Common Neural Mechanisms for Response Selection and ...

Common Neural Mechanisms for Response Selectionand Perceptual Processing

Yuhong Jiang1 and Nancy Kanwisher12

Abstract

amp Behavioral evidence supports a dissociation betweenresponse selection (RS stimulus-to-response [SndashR] mapping)and perceptual discrimination (PD) The former may besubject to a central processing bottleneck whereas the latteris not (Pashler 1994) We previously (Jiang amp Kanwisher 2003)identified a set of frontal and parietal regions involved in RS asthose that produce a stronger signal when subjects follow adifficult SndashR mapping rule than an easy mapping rule Here wetest whether any of these regions are selectively activated by RSand not perceptual processing as predicted by the centralbottleneck view In Experiment 1 subjects indicated which offour parallel lines was unique in length PD was indexed by a

higher BOLD response when the discrimination was difficultversus easy Stimuli and responses were closely matched acrossconditions We found that all regions-of-interest (ROIs)engaged by RS were also engaged by perceptual processingarguing against the existence of mechanisms exclusivelyinvolved in RS In Experiments 2 and 3 we asked whatprocesses might go on in these ROIs such that they could berecruited by both RS and perceptual processing Our dataargue against an account of this common activation in terms ofspatial processing or general task difficulty Thus PD mayrecruit the same central processes that are engaged by RS amp

INTRODUCTION

Human cognitive abilities are astonishing We rememberevents for decades we acquire knowledge of the worldand of ourselves we recognize faces and objects in aglimpse and we walk and talk and write and sing Yetour cognitive limitations are also striking We can onlykeep track of about four visual objects at a time (Pyly-shyn amp Storm 1988) and we sometimes fail to seeobjects that are right in front of us (Mack amp Rock1998 Levin amp Simons 1997) Over and above ourlimitations in perceptual processing behavioral studieshave shown that we typically cannot compute more thana single stimulus-to-response (SndashR) mapping (or lsquolsquore-sponse selectionrsquorsquo [RS]) at a time (Pashler 1994) Thushuman information processing is limited both at theperceptual level restricting the amount of informationpassing through the perceptual system and at a RS levellimiting what can be acted upon (Allport 1993) In thisstudy we investigate with fMRI the relationship betweenthese two limitations in information processing

Behavioral studies using dual-task paradigms havesuggested that RS may represent a central bottleneckin human information processing (Pashler 1994) Thisbottleneck has two key properties First it is a centrallimitation occurring after perceptual processing but

before motor execution Any two RSs must be carriedout sequentially even when they are based on differentinput and output modalities Thus while we can see ashape and hear a tone at the same time and we canpress a key and say a word at the same time we cannotsimultaneously determine which key to press on thebasis of the shape and determine which word to say onthe basis of the tone Exceptions to this rule are alsoobserved under some conditions (Schumacher et al2001) Second while RS is subject to this lsquolsquocentralprocessing bottleneckrsquorsquo perceptual processing is not(Pashler 1989) Perceptual processing for one task(eg visual search) can often though not always (seeArnell amp Duncan 2002) concur with RS for another(Pashler 1984 1989) In an earlier paper we testedthe first property of RS (modality generality) here wetackle the second property (dissociation from perceptu-al processing)

Jiang and Kanwisher (2003) identified a set of parietaland frontal regions involved in RS that produced ahigher BOLD response in a visualndashmanual task whenthe SndashR mapping rule was complex versus simple (Fig-ure 1) We then showed that these regions were com-monly active during RS for both visual and auditoryinputs and both manual and verbal outputs Thus theseregions behaved in accordance with the modality gen-erality of the RS mechanism found behaviorally

In the present study we tested the second predictionfrom the central processing bottleneck hypothesis

1MIT 2Athinoula A Martinos Center for Biomedical ImagingCharlestown USA

copy 2003 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 158 pp 1095ndash1110

(Pashler 1994) If a central bottleneck affects RS but notperceptual processing (Pashler 1994) then to the ex-tent that functionally distinct processes engage distinctbrain regions (Kinsbourne 1981) at least some of thebrain regions involved in RS should not also be engagedby perceptual processing However if a central bottle-neck affects both RS and perceptual processing (Arnellamp Duncan 2002 DellrsquoAcqua amp Jolicoeur 2000) thenbrain regions involved in the two tasks may be largelysimilar We used a regions-of-interest (ROI) approachfirst functionally identifying brain regions involved in RSin a localizer scan and then asking whether theseregions are engaged by perceptual processing

RESULTS

Behavioral Data Collected During Scanning

Figure 1 shows the task used in Experiment 1 Table 1shows mean RT and accuracy collected during scanningfor all experiments Increased difficulty in perceptualprocessing led to slower RT and poorer accuracy in boththe length discrimination (Experiment 1) and the color-

matching (Experiment 2) tasks There was also a signif-icant drop in performance during the more difficultcondition in the word task (Experiment 3) These dataconfirmed that our manipulation of the difficulty ofthese tasks was successful

Experiment 1 Length Discrimination Task

Whole-Brain Activation Map for Perceptual Processing

In the random effects analysis on the whole brain thecontrast of Fine versus Coarse length discriminationreveals activation in the parietal regions running alongthe intra-parietal sulcus (IPS) extending into the supe-rior parietal lobule (SPL) in the superior frontal regionsnear the frontal eye fields (FEF) bilaterally and in thebilateral dorsal and ventral lateral prefrontal cortex andthe frontal operculuminsula There was also significantactivation in occipitalndashtemporal regions

We also scanned the same subjects in a RS taskinvolving visualndashmanual mapping Two conditionsmdashcompatible and incompatible response mappingmdashweretested We created a statistical map for incompatibleminus compatible mapping To visualize the relation-ship between the two contrasts we overlaid the activa-tion map for visual RS (in red) and perceptualprocessing (in blue) and highlighted the common acti-vations in green (Figure 2) This activation map reveals astriking degree of overlap Activation in the parietalregions was similar for the two contrasts Other over-lapping regions include the FEF the lateral prefrontalcortex and the frontal operculum The stunning degreeof overlap suggests that many brain regions are com-monly engaged in RS and perceptual processing andthus do not show the response profile expected of theRS bottleneck

RS ROI Analysis Do Any Brain Regions Act as RSBottleneck

The ROI analysis permits us to ask in a more focusedfashion and with correspondingly greater statistical pow-er whether any of the regions involved in RS fail to showan activation for perceptual processing as expectedfrom the behavioral literature To address this question

Table 1 Behavioral Performance During Scanning

Accuracy () RT (msec)

Experiment Difficult Easy SE p Difficult Easy SE p

1 Length discrimination 72 97 4 0001 515 349 16 0001

2 Color discrimination 69 98 4 0001 518 404 24 001

3 Word 84 97 3 002 1283 813 30 0001

Localizer scana 94 95 2 ns 561 383 22 0001

aData were taken from Jiang and Kanwisher (2003)

Figure 1 Sample displays (AndashD) and instruction displays (EndashF) usedin the localizer scans and in Experiment 1 The target is the line in aunique length on each display Perceptual discrimination was tested bycontrasting coarse discrimination (A and B) against fine discrimination(C and D) a natural mapping rule (E) was used during instructions inboth conditions RS was tested on displays of coarse discrimination(A and B) only by contrasting natural mapping (E) against unnaturalmapping (F)

1096 Journal of Cognitive Neuroscience Volume 15 Number 8

we measured the percent signal change (PSC) relative tofixation in the fine and coarse length discriminationtasks within the ROIs defined by their RS function Ourlogic is that if any of these ROIs shows a significant effectof perceptual processing that would argue against itsrole as the cortical locus of the RS bottleneck whereas ifan ROI shows no effect of perceptual processing it is acandidate locus of the RS bottleneck

The 13 ROIs were defined based on their activationduring RS as reported in a previous study (Jiang ampKanwisher 2003) these ROIs are anterior and posteriorIPS on the left and the right side (centered on [iexcl36 iexcl5443] [iexcl30 iexcl69 45] [42 iexcl45 45] [30 iexcl66 48]) rightprecuneus ([18 iexcl66 60]) bilateral FEF ([iexcl27 3 48] [33 348]) left inferior prefrontal cortex ([iexcl48 9 21]) bilateralmiddle frontal gyrus ([iexcl45 33 18] [36 44 27]) bilateralfrontal operculuminsula ([iexcl33 24 0] [48 21 iexcl12]) and

right cerebellum ([33 iexcl72 iexcl33]) Table 2 shows the PSCfor each of these ROIs in each perceptual processingcondition of Experiment 1

Twelve of the 13 ROIs showed a highly significantactivation for perceptual processing (fine gt coarselength discrimination) and activation in the other ROI(right cerebellum) was not significant The weakness ofthe cerebellar activation most likely reflects the fact thatnot everyonersquos cerebellum was covered to the samedegree in the slice prescription The magnitude ofactivation in the length discrimination task in all theROIs was comparable to or higher than that for the RStask (Jiang amp Kanwisher 2003) In contrast to thebehavioral evidence that RS relies on a mechanismdistinct from that of perceptual processing our datashowed that all RS ROIs were also involved in percep-tual processing

Figure 2 Overlappingactivation (in green) betweenvisual RS (in red unnaturalmapping gt natural mapping)and perceptual processing(in blue fine discrimination gtcoarse discrimination) in arandom effects analysis(n = 14 p lt 001uncorrected)

Jiang and Kanwisher 1097

The length discrimination task of Experiment 1showed that none of the ROIs satisfied both conditionsof a bottleneck for RS (1) significant activation duringRS and (2) nonsignificant activation during perceptualprocessing These results suggest that in terms of brainregions there is either no localizable central bottleneckor there is a central bottleneck but its function extendsto perceptual processing In the next two experimentswe sought to understand what processes are shared byboth RS and perceptual processing that could explainthe common activation

Experiment 2 Nonspatial Color-Matching Task

Here we tested whether the common activation of ourROIs by both RS and perceptual processing may reflectspatial processing either in the form of finding a targetamong a spatial array of items (Experiment 1) or in theform of spatial remapping In a previous study (Jiangamp Kanwisher 2003) we tested nonspatial RS by havingsubjects make an overt verbal report using either acompatible rule (say lsquolsquosamersquorsquo if two sequential stimulimatched) or an incompatible rule (say lsquolsquodifferentrsquorsquo ifthey matched) The RS ROIs based on incompatiblespatial mapping rules were also activated inthe nonspatial verbal naming task suggesting thatcognitive tasks broader than spatial processing activatethese ROIs

In the current Experiment 2 we provide furtherevidence that the RS ROIs investigated here have abroader function than spatial processing We tested

subjects on a nonspatial perceptual task using sequentialcolor matching Subjects were asked to report whethertwo consecutively presented patches were identical ordifferent in color Discrimination difficulty was increasedby making the two colors more similar on mismatchtrials If the RS ROIs perform specifically spatial functionthey should not be activated in a comparison of difficultversus easy sequential color matching

Whole-Brain Activation Map for Color Matching

Figure 3 shows the regions significantly activated bydifficult versus easy color matching To help visualizethe similarities and differences in activation we alsooverlaid the activation map for the visualndashmanual RStask of Experiment 1 A large amount of commonactivation can be seen (in green) in the bilateral IPSmiddle frontal gyrus frontal operculuminsula and thal-amus In addition the color-matching task activated thefusiform gyrus (see also Beauchamp et al 1999 for arole of this region in color perception) pre-SMA (Rush-worth Hadland Paus amp Sipila 2001) and the anteriorand inferior prefrontal cortex

ROI Analysis Are the RS ROIs Activated by NonspatialPerceptual Discrimination (PD)

To determine whether the RS ROIs are activated bynonspatial PD we measured PSC relative to fixationin each ROI in the easy and difficult color-matchingtask (see Table 3) Among the 13 ROIs that showed RS

Table 2 PSC Relative to Fixation in the Coarse and Fine Length Discrimination Tasks (Experiment 1) in the ROIs Defined by TheirRS Activity

Left Hemisphere ROI Right Hemisphere ROI

PD EasyDifficult RS EasyDifficult PD EasyDifficult RS EasyDifficult

aIPS 015046 011027 010055 000019

pIPS 009036 000020 011057 003023

FEF 021040 017035 015041 013027

GFm iexcl008022 iexcl003009 iexcl003020 iexcl013iexcl006

Operculum 005030 iexcl002008 005045 iexcl009iexcl001 ns

Precuneus NA 000043 000022

GFi 012045 005022 NA

Cerebellum NA 017025 ns 014019 ns

NA = not applicable aIPS = anterior intra-parietal sulcus pIPS = posterior intra-parietal sulcus FEF = frontal eye field GFm = middle frontalgyrus GFi = inferior frontal gyrus PD = perceptual discrimination RS = response selection PSCs were calculated from the raw data afterpreprocessing (motion correction normalization and smoothing)p lt 10

p lt 05

p lt 01

p lt 001


activity 10 showed a significant effect for PD in thecolor task including the anterior and posterior IPSventral and dorsal lateral prefrontal cortex frontal oper-culuminsula and right cerebellum This reinforces theconclusion from Experiment 1 that these ROIs were notselective just for RS Further these ROIs were not justactivated by spatial processing Activation in two otherROIsmdashright FEF and precuneusmdashapproached signifi-cance Finally the left FEF was not sensitive to thediscriminability effect in color matching suggestingthat it may be involved in spatial processing It isunlikely however that the left FEF is involved only inspatial processing because it was significantly activatedby nonspatial RS (Jiang amp Kanwisher 2003) Converselyit is unlikely that the left FEF is insensitive to anynonspatial perceptual processing because it was signif-icantly activated when stimulus contrast was manipu-lated (Schumacher amp DrsquoEspisoto 2000) Further studies

are needed to fully characterize the function of theleft FEF

Experiment 3 Effort of Processing in a Word Task

The first two experiments showed that first all theROIs involved in RS were also significantly involved inperceptual processing and second what drives thiscommon activation is more general than spatial pro-cessing It would be difficult to explain the commonactivation in terms of cognitive control required tomaintain task set (Botvinick Braver Barch Carter ampCohen 2001 Miller amp Cohen 2001 Wagner MarilBjork amp Schacter 2001) because the instructions didnot change between the easy and the difficult condi-tions of perceptual processing yet activation wasdifferent In Experiment 3 we tested the hypothesisthat the common activation across tasks reflect generic

Figure 3 Whole-brainactivation map of thecolor-matching task (in blue)overlaid on the activation mapof the visual RS task (in red)Common regions of activationare shown in green The twocontrasts were generated fromtwo different groups of13 subjects (p lt 005uncorrected random effects)


increases in mental effort If so then the ROIs shouldbe activated by any difficult task

In the word task we presented English words visuallyto our subjects who were required to decide in the easylsquolsquoSyllablersquorsquo task whether the word contained one or morethan one syllables and in the difficult lsquolsquoVerb + Nounrsquorsquotask whether the word could be both verb and noun oreither verb or noun but not both The lsquolsquoVerb + Nounrsquorsquotask was considered more effortful than the lsquolsquoSyllablersquorsquotask by subjective ratings and performance measures(RT and accuracy see Table 1)

Whole-Brain Activation Map in the Word Task

Figure 4 shows the activation map for the difficult wordtask (lsquolsquoVerb + Nounrsquorsquo gt lsquolsquoSyllablesrsquorsquo) in a random effectsanalysis The activation was seen primarily in the lateralprefrontal cortex (ventral and dorsal lateral prefrontalcortex) and the frontal operculuminsula surroundingBrocarsquos area the SMA and pre-SMA with a left-lateralizedpattern In addition activation was also seen in theoccipito-temporal gyrus ([iexcl48 iexcl45 iexcl6]) near regionsthat have been shown to respond to visually presentedwords (Dehaene Le ClecrsquoH Poline Bihan amp Cohen2002 Giraud amp Price 2001) To compare the difficultyeffect in the word task and that in the RS task wegenerated a whole-brain activation map for the visualRS task in the same subjects as the word task and overlaidthe activation maps (see Figure 4) Some regions showedcommon activation for the two difficulty effects in thethalamusbasal ganglia regions and a subset of the leftIPS the left FEF the left inferior prefrontal cortex andthe bilateral frontal operculuminsula

To further visualize whether increased task difficultyhad the same effect in the word task and the visual RStask we created an activation map for the interactionbetween task and difficulty (see Figure 4) Here we findthat the parietal cortex including the anterior andposterior right IPS right precuneus and most anteriorsegment of the left IPS were more sensitive to the RSdifficulty In contrast the left ventral lateral prefrontalcortex and the left operculuminsula were more sensi-tive to difficulty in the word task

ROI Analysis Are the RS ROIs Driven by Generic Effort

Among the ROIs selected because they were activated byRS the right parietal ROIs (right precuneus right ante-rior and posterior IPS) failed to show any differencebetween the difficult word task (Verb + Noun) and theeasy word task (Syllables) This stands in sharp contrastto the robust activation to perceptual processing and RSdescribed earlier Clearly the right parietal regions donot respond to just any difficult task

Table 4 shows the PSC in the word task and the visualRS task in the same group of subjects Because difficultywas manipulated in both tasks we were able to test theTask pound Difficulty interaction effect ANOVAs showed asignificant interaction within all ROIs except the leftFEF The difficulty effect was larger for the word taskthan the RS task in bilateral middle frontal gyrus frontaloperculuminsula left inferior frontal gyrus and rightcerebellum The opposite pattern was seen in the rightparietal ROIs

The significant activation in several RS ROIs to theword task could reflect a role of these regions in

Table 3 PSC Relative to Fixation Within the Visual RS ROIs in the Color-Matching Task (Experiment 2)



aIPS 000015 016028 008029 007023

pIPS iexcl014iexcl003 006022 iexcl006012 009025

FEF 016018 ns 020034 015021 014022

GFm iexcl004011 iexcl003001 ns 004015 iexcl006iexcl003 ns

Operculum 005026 iexcl001002 ns 007043 iexcl003003 ns

Precuneus NA iexcl024iexcl009 006025

GFi 017033 006016 NA

Cerebellum NA 011024 022031

NA = not applicable aIPS = anterior intra-parietal sulcus pIPS = posterior intra-parietal sulcus FEF = frontal eye field GFm = middle frontalgyrus GFi = inferior frontal gyrusp lt 10

p lt 05

p lt 01

p lt 001


processing any difficult task However these activationscould also reflect a more specific role in linguisticprocessing For example the left parietal lateral pre-frontal cortex the frontal operculuminsula and thecerebellum were engaged in syntactic processing andin verbal working memory (Chein amp Fiez 2001 Poldracket al 1999 Jonides et al 1998 Desmond GabrieliWagner Ginier amp Glover 1997 Smith amp Jonides 1997)These issues are discussed further in the Discussion

Additional fMRI Results Across Experiments

Subtle Interaction Effects

So far we have asked whether the regions activated byRS also showed main effects of perceptual processingThe answer is positive Perceptual processing also re-cruits the ROIs defined by their RS activity arguingagainst the hypothesis that these ROIs correspond to

the cognitive central bottleneck In a further analysis weask whether these ROIs are equally sensitive to RS andto perceptual processing To simplify description wewill use the term lsquolsquodifficultyrsquorsquo to describe the differencebetween incompatible and compatible RS mapping andbetween coarse and fine PD We entered data from theROI analysis into an ANOVA with two factors process(RS or PD) and difficulty and we performed this analysison Experiments 1 (length discrimination) and 2 (colordiscrimination) In Experiment 1 we found a significantinteraction between Process and Difficulty in the aIPSpIPS precuneus GFm and operculum At all theseROIs the perceptual processing-related activities werelarger than the RS-related activities This may be ac-counted for by the stronger task manipulation forperceptual processing reflected by the accuracy dataIn Experiment 2 we found significant interaction in theleft FEF the GFm and frontal operculum The left FEFwas highly significant during visual RS but not during

Figure 4 Overlappingactivation (in green) betweenthe visual RS mapping difficulty(in red and pink) and the worddifficulty (in blue and cyan)in 12 subjects (p lt 005uncorrected in a randomeffects analysis) Regions thatshowed significant interactionbetween task (RS vs word) anddifficulty were in pink (greaterdifficulty effect in the visual RStask than the word task) andin cyan (greater difficulty effectin the word than the visualRS task)


color matching but the GFm and frontal operulumshowed the reverse Thus stronger task manipulationfor PD than for RS can explain interaction effects foundin Experiment 1 and the frontal ROIs in Experiment 2The only exception was left FEF which preferred RS tocolor discrimination (but not to length discrimination)As noted earlier because of its sensitivity to manipula-tion of length discriminability and to stimulus contrastthe left FEF is not exclusively devoted to RS In sumalthough the interaction effects suggest that manipula-tions of RS and of PD activate several brain regions todifferent extents they are primarily driven by the greaterstrength of the perceptual processing manipulation thanthe RS manipulation and hence they do not supportthe existence of brain regions devoted to RS

Negative Activation

During effortful cognitive tasks some brain regionstypically show reduced BOLD signal compared with afixation baseline (Raichle et al 2001 Shulman et al1997) Random effects analyses revealed that in thelength discrimination task of Experiment 1 (but notthe color task in Experiment 2) increased perceptualdifficulty led to reduced BOLD in the following regionsthe precuneus ([iexcl3 iexcl66 24]) posterior cingulate([0 iexcl45 36]) middle temporal gyrus ([iexcl48 iexcl63 24][iexcl54 iexcl66 27] [51 3 iexcl30] [54 iexcl63 24] [27 iexcl12 iexcl27])and superior frontal gyrus ([iexcl12 51 25]] [iexcl18 63 18])Some of these regions such as the medial frontal gyrus([iexcl12 51 iexcl3]) middle temporal gyrus ([iexcl54 iexcl12 0])

and posterior cingulate cortex ([12 iexcl54 21]) alsoshowed decreased BOLD as the word task increased indifficulty These were all regions that had previouslybeen noted to show decreased BOLD signal duringcognitive tasks (Gusnard amp Raichle 2001)

Activity in the Anterior Cingulate Cortex (ACC)

The ACC has been postulated to play an important rolein monitoring cognitive conflict (Barch et al 2001 VanVeen Cohen Botvinick Stenger amp Carter 2001 Botvi-nick Nystrom Fissell Carter amp Cohen 1999 CarterBotvinick amp Cohen 1999) In fact Van Veen et alproposed that the ACC monitors response conflict butnot perceptual conflict To test the activity in the ACC in

Table 4 PSC Relative to Fixation Within the Visual RS ROIs in the Localizer Scans and the Word Task (Experiment 3)


Visual RS Word Task Visual RS Word Task

Natural Unnatural Syllable Verb + Noun Natural Unnatural Syllable Verb + Noun

aIPS 010 024 010 043 010 031 iexcl002 002 ns

pIPS 012 028 009 045 012 028 iexcl014 iexcl014 ns

FEF 023 039 014 025 018 035 003 010

GFm iexcl009 003 015 073 iexcl007 iexcl009 ns iexcl008 006

Operculum 004 008 ns 012 045 018 028 ns 012 045

Precuneus NA 014 041 iexcl021 iexcl020 ns

GFi 005 020 030 072 NA

Cerebellum NA 018 028 012 045


p lt 05

p lt 01

p lt 001

Table 5 PSC Relative to Fixation in the ACC AcrossExperiments

Experiment Easy DifficultStandard

Error p Level

Visual RS(localizer)

iexcl010 iexcl005 005 Nonsignificant

1 LengthDiscrimination

iexcl008 018 010 02

2 ColorMatching

iexcl008 021 007 001

3 Word iexcl006 028 005 001


our study here we defined an anatomical ROI centeredon the ACC ([0 33 30] Van Veen et al 2001) It includeda spherical volume of 33 voxels with a radius of 6 mmTable 5 shows the PSC within the ACC in each of theexperiments tested

The ACC was significantly involved in all but the visualRS task On one account the lack of ACC activation inthe visual RS task may be attributed to the blockeddesign which involved constant response conflict withina block with correspondingly reduced necessity forconflict monitoring However the same logic wouldpredict a lack of ACC activation for our other blockeddesign tasks a prediction not borne out by the data Analternative account is that the degree of conflict moni-toring may be smaller in the visual RS task than ourother tasks because it was associated with a smallerperformance decrement Assuming that error rate is agood indicator of the amount of conflict involved in atask the pattern of ACC activation seen in this study isconsistent with the view that the ACC may be importantfor monitoring conflict (Botvinick et al 1999 Carteret al 1999) In any case because the ACC was notinvolved in visual RS the central cognitive bottleneckapparently does not reside here

This conclusion may initially seem inconsistent with astudy reported by Van Veen et al (2001) These authorstested their theory that the ACC is involved in monitor-ing response conflict using the flanker task in which acentral target was flanked by three types of distractors aletter identical to the target a nonidentical letter fromthe same response category or a letter from a differentresponse category Van Veen et al found that the ACCwas engaged in response interference (different re-sponse categorymdashsame category) but not in perceptualinterference (same response categorymdashidentical let-ters) They argued that the ACC may be selectivelyinvolved in monitoring response conflict However intheir study perceptual conflict produced a much smallerbehavioral cost ACC may reflect the degree rather thanthe type of conflict In a median RT split analysis VanVeen et al failed to find ACC activation for slow or fast

trials for perceptual conflict However a median RT splitanalysis on response conflict showed no effect of RT onACC either supporting the idea that RT variance withina condition is better accounted for by random variationthan degree of conflict Thus Van Veen et alrsquos studydoes not provide strong evidence that response inter-ference alone uniquely activates the ACC and hence itdoes not contradict the conclusions that we reach here

Activation in the Thalamus

The thalamus has been implicated as a possible locus ofthe central RS bottleneck In a study on split-brainpatients Pashler et al (1994) found that when two RSswere made one with the left and the other with theright hemisphere a severe dual-task interference wasstill observed in these patients They proposed that theinterference must have arisen from crosstalk in subcor-tical regions perhaps in the thalamus To find outwhether thalamus is selectively involved in RS herewe defined two functional ROIs centered on the mostsignificant voxels (incompatiblendashcompatible RS) in theleft and the right thalamus ([iexcl18 iexcl21 9] and [18 21 12])A spherical volume with a radius of 6 mm was definedsurrounding the center of each ROI Table 6 shows thePSC within the thalamus in all the tasks

The left thalamus was significantly activated only inthe word task whereas the right thalamus was signifi-cantly activated in the length discrimination and theword task In neither ROIs was the activation selectivefor visual RS Thus the thalamus does not correspond tothe central processing bottleneck although it may servean important role in some cognitive processing (HuettelGuzeldere amp McCarthy 2001 Monchi Petrides PetreWorsley amp Dagher 2001)

Laterality Effects

So far we have tested the 13 ROIs as regions unrelatedto one another yet it is well known that homologousregions in the two hemispheres often have similar but

Table 6 PSC Relative to Fixation in the Thalamus across Experiments

ROI Experiment Easy Difficult SE p Level

Left thalamus [iexcl18 iexcl21 9] Visual SR (localizer) 000 001 003 ns

1 Length discrimination 003 005 004 ns

2 Color matching iexcl005 iexcl001 002 ns

3 Word 001 009 003 017

Right thalamus [18 21 12] Visual SR (localizer) 003 005 004 ns

1 Length discrimination iexcl004 007 004 008


3 Word iexcl008 005 005 029


nonidentical functions To find any subtle functionaldifferences between the left and the right ROIs herewe tested the laterality effects in the five sets of bilateralROIs The visual RS task (localizer scan) producedlargely symmetric activation in the two hemispheresHowever the length discrimination task of Experiment 1produced a right-lateralized pattern showing significantinteraction between hemisphere and perceptual pro-cessing in all the ROIs The effect of perceptual discrim-inability was significant on both left and right ROIs butmore so on the right The right-lateralized perceptualprocessing effect is consistent with the observation thatthe right parietal regions are more important than theirleft counterparts in visual attention (Driver amp Mattingly1998 Driver amp Vuilleumier 2001 Rafal 1994) The right-lateralized effects may be related to orienting perceptualprocessing in space because except for the frontaloperculuminsular regions the other ROIs did not showa right-lateralized pattern in the nonspatial color-match-ing task Finally the word difficulty task showed a left-lateralized pattern in the parietal cortex the middlefrontal gyrus and the FEF consistent with the generallyaccepted view that the left hemisphere may have adominant role in language processing

Unique Activation for Perceptual Processing

Although our ROI analysis addressed the question aboutwhether there was a RS central bottleneck by limitinganalysis to RS regions it does not answer whether thereare any regions activated by perceptual processing butnot RS To find out we performed a mapwise interactiontest between difficulty and process (RS vs perception) inExperiments 1 and 2 Across the length discriminationand the color-matching tasks we observed at least tworegions that showed unique perceptual effects (see Table7) One lies in the occipitalndashtemporal cortex Its activa-tion may be accounted for by increased attention tovisual pattern or color as the PD became more difficult

Another region lies in the anterior and ventral lateralprefrontal cortex Such anterior activation is surprisingfor several reasons First it does not fit naturally withthe view that the posterior attention network mediatesvisuospatial attention while the anterior attention net-work mediates response conflict and executive control(Casey et al 2000 Posner amp Petersen 1990) Second itdoes not fit with the characterization of the ventrallateral prefrontal as responsible for cognitive control oftask set (Botvinick et al 2001 De Fockert et al 2001Miller amp Cohen 2001 Wagner et al 2001) becausemanipulation of PD does not alter the amount ofcognitive control any more than the SndashR incompatibilitydoes Whether the activation here was driven by theerror trials only or by the greater generic difficulty ofthe perceptual task awaits further tests using event-related designs

DISCUSSION

In this study we asked whether any brain regions thatare engaged in RS but not in perceptual processing aspredicted by the behavioral literature on the centralprocessing bottleneck (Pashler 1994) exist In contrastto this prediction we found in Experiment 1 that all ofthe ROIs that were engaged in RS were also activated bya perceptual length discrimination task Our study thusposes a challenge to the notion of a cognitive bottle-neck the fMRI data or both

On the one hand there may in fact be neuralpopulations corresponding to the RS bottleneck thatour fMRI data have failed to reveal First RS may rely onneural populations that are distinct from those involvedin perceptual processing but that are so closely inter-mingled that they cannot be resolved with fMRI Secondeven if RS is carried out by the same neural populationas perceptual processing it may nonetheless be func-tionally dissociable from perceptual processing Thismay be accomplished by separating the two functions

Table 7 PSC Relative to Fixation in Regions that Were Significantly Activated during Perceptual Processing but not RS

Experiment Coordinate Location EasyDifficult RS EasyDifficult PD

1 Length [27 iexcl78 30] Occipital gyrus (area 19) iexcl013iexcl012 ns iexcl006008

[iexcl42 iexcl72 iexcl12] Fusiform gyrus iexcl004001 008022

[44 33 9] GFi (area 46) iexcl015iexcl010 ns iexcl016018

2 Color [39 iexcl66 iexcl9] Occipital temporal G iexcl003iexcl002 ns 004014

[iexcl39 21 iexcl12] GFi (area 47) iexcl001003 ns 0024

[36 27 iexcl9] GFi (area 47) iexcl006iexcl003 ns 007040

RS visualndashmanual response selection PD = perceptual discrimination

p lt 05

p lt 01

p lt 001


into distinct temporal stages or phases of processingwithin the same neural population (Singer 1993) Test-ing these (and other) accounts will require the use ofother techniques beyond fMRI

On the other hand the central bottleneck may notonly be selective for RS but it may also be engaged indifficult PD In fact recent behavioral studies havesuggested that memory retrieval short-term memoryconsolidation change detection of visual patterns men-tal imagery and other forms of image manipulation mayalso tie up the central processing bottleneck (eg Arnellamp Duncan 2002 DellrsquoAcqua amp Jolicoeur 2000) Our fMRIdata are consistent with these studies by showing thatfronto-FEFndashparietal regions may have a role more gen-eral than RS but more specific than generic difficulty

An important task for future behavioral as well asneuroimaging studies is to enumerate the tasks thatengage the central bottleneck It is important to notehowever that as the list gets longer the notion of astructural bottleneck loses some of its attraction In-deed some researchers argue that there may not be acentral bottleneck after all and the reported dual-taskinterference may be attributed to a strategic ratherthan a structural cognitive bottleneck On this viewsubjects may flexibly adjust its locus (and existence)depending on task priority practice or SndashR compati-bility (Meyer amp Kieras 1997 Schumacher et al 2001)Thus another interpretation of our fMRI data is thatRS and perceptual processing do not rely on distinctfunctions after all On this interpretation the remain-ing challenge will be to characterize the actual pro-cesses that occur in common during both RS andperceptual processing

Effects of Spatial Processing and Task Difficulty

The patterns of activation that we found for RS and forperceptual processing were strikingly similar (Figure 2)Experiments 2 and 3 asked what might be going on inthe cortical regions that are activated during both tasks(ie the IPS FEF GFiGFm and frontal operculuminsula) Their function is apparently more general thanspatial processing alone because most of these regionsshow unambiguous activation in nonspatial tasks Forexample these ROIs were all involved in a nonspatial RStask when subjects verbally reversed the response (egsay lsquolsquodifferentrsquorsquo when successive colors matched in colorJiang amp Kanwisher 2003) In addition with the possibleexception of the left FEF the ROIs were also implicatedin a nonspatial color-matching task when PD wasmade more difficult (Experiment 2 here) Even the leftFEF may be involved in some nonspatial perceptualprocessing because its activity has been shown toincrease as stimulus contrast decreases (Schumacher ampDrsquoEspisoto 2000) Thus although some regions such asthe SPL precuneus and FEF may be preferentiallyengaged in spatial processing (Berman et al 1999

Labar et al 1999 Culham et al 1998) all the ROIsinvestigated here apparently play an important role inboth spatial and nonspatial attention (Wojciulik ampKanwisher 1999)

However the function of the RS regions is lessgeneral than generic mental effort An account of ourROI activations based on general task difficulty wouldpredict that these regions are activated by any difficulttask However the complete lack of activation in theright parietal cortex when the word task increased indifficulty (Experiment 3) argues against this accountLess clear is the interpretation of the other regionsthat showed a significant Task (visual RS vs wordtask) pound Difficulty interaction but that were also sig-nificant in both tasks If these regions responded onlyas a function of generic difficulty then all regionsshould show the same activation profiles which inturn should reflect the task difficulty measured behav-iorally (eg the 470-msec RT cost in the word taskmight be expected to lead to stronger activations thanthe 166-msec cost in the RS task) However ourresults show that some regions were more stronglyactivated by the word task (eg the left operculuminsula) while others were more strongly activated byRS (eg the right FEF) This double dissociationcannot be easily handled by a simple account basedon generic effort

Thus the function of these fronto-FEFndashparietal ROIsis apparently more general than spatial processing andis more specific than generic effort Although anunderstanding of the precise functions of these re-gions must await future research they may include RSworking memory LTM encoding and retrieval andexecutive control (Culham amp Kanwisher 2001 Duncanamp Owen 2000) The necessity to exert cognitivecontrol may be a common theme across many ofthese tasks (De Fockert et al 2001 Miller amp Cohen2001 Wagner et al 2001) However as argued earliercognitive control in the sense of maintaining task setis unlikely to be strongly affected by the perceptualdiscriminability manipulation used in Experiments 1and 2 An important task for future studies is todetermine the essential process(es) that activate thesebrain regions

Generalization of the Findings

Both RS and perceptual processing may be operational-ized in various ways Do our results generalize to otherparadigms for testing RS and perceptual processing Theregions that we identified here for RS are based on acompanion study that found the same regions to beactivated in manipulations of SndashR compatibility usingboth visual and auditory input modalities and bothspatial and nonspatial mapping paradigms (Jiang ampKanwisher 2003) Other studies that manipulate RSusing the Stroop task the flanker task the antisaccade


task and other response competition tasks have activat-ed regions similar to those that we identified here(Banich et al 2000 Connolly Goodale Desouza Me-non amp Vilis 2000 Hazeltine Poldrack amp Gabrieli 2000Leung Skudlarski Gatenby Peterson amp Gore 2000Botvinick et al 1999 Carter et al 1999 Bush et al1998 Pardo Pardo Janer amp Raichle 1990) Paradigmsfor testing perceptual processing have varied even morewidely (Pashler 1998) Many neuroimaging studies havedemonstrated that the frontal-FEFndashparietal network isinvolved in allocating attention to space (Corbetta ampShulman 2002 Culham amp Kanwisher 2001) one of themost commonly tested forms of perceptual attentionHere we have extended these findings to show thateven nonspatial attention can also activate the samenetwork (see also Coull Frith Buchel amp Nobre 2000Marois Chun amp Gore 2000 Wojciulik amp Kanwisher1999) Thus our finding of activation in the fronto-FEFndashparietal regions for perceptual processing and RSapparently generalizes to other paradigms for testingthese functions

Relation to Prior Studies

Although many studies have investigated RS or per-ceptual processing alone only a few have testedwhether RS selectively activates brain regions notengaged by perceptual processing In two relevantstudies Marois Larson Chun and Shima (2002) andSchumacher and DrsquoEspisoto (2000) orthogonally variedperceptual difficulty (via stimulus contrast) and RSdifficulty (via SndashR compatibility or the number ofresponse alternatives) Many of the findings of thesestudies are consistent with those that we report hereHowever in important contrast to our findings bothstudies reported some regions activated by RS but notperceptual processing The failure of these studies tofind an increased activation for perceptual processingin these regions may result from a lack of statistical orexperimental power Consistent with this interpreta-tion Schumacher and DrsquoEsposito reported activationsfor perceptual processing in the premotor cortex notfound by Marois et al and Marois et al reportedperceptual activations in the parietal cortex not foundby Schumacher and DrsquoEsposito Further other studieshave reported activations from spatial attention inregions these studies found to be selective for RS(Cabeza amp Nyberg 2000 Culham amp Kanwisher2001) Note that even if only some not all perceptualprocessing manipulations activate each region implicat-ed in RS that is sufficient to undermine the claim thatthese regions are selective for RS Thus although wedo not yet have a complete account of the discrep-ancies between our findings and those of Marois et al(2002) and Schumacher and DrsquoEspisoto (2000) thesestudies do not provide evidence against our claim thatbrain regions involved in RS are also involved in

perceptual processing Our data thus challenge thenotion of a localizable RS bottleneck

METHODS

Subjects

Twenty-eight subjects between the age of 18 and 43(Mean = 232 SD = 52) participated in these studies(13 women and 15 men) Fourteen subjects were testedin Experiment 1 13 in Experiment 2 12 in Experiment 3and 17 in the localizer scans Some subjects werescanned in multiple experiments

Testing Procedure

Subjects received 5 min of practice in each task on thesame day or the day before the scan They were scannedon a Siemens 30 T head-only scanner All scanning tookplace at the Athinoula A Martinos Center for BiomedicalImaging in Charlestown MA The scanning procedureand parameters were similar to the one used in thecompanion paper (Jiang amp Kanwisher 2003) Twentyoblique axial slices 6 mm thick with 0 mm distancebetween slices were scanned We used a T2-weightedEPI sequence (TR = 2000 msec TE = 20 msec flipangle = 908 resolution = 313 pound 313 pound 600 mm) forthe functional scans For the localizer scan and Experi-ments 1 (length discrimination) and 2 (color matching)each scan lasted 6 min 4 sec For Experiment 3 (wordtask) each scan lasted 5 min 44 sec The first 8 sec ofeach scan was discarded

Scan Composition

Each functional scan used a blocked design with threeconditions fixation (F) task A and task B The compar-ison between tasks A and B is our main contrast ofinterest In all experiments the two tasks were matchedin low-level visual input and in motor output Differ-ences between tasks were introduced by instructions(Experiment 3 and the localizer scans) or by stimulussimilarity within a trial (Experiments 1 and 2) In thelocalizer scan and the first two experiments the scanwas composed of a series of blocks in which task wascounterbalanced in order (ABABBABA or ABBABAAB)and fixation blocks preceded each task and followedthe last task Each task block lasted 64 sec and eachfixation was 20 sec The first four fixation blockswere each composed of a 15-sec fixation followed by a5-sec instruction

In the word task (Experiment 3) the scan was alsocomposed of fixation and two tasks in a similar struc-ture as in the other experiments Each task block lasted60 sec and the first four fixation blocks each lasted20 sec composed of a 16-sec fixation followed by a 4-secinstruction The last fixation block was 16 sec


Materials and Tasks

Stimuli were presented using the Psychtoolbox imple-mented in MATLAB (Brainard 1997)

Experiment 1 Length Discrimination

Each trial (2 sec) of the length discrimination task startedwith a visual display of 100 msec followed by a 100-msecmask and then a 1800-msec fixation display Each displaycontained four vertical lines three of which were iden-tical and the other was unique in length either shorter orlonger The lines were chosen from four possiblelengths 318 288 108 or 088 The four lines wereevenly spaced on a 6258 pound 6258 display (Figure 1AndashD)The mask was made of 18 vertical and 18 horizontal lines(length = 6258) semiirregularly displaced

The task was to identify the line with a unique lengthin each display and report its spatial position among thefour lines by pressing one of four keys Subjects com-fortably rested their index middle ring and little fingersof the right hand on keys 1 2 3 and 4 The targetposition was mapped onto the keys according to acompatible mapping rule for every block (Figure 1E)so the instructions preceding each block were the sameTasks A (coarse discrimination) and B (fine discrimina-tion) differed in how the lines were paired on a trial Inthe coarse discrimination task the shorter line(s) waseither 108 or 088 and the longer line(s) was either 318or 288 In the fine discrimination task the two shortestlines (108 and 088) were paired on a trial and the twolonger lines (318 and 288) were paired on a trial Eachsubject performed two scans

The Localizer Scan Visual RS

The localizer scans were similar in procedure to thelength discrimination task This task has been describedpreviously (Jiang amp Kanwisher 2003) Stimuli tested inthis task were the same as those in the coarse discrim-ination of Experiment 1 in which the target length wasobviously different from the distractors What differedbetween tasks was the instructions preceding eachblock The SndashR mapping rule between the target posi-tion and the key position was either compatible (Figure1E) or incompatible (Figure 1F)

Experiment 2 Color Matching

On each trial two color patches (diameter = 0938)were presented at fixation each was presented for 100msec and a 100-msec blank interval intervened be-tween them Subjects were asked to judge whether thecolors were identical or different The colors werechosen from two shades of green (RGB values [0 2550] and [0 175 0]) and two shades of blue (RGB values[0 0 255] and [0 0 170]) The background was black

Half of the trials were match trials the other half weremismatch trials In the easy color-matching conditionwhen colors mismatched one was chosen from one ofthe green colors and the other was chosen from oneof the blue colors In the difficult color-matchingcondition when colors mismatched the two colorswere two shades of green or two shades of blue Ineach task block each color was presented the samenumber of time in the easy and difficult color match-ing but the pairing within a trial differed

Subjects were instructed to push the left key withtheir right index finger if the colors matched and theright key using their right middle finger if they mis-matched The instructions preceding each block in-formed subjects whether the difference on mismatchtrials would be small or large so subjects could adopt anappropriate criterion to differentiate mismatch frommatch trials Each subject performed two or four scans

Experiment 3 Word Task

Ten different lists of 24 words (4ndash7 letters) were createdEach list contained equal number of one-syllable words(eg lsquolsquoflightrsquorsquo lsquolsquopausersquorsquo) and multisyllable words (eglsquolsquolocatersquorsquo lsquolsquocopyrsquorsquo) Further one- or multisyllable wordscontained equal number of one- or multicategory wordsMulticategory words were both a verb and a noun (eglsquolsquopausersquorsquo lsquolsquocopyrsquorsquo) while one-category words were eithera verb (eg lsquolsquolocatersquorsquo) or a noun (eg lsquolsquoflightrsquorsquo) but notboth (half of these were verb only and half were nounonly) In the lsquolsquoSyllablersquorsquo task subjects pushed the left keyfor one-syllable words and the right key for multisyllablewords In the lsquolsquoVerb + Nounrsquorsquo task subjects pushed theleft key for one-category words and the right key formulticategory words

In the 60 sec of each block there were 24 trials eachlasting 25 sec The word was presented at fixation for200 msec (in helvetical font point size 72) followed by afixation period of 23 sec The same word was judgedtwice once in the Syllable task and once in the Verb +Noun task Each scan (eg in either ABBA or BAABorder) tested two different lists one list for the first twoblocks and the other for the last two blocks The blockorder ensured that half of the lists were tested in theSyllable task first and the other half in the Verb + Nountask first All subjects practiced on two lists and werescanned on the other eight (or four) lists Each subjectperformed two or four scans

fMRI Data Analysis Logic

Two different kinds of analyses were conducted on thedata from each experiment First we created a whole-brain statistical map using a random effects analysis forthe effect of interest (eg perceptual processing in thelength task) The activation map was then overlaid on anactivation map from the RS task from the localizer scans


so as to visualize the similarities and differences inactivation between different contrasts

Second to test the specific question of our studymdashwhich brain regions underlie the RS bottleneckmdashwerelied on the ROIs approach Here we defined ROIsbased on their RS activity in a previous study (Jiang ampKanwisher 2003) and calculated the PSC from fixationfor perceptual processing A significant perceptual pro-cessing effect in a particular ROI indicates that this ROI issensitive to perceptual processing and therefore doesnot satisfy the criterion of a RS bottleneck In contrastan ROI that does not show an effect of perceptualprocessing would be a candidate region for the RSbottleneck

fMRI Data Analysis Procedure

Activation Map

Data were analyzed using SPM99 (httpwwwfilionuclacukspmspm99html) After preprocessing (seeJiang amp Kanwisher 2003) we analyzed each subjectrsquosdata for the contrast of interest and conducted a randomeffects analysis ( p lt 001 uncorrected for the localizerscan and Experiment 1 and p lt 005 uncorrected forExperiments 2 and 3)

We localized RS ROIs in a previous study (Jiang ampKanwisher 2003) There we split the four scans of thevisual RS task into two sets of two scans each One dataset was used in the random effects group analysis whichfunctionally defined ROIs (incompatible gt compatiblemapping) at the group level Each group ROI containedvoxels that are significant at p lt 001 level uncorrectedfor multiple comparisons and was centered on the localmaximal Each group ROI was within a spherical volumecontaining the significant voxels the radius of the ROIswas between 6 and 12 mm with the constraint thatdifferent ROIs did not overlap Once these ROIs weredefined we measured the PSC within these ROIs in theother half of the data and confirmed that these ROIswere involved in RS

In the current study we selected the same ROIs asdefined by the previous study Most subjects in Exper-iment 1 (N = 13) and all subjects in Experiment 3 weretested in those localizer scans allowing us to adjust thefunctional ROIs according to individual subjectsrsquo local-izer activation For these subjects we adjusted the ROIsby taking only the voxels that fell within the group ROIsthat were also active in that individual subjectrsquos localizerscans The individually adjusted ROIs allowed anatomicalvariation across subjects to be expressed while ensuringthat the voxels were still representative of the generalpopulation For other subjects the individual ROIs werethe same as the group ROIs

PSC relative to the fixation baseline was calculated foreach task of interest (eg coarse and fine length dis-crimination) within each ROI for each subject We then

tested whether there was a significant effect of (say)perceptual processing within each ROI A lack of activa-tion for perceptual processing within the RS ROIs wouldmean that ROI was a candidate brain region for theRS bottleneck

Acknowledgments

This work was supported by a Human Frontiersrsquo grant to NKYJ was supported by a research fellowship from the Helen HayWhitney Foundation We thank Miles Shuman for the technicalassistance Kyungmouk Lee for the data analysis and DavidBadre John Duncan Mark DrsquoEsposito Molly Potter RebeccaSaxe and Eric Schumacher for the helpful comments

Reprint requests should be sent to Yuhong Jiang currently atthe Department of Psychology Harvard University 33 KirklandSt Room 820 Cambridge MA 02138 USA or via e-mailyuhongwjhharvardedu

The data reported in this experiment have been deposited inThe fMRI Data Center (httpwwwfmridcorg) The accessionnumber is 2-2003-113RG

REFERENCES

Allport A (1993) Attention and control Have we been askingthe wrong questions A critical review of twenty-five yearsIn D E Meyer amp S Kornblum (Eds) Attention andperformance 14 Synergies in experimental psychologyartificial intelligence and cognitive neuroscience(pp 183ndash218) Cambridge MIT Press

Arnell K M amp Duncan J (2002) Separate and shared sourcesof dual-task cost in stimulus identification and responseselection Cognitive Psychology 44 105ndash147

Banich M T Milham M P Atchley R Cohen N J Webb AWszalek T Kramer A F Liang Z-P Wright A ShenkerJ amp Magin R (2000) fMRI studies of Stroop tasks revealunique roles of anterior and posterior brain systems inattentional selection Journal of Cognitive Neuroscience12 988ndash1000

Barch D M Braver T S Akbudak E Conturo T OllingerJ amp Snyder A (2001) Anterior cingulate cortex andresponse conflict Effects of response modality andprocessing domain Cerebral Cortex 11 837ndash848

Beauchamp M S Haxby J V Jennings J E amp De Yoe E A(1999) An fMRI version of the Fansworth-Munsell 100-Huetest reveals multiple color-selective areas in human ventraloccipitotemporal cortex Cerebral Cortex 9 257ndash263

Berman R A Colby C L Genovese C R Voyvodic J TLuna B Thulborn K R amp Sweeney J A (1999) Corticalnetworks subserving pursuit and saccadic eye movements inhumans An fMRI study Human Brain Mapping 8209ndash225

Botvinick M Nystrom L E Fissell K Carter C S amp CohenJ D (1999) Conflict monitoring versus selection-for-actionin anterior cingulate cortex Nature 402 179ndash181

Botvinick M M Braver T S Barch D M Carter C S ampCohen J D (2001) Conflict monitoring and cognitivecontrol Psychological Review 108 624ndash52

Brainard D H (1997) The psychophysics toolbox SpatialVision 10 433ndash436

Bush G Whalen P J Rosen B R Jenike M A McInerneyS C amp Rauch S L (1998) The counting Stroop Aninterference task specialized for functional neuroimagingmdashvalidation study with functional MRI Human BrainMapping 6 270ndash282


Cabeza R amp Nyberg L (2000) Imaging Cognition II Anempirical review of 275 PET and fMRI studies Journal ofCognitive Neuroscience 12 1ndash47

Carter C S Botvinick M M amp Cohen J D (1999) Thecontribution of the anterior cingulate cortex to executiveprocesses in cognition Reviews in the Neurosciences 1049ndash57

Casey B J Thomas K M Welsh T F Badgaiyan R EccardC H Jennings J R amp Crone E A (2000) Dissociation ofresponse conflict attentional control and expectancy withfunctional magnetic resonance imaging (fMRI) Proceedingsof the National Academy of Sciences USA 97 8728ndash8733

Chein J M amp Fiez J A (2001) Dissociation of verbal workingmemory system components using a delayed serial recalltask Cerebral Cortex 11 1003ndash1014

Connolly J D Goodale M A Desouza J F Menon R S ampVilis T (2000) A comparison of frontoparietal fMRIactivation during anti-saccades and anti-pointing Journal ofNeurophysiology 84 1645ndash1655

Corbetta M amp Shulman G L (2002) Control of goal-directedand stimulus-driven attention in the brain Nature ReviewsNeuroscience 3 201ndash215

Coull J T Frith C D Buchel C amp Nobre A C (2000)Orienting attention in time Behavioral and neuroanatomicaldistinction between exogenous and endogenous shiftsNeuropsychologia 38 808ndash819

Culham J C Brandt S A Cavanagh P Kanwisher N GDale A M amp Tootell R B H (1998) Cortical fMRIactivation produced by attentive tracking of moving targetsJournal of Neurophysiology 80 2657ndash2670

Culham J C amp Kanwisher N G (2001) Neuroimaging ofcognitive functions in human parietal cortex CurrentOpinion in Neurobiology 11 157ndash163

De Fockert J W Rees G Frith C D amp Lavie N (2001) Therole of working memory in visual selective attentionScience 291 1803ndash1806

Dehaene S Le ClecrsquoH G Poline J B Le Bihan D amp CohenL (2002) The visual word form area A prelexicalrepresentation of visual words in the fusiform gyrusNeuroReport 13 321ndash325

DellrsquoAcqua R amp Jolicoeur P (2000) Visual encoding ofpatterns is subject to dual-task interference Memory ampCognition 28 184ndash191

Desmond J E Gabrieli J D Wagner A D Ginier B L ampGlover G H (1997) Lobular patterns of cerebellaractivation in verbal working-memory and finger-tappingtasks as revealed by functional MRI Journal ofNeuroscience 17 9675ndash9685

Driver J amp Mattingley J B (1998) Parietal neglect and visualawareness Nature Neuroscience 1 17ndash22

Driver J amp Vuilleumier P (2001) Perceptual awareness andits loss in unilateral neglect and extinction Cognition 7939ndash88

Duncan J amp Owen A M (2000) Common regions of thehuman frontal lobe recruited by diverse cognitive demandsTrends in Neurosciences 23 475ndash483

Giraud A L amp Price C J (2001) The constraints functionalneuroimaging places on classical models of auditory wordprocessing Journal of Cognitive Neuroscience 13754ndash765

Gusnard D A amp Raichle M E (2001) Searching for abaseline Functional imaging and the resting human brainNature Reviews Neuroscience 2 685ndash694

Hazeltine E Poldrack R amp Gabrieli J D (2000) Neuralactivation during response competition Journal ofCognitive Neuroscience 12 118ndash129

Huettel S A Guzeldere G amp McCarthy G (2001)Dissociating the neural mechanisms of visual attention in

change detection using functional MRI Journal of CognitiveNeuroscience 13 1006ndash1018

Jiang Y amp Kanwisher N (2003) Common neuralsubstrates for response selection across modalities andmapping paradigms Journal of Cognitive Neuroscience 151080ndash1094

Jonides J Schumacher E H Smith E E Koeppe R A AwhE Reuter-Lorenz P A Marshuetz C amp Willis C R (1998)The role of parietal cortex in verbal working memoryJournal of Neuroscience 18 5026ndash5034

Kinsbourne M (1981) Single channel theory In D Holding(Ed) Human skills (pp 65ndash89) Chichester England Wiley

LaBar K S Gitelman D R Parrish T B amp Mesulam M M(1999) Neuroanatomic overlap of working memory andspatial attention networks A functional MRI comparisonwithin subjects Neuroimage 10 695ndash704

Leung H C Skudlarski P Gatenby J C Peterson B S ampGore J C (2000) An event-related functional MRI study ofthe Stroop color word interference task Cerebral Cortex10 552ndash560

Levin D T amp Simons D J (1997) Failure to detect changesto attended objects in motion pictures PsychonomicBulletin amp Review 4 501ndash506

Mack A amp Rock I (1998) Inattentional blindnessCambridge MIT Press

Marois R Chun M M amp Gore J C (2000) Neural correlatesof the attentional blink Neuron 28 299ndash308

Marois R Larson J M Chun M M amp Shima D (2002)Neural correlates of the response bottleneck Posterpresented at the 20th Meeting of Attention andPerformance

Meyer D E amp Kieras D E (1997) A computational theory ofexecutive cognitive processes and multiple-taskperformance Part 2 Accounts of psychological refractory-period phenomena Psychological Review 104 749ndash791

Miller E K amp Cohen J D (2001) An integrative theory ofprefrontal cortex function Annual Review of Neuroscience24 167ndash202

Monchi O Petrides M Petre V Worsley K amp Dagher A(2001) Wisconsin Card Sorting revisited Distinct neuralcircuits participating in different stages of the task identifiedby event-related functional magnetic resonance imagingJournal of Neuroscience 21 7733ndash7741

Pardo J V Pardo P J Janer K W amp Raichle M E (1990)The anterior cingulate cortex mediates processing selectionin the Stroop attentional conflict paradigm Proceedings ofthe National Academy of Sciences USA 87 256ndash259

Pashler H (1984) Processing stages in overlapping tasksEvidence for a central bottleneck Journal of ExperimentalPsychology Human Perception amp Performance 10358ndash377

Pashler H (1989) Dissociations and dependencies betweenspeed and accuracy Evidence for a two-component theoryof divided attention in simple tasks Cognitive Psychology21 469ndash514

Pashler H (1994) Dual-task interference in simple tasks Dataand theory Psychological Bulletin 116 220ndash244

Pashler H (1998) The psychology of attention CambridgeMIT Press

Pashler H Luck S J Hillyard S A Mangun G R OrsquoBrienS amp Gazzaniga M S (1994) Sequential operation ofdisconnected cerebral hemisperes in split-brain patientsNeuroReport 5 2381ndash2384

Poldrack R A Desmond J E Glover G H amp Gabrieli J DE (1999) Functional specialization for semantic andphonological processing in the left inferior prefrontal cortexNeuroimage 10 15ndash35

Posner M I amp Petersen S E (1990) The attention systems of


the human brain Annual Review of Neuroscience 1325ndash42

Pylyshyn Z W amp Storm R W (1998) Tracking multipleindependent targets Evidence for a parallel trackingmechanism Spatial Vision 3 179ndash197

Rafal R D (1994) Neglect Current Opinion in Neurobiology4 231ndash236

Raichle M E MacLeod A M Snyder A Z Powers W JGusnard D A amp Shulman G L (2001) A default mode ofbrain function Proceedings of the National Academy ofScience USA 98 676ndash682

Rushworth M F S Hadland K A Paus T amp Sipila P K(2001) Role of the human medial frontal cortex in taskswitching A combined fMRI and TMS study Journal ofNeurophysiology 87 2577ndash2592

Schumacher E H Seymour T L Glass J M Fencsik D ELauber E Kieras D E amp Meyer D E (2001) Virtuallyperfect time sharing in dual-task performance Uncorkingthe central cognitive bottleneck Psychological Science 12101ndash108

Schumacher E H amp DrsquoEsposito M (2000) Neuralimplementation of response selection in humans as revealed

by localized effects of stimulusndashresponse compatibility onbrain activation Human Brain Mapping 17 193ndash201

Shulman G L Fiez J A Corbetta M Buckner R L MiezinF M Raichle M E amp Petersen S E (1997) Commonblood flow changes across visual tasks II Decreases incerebral cortex Journal of Cognitive Neuroscience 9648ndash663

Singer W (1993) Synchronization of cortical activity and itsputative role in information processing and learningAnnual Review of Physiology 55 349ndash374

Smith E E amp Jonides J (1997) Working memory A viewfrom neuroimaging Cognitive Psychology 33 5ndash42

Van Veen V Cohen J D Botvinick M M Stenger V A ampCarter C S (2001) Anterior cingulate cortex conflictmonitoring and levels of processing Neuroimage 141302ndash1308

Wagner A D Maril A Bjork R A amp Schacter D L (2001)Prefrontal contributions to executive control fMRI evidencefor functional distinctions within lateral prefrontal cortexNeuroimage 14 1337ndash1347

Wojciulik E amp Kanwisher N (1999) The generality of parietalinvolvement in visual attention Neuron 23 747ndash764


(Pashler 1994) If a central bottleneck affects RS but notperceptual processing (Pashler 1994) then to the ex-tent that functionally distinct processes engage distinctbrain regions (Kinsbourne 1981) at least some of thebrain regions involved in RS should not also be engagedby perceptual processing However if a central bottle-neck affects both RS and perceptual processing (Arnellamp Duncan 2002 DellrsquoAcqua amp Jolicoeur 2000) thenbrain regions involved in the two tasks may be largelysimilar We used a regions-of-interest (ROI) approachfirst functionally identifying brain regions involved in RSin a localizer scan and then asking whether theseregions are engaged by perceptual processing

RESULTS

Behavioral Data Collected During Scanning

Figure 1 shows the task used in Experiment 1 Table 1shows mean RT and accuracy collected during scanningfor all experiments Increased difficulty in perceptualprocessing led to slower RT and poorer accuracy in boththe length discrimination (Experiment 1) and the color-

matching (Experiment 2) tasks There was also a signif-icant drop in performance during the more difficultcondition in the word task (Experiment 3) These dataconfirmed that our manipulation of the difficulty ofthese tasks was successful

Experiment 1 Length Discrimination Task

Whole-Brain Activation Map for Perceptual Processing

In the random effects analysis on the whole brain thecontrast of Fine versus Coarse length discriminationreveals activation in the parietal regions running alongthe intra-parietal sulcus (IPS) extending into the supe-rior parietal lobule (SPL) in the superior frontal regionsnear the frontal eye fields (FEF) bilaterally and in thebilateral dorsal and ventral lateral prefrontal cortex andthe frontal operculuminsula There was also significantactivation in occipitalndashtemporal regions

We also scanned the same subjects in a RS taskinvolving visualndashmanual mapping Two conditionsmdashcompatible and incompatible response mappingmdashweretested We created a statistical map for incompatibleminus compatible mapping To visualize the relation-ship between the two contrasts we overlaid the activa-tion map for visual RS (in red) and perceptualprocessing (in blue) and highlighted the common acti-vations in green (Figure 2) This activation map reveals astriking degree of overlap Activation in the parietalregions was similar for the two contrasts Other over-lapping regions include the FEF the lateral prefrontalcortex and the frontal operculum The stunning degreeof overlap suggests that many brain regions are com-monly engaged in RS and perceptual processing andthus do not show the response profile expected of theRS bottleneck

RS ROI Analysis Do Any Brain Regions Act as RSBottleneck

The ROI analysis permits us to ask in a more focusedfashion and with correspondingly greater statistical pow-er whether any of the regions involved in RS fail to showan activation for perceptual processing as expectedfrom the behavioral literature To address this question

Table 1 Behavioral Performance During Scanning

Accuracy () RT (msec)

Experiment Difficult Easy SE p Difficult Easy SE p

1 Length discrimination 72 97 4 0001 515 349 16 0001

2 Color discrimination 69 98 4 0001 518 404 24 001

3 Word 84 97 3 002 1283 813 30 0001

Localizer scana 94 95 2 ns 561 383 22 0001

aData were taken from Jiang and Kanwisher (2003)

Figure 1 Sample displays (AndashD) and instruction displays (EndashF) usedin the localizer scans and in Experiment 1 The target is the line in aunique length on each display Perceptual discrimination was tested bycontrasting coarse discrimination (A and B) against fine discrimination(C and D) a natural mapping rule (E) was used during instructions inboth conditions RS was tested on displays of coarse discrimination(A and B) only by contrasting natural mapping (E) against unnaturalmapping (F)




















aIPS 015046 011027 010055 000019

pIPS 009036 000020 011057 003023

FEF 021040 017035 015041 013027




GFi 012045 005022 NA



p lt 05

p lt 01

p lt 001




















aIPS 000015 016028 008029 007023


FEF 016018 ns 020034 015021 014022




GFi 017033 006016 NA



p lt 05

p lt 01

p lt 001










Negative Activation









aIPS 010 024 010 043 010 031 iexcl002 002 ns


FEF 023 039 014 025 018 035 003 010


Operculum 004 008 ns 012 045 018 028 ns 012 045


GFi 005 020 030 072 NA



p lt 05

p lt 01

p lt 001



Error p Level




iexcl008 018 010 02

2 ColorMatching

iexcl008 021 007 001

3 Word iexcl006 028 005 001









Laterality Effects







3 Word 001 009 003 017




3 Word iexcl008 005 005 029






DISCUSSION












p lt 05

p lt 01

p lt 001

















METHODS

Subjects


Testing Procedure


Scan Composition




Materials and Tasks




















Activation Map






Acknowledgments




REFERENCES























































































aIPS 015046 011027 010055 000019

pIPS 009036 000020 011057 003023

FEF 021040 017035 015041 013027




GFi 012045 005022 NA



p lt 05

p lt 01

p lt 001




















aIPS 000015 016028 008029 007023


FEF 016018 ns 020034 015021 014022




GFi 017033 006016 NA



p lt 05

p lt 01

p lt 001










Negative Activation









aIPS 010 024 010 043 010 031 iexcl002 002 ns


FEF 023 039 014 025 018 035 003 010


Operculum 004 008 ns 012 045 018 028 ns 012 045


GFi 005 020 030 072 NA



p lt 05

p lt 01

p lt 001



Error p Level




iexcl008 018 010 02

2 ColorMatching

iexcl008 021 007 001

3 Word iexcl006 028 005 001









Laterality Effects







3 Word 001 009 003 017




3 Word iexcl008 005 005 029






DISCUSSION












p lt 05

p lt 01

p lt 001

















METHODS

Subjects


Testing Procedure


Scan Composition




Materials and Tasks




















Activation Map






Acknowledgments




REFERENCES























































































aIPS 000015 016028 008029 007023


FEF 016018 ns 020034 015021 014022




GFi 017033 006016 NA



p lt 05

p lt 01

p lt 001










Negative Activation









aIPS 010 024 010 043 010 031 iexcl002 002 ns


FEF 023 039 014 025 018 035 003 010


Operculum 004 008 ns 012 045 018 028 ns 012 045


GFi 005 020 030 072 NA



p lt 05

p lt 01

p lt 001



Error p Level




iexcl008 018 010 02

2 ColorMatching

iexcl008 021 007 001

3 Word iexcl006 028 005 001









Laterality Effects







3 Word 001 009 003 017




3 Word iexcl008 005 005 029






DISCUSSION












p lt 05

p lt 01

p lt 001

















METHODS

Subjects


Testing Procedure


Scan Composition




Materials and Tasks




















Activation Map






Acknowledgments




REFERENCES













































































Negative Activation









aIPS 010 024 010 043 010 031 iexcl002 002 ns


FEF 023 039 014 025 018 035 003 010


Operculum 004 008 ns 012 045 018 028 ns 012 045


GFi 005 020 030 072 NA



p lt 05

p lt 01

p lt 001



Error p Level




iexcl008 018 010 02

2 ColorMatching

iexcl008 021 007 001

3 Word iexcl006 028 005 001









Laterality Effects







3 Word 001 009 003 017




3 Word iexcl008 005 005 029






DISCUSSION












p lt 05

p lt 01

p lt 001

















METHODS

Subjects


Testing Procedure


Scan Composition




Materials and Tasks




















Activation Map






Acknowledgments




REFERENCES












































































Laterality Effects







3 Word 001 009 003 017




3 Word iexcl008 005 005 029






DISCUSSION












p lt 05

p lt 01

p lt 001

















METHODS

Subjects


Testing Procedure


Scan Composition




Materials and Tasks




















Activation Map






Acknowledgments




REFERENCES









































































DISCUSSION












p lt 05

p lt 01

p lt 001

















METHODS

Subjects


Testing Procedure


Scan Composition




Materials and Tasks




















Activation Map






Acknowledgments




REFERENCES




















































































METHODS

Subjects


Testing Procedure


Scan Composition




Materials and Tasks




















Activation Map






Acknowledgments




REFERENCES





































































Materials and Tasks




















Activation Map






Acknowledgments




REFERENCES








































































Activation Map






Acknowledgments




REFERENCES





































































Common Neural Mechanisms for Response Selection and ...

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