sizesFinally a boundary condition for FCE?NO as there was a confound of timingFurther experiments did NOT support the underload hypothesis
36 So what are you going to do? Get into small groups (3) and design an experiment to investigate a factor which may effect the FCEDesign needs to be at least a 2 x 2 factorial designE.g. 2 IV’s!1. Compatibility of flankers (compatible vs. incompatible)2. Other variable of your own!
37 Examples of factors to manipulate Any grouping factor e.g. Colour segregationHarms & Bundesen (1983)Number of flankers?Nature of flankers?Pictures vs. words?Target-flanker separationE.t.c.
38 So for example… manipulate distance S,C left H,K right (response pairings) CompatibleIncompatibleNearS C SH C HFarS C SH C HLeads to 4 conditions (cells) in the design, tested within-subjects
39 How are you going to do this? Using E-Prime to control stimulus displayCreate 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)
41 So minimum number of trials is 32 Samples need to be weighted to balance out compatible/incompatible trials
42 What to do - recapSo choose a further IV that you can manipulate at 2 levelsE.g. you may manipulate a grouping factor at 2 levelsYou might look at what type of information (e.g. semantic?) can influence target responseCreate stimuli for your experimentProgram E-PrimeRun design
43 Types of flanker tasks you can use Classic Letter flanker task S C SColour flanker task * * * (Left- red/white, Right- Blue,green) respond to target colourLetter-number task 2 A 2 (classify target as either a letter or a number)Spatial/Arrows flanker task < < < vs. < > <Semantic classification flanker taskClassify names as male/femaleE.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.
44 Some ReferencesBindemann, M., Burton, A., & Jenkins, R. (2005). Capacity limits for face processing. Cognition, 98(2),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,Driver, J. & Baylis, G.C. (1989). Movement and visual attention: the spotlight metaphor breaks down. Journal of Experimental Psychology: Human Perception & Performance, 15(3),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,Eriksen, C.W. (1995). The flankers task and response competition: a useful tool for investigating a variety of cognitive problems. Visual Cognition, 2, (available as a .pdf from me)Harms, L & Bundesen, C. (1983). Color segregation and selective attention in a nonsearch task. Perception & Psychophysics, 33,
45 Some ReferencesMiller, 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),Shomstein, S. & Yantis, S. (2002). Object-based attention: sensory modulation or priority setting? Perception & Psychophysics, 64(1),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),Lachter, J., Forster, K. I., & Ruthruff, E. (2004). Forty-five years after Broadbent (1958): Still no identification without attention. Psychological Review, 111(4),