The central executive and working memory : a dual-task investigation of the N-back task

113 Pages·2000·3.9 MB·English

by  Simmons, Michelle R.

THECENTRALEXECUTIVEANDWORKINGMEMORY:
ADUAL-TASKINVESTIGATIONOFTHEN-BACKTASK
By
MichelleR.Simmons
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
2000
Thisdissertationisdedicatedtomymother,CherylA.Levy. Shehasalwaysencouraged
metostrivetodomybestandtovalueeducationandlife-longlearning. Shehasalways
expressedfaithinmyabilitiesandmademefeeltheprideshehasinmy
accomplishments. Iwouldliketothankherforallthesacrificesshehasmadeforme,her
encouragementofmypursuits,heracceptanceofmyfailuresandshortcomings,andher
love.
ACKNOWLEDGMENTS
Anumberofindividualscontributedconsiderablytodifferentaspectsofthis
work. Iwouldliketogratefullyacknowledgethesupportandguidanceofmyadvisor,
IraFischler. Throughoutmygraduatecareerhehasneverfailedtotreatmeasa
colleagueandcollaborator,alwaysshowingrespectformyinterests,thoughts,andideas.
Hehasassistedinmyintellectualandscientificdevelopmenttoanextentthathemay
neverknow. Iwouldliketothanktheothermembersofmydissertationcommittee,Lise
Abrams,KeithBerg,ChrisJanelle,andBobSorkin,fortheirtutelage,direction,and
constantpatience. ThanksalsogototheCollegeofLiberalArtsandSciencesfor
awardingmeadissertationfellowshipthathaspartiallysupportedmewhileIconducted
thisresearch. Thisprojectcouldnothavebeencompletedwithoutthecomputer
programmingexpertiseofWilliamLowenthalorthemuch-neededhelpofMeredith
Kelleywhoprovidedassistancewithsubjectrecruitmentandtesting. Iwouldalsoliketo
thankRichardMarshforprovidingthePascalcodethatcalculatedtherandomgeneration
redundancymeasureforthethirdexperiment,MeredythDanemanforprovidingthe
stimuliandinstructionsforherListeningSpantask,andtheUniversityofFlorida's
PsychologyClinicforprovidingmewithamodeloftheCorsiapparatus. Specialthanks
gotomydearlove,VincentvanVeen,whohasprovidedemotionalsupportthroughout
graduateschoolandhasservedasasoundingboardformythoughts.
iii
TABLEOFCONTENTS
page
ACKNOWLEDGMENTS
ABSTRACT
INTRODUCTION
TheoriesofAttention
FilterTheories
ResourceTheories
TheNorman-ShalhceModel
TheAnteriorAttentionSystem 1
Baddeley'sModelofWorkingMemory
ThePhonologicalLoop
TheVisuospatialSketchpad
TheCentralExecutive
InvestigationsoftheCentralExecutive
ThePsychometricApproach
TheNeuropsychologicalApproach
Stroop
WisconsinCardSortingTest
ContinuousPerformanceTasks
TheExperimentalApproaches
RandomGeneration
ExecutiveControlandProspectiveMemory
UpdatingWorkingMemory
Then-BackTask
ThePresentInvestigation
EXPERIMENTONE
Method
Participants
MaterialsandApparatus
Verbalworkingmemoryspantask
Visuospatialworkingmemoryspantask
A^-backtasks
iv
Procedures 42
Workingmemoryspantasks 42
A^-backtasks 43
Results 45 »
WorkingMemorySpanTasks 45
A^-backTasks 47
Discussion 49
Figures 54
EXPERIMENTTWO 56
Method 57
Participants 57
MaterialsandApparatus 57
Procedures 57
Results 58
WorkingMemorySpanTasks 58
A^-backTasks 62
Discussion 64
Figures 69
EXPERIMENTTHREE 71
Method 73
Participants 73
MaterialsandApparatus 74
Procedures 75
Results 78
Discussion 81
Figures 85
GENERALDISCUSSION 88
APPENDIXSTIMULIANDINSTRUCTIONS 93
StimulusSentencesforDanemanandCarpenter'sListeningSpanTest 94
StimuliandApparatusfortheModifiedCorsiBlock-tappingTask 96
InstructionsfortheRandomKeypressGenerationTask 97
REFERENCES 99
BIOGRAPHICALSKETCH 104
V
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
THECENTRALEXECUTIVEANDWORKINGMEMORY:
ADUAL-TASKINVESTIGATIONOFTHEN-BACKTASK
By
MichelleR.Simmons
August2000
Chairman: IraS.Fischler
MajorDepartment: Psychology
Workingmemoryisthoughtofasacognitiveprocesscapableofbrieflystoring
andmanipulatinginformation.Workingmemoryconsistsoftwodomain-specificslave
systemsandacentralexecutive,whichisresponsibleforcoordinatingthissimultaneous
storageandmanipulationofinformationandotherexecutivefunctions. The/i-backtask
isanexperimentaltaskthatrecentlyhasbeenusedtoexaminetheneurophysiological
substratesofworkingmemory.Inthen-backtask,participantsarepresentedwithaseries
ofstimuliandaretoindicatewhetherthecurrentstimulusmatchesthestimuluspresented
nstimulibackintheseries,wherenequalsanumberbetween0and3.Theresultsof
theseneuroimagingstudiessuggestthatthen-backrequiresexecutivecontrolathigher
levelsof«,butnotatlowerlevelsofn. Thishypothesiswastestedin3experimentsin
whichparticipantswereaskedtoperformversionsoftheAz-backtaskconcurrentwith
vi
secondarytasksdesignedtotaxthevariouscomponentprocessesofworkingmemory. In
experiment1,anauditory-verbaln-backwaspairedwithavisual-spatialversionofthen-
back.Relativetothesingle-taskconditions,thedual-taskconditionsproducedmarked
interferenceinthe2-and3-backtasks,butnotinthe0-and1-backtasks. Inexperiment
2,theverbalandspatialn-backswereagainpairedbutthelengthoftimebetweenstimuli
wasshortenedinordertotestatime-sharinghypothesisregardingtheresultsof
experiment1. Theaccuracyresultsreplicatedtheresultsofexperiment1,butthe
reactiontimedatashowedinterferenceinthe1-,2-,and3-backtasks.Inexperiment3,
theauditory-verbaln-backwaspairedwiththreevisualtasks:arhymetask,arandom
keypresstask,andamentalrotationtask. Theresultsfromthesedual-taskpairings
indicatethattheresultsfromexperiments1and2mayreflectmeredifficultyratherthan
theneedforcentralexecutiveresourcesspecifically. Takentogethertheresultsofthese
experimentsleadtotheconclusionthatthen-backtaskisacomplextaskthatrelieson
multipleprocesses,someofwhichcanbeconsideredexecutiveprocessesandothersthat
arelessexecutiveinnature.
vii
CHAPTER
1
INTRODUCTION
Executivefunctionsappearcentraltoanyintelligenthumanbehavior.Ourability
toexertcontroloverourattention,memory,andactionsseemstobeattheheartofour
conceptionofourselvesasindependentagentshavingfreewill,ratherthanmerely
reactivebeingswhosebehaviorsareshapedentirelybytheenvironmentinasimple
stimulus-responsefashion. Thisdissertationrepresentsanattempttoexaminetheroleof
executivefunctionsinworkingmemorybypairingvariousversionsofthen-backtask,a
workingmemorytaskthathasbeenusedrecentlyinneuroimagingstudies,withseveral
secondarytasksintendedtotaxthemultiplesubcomponentsofworkingmemory.
Despitetheclearimportanceofexecutivefunctions,thedefinitionofexecutive
function,orexecutivecontrol,iselusiveanddependsonone'stheoreticalorientationor
specificsubfieldwithinpsychology. Infact,Eslinger(1996)statesexplicitly,'Thereis
nouniversaldefinitionofexecutivefunctions"(p.380). Barkley(1997)underscoresthis
moreorlessuniversalfrustrationbylamenting,
...whatprocessisitthatdetermineswhichgoalswillbe
selected,whichplans,rules,andothersourcesof
informationwillbeconsideredinsupportofthem,and
whatformsofprivateself-directedactionsarenecessaryto
generatethatinformation?Thatprocesshasbeenlabeled
thecentralexecutive...yetitsspecificationhasbeenleft
ambiguous. Ithas,alasbecometheblackboxwithinthe
1
2
blackboxthatinformationprocessingmodelsofcognition
havebeenattemptingtoexplain...(pp.201-202).
Regardlessofthefrustrationandthelackofoneuniversaldefinition,many
attemptshavebeenmadetodefineexecutivefunction,andtheseattemptsofteninclude
wordsandphrasessuchasplanning,goal-directedbehavior,strategyselection,temporal
sequencing,anticipation,andpreparationforaction. Onoccasion,executivefunctions
havebeenequatedwiththosefunctionscarriedoutbythefrontallobesofthebrain,
whichprovestobeaninadequatedefinition,atbest. WelshandPennington(1988)
includeintheirdefinitionofexecutivefunctions,holding"amentalrepresentationofthe
task,includingtherelevantstimulusinformationencodedinmemoryandthedesired
futuregoalstate"(p.202).Whicheverspecificdefinitionofexecutivefunctionisused,it
isclearthatexecutivefunctionslieattheintersectionofmemoryandattention.
Thisprojectfocusesprimarilyononeparticularconceptualizationofexecutive
processes,namelythecentralexecutiveofBaddeley's(1986)modelofworkingmemory.
Firstsomeoftheimportantideasrelatedtoexecutivecontrolaredescribed,followedbya
shortsketchofBaddeley'smodelofworkingmemory. Finally,someofthewaysin
whichthecentralexecutivehasbeeninvestigatedareoutlined.
TheoriesofAttention
Laterinthispaper,thecentralexecutiveisreferredtoasan"attentional
controller."Thereforewhatismeantby"attention"needstobedelineatedsothatthe
phrase"attentionalcontrol"hasmeaning.Mostarefamiliarwiththeinsightfulquote
fromWilliamJames(1890):
Everyoneknowswhatattentionis.Itisthetaking
possessionbythemind,inclearandvividform,ofoneout
ofwhatseemseveralsimultaneouslypossibleobjectsor
3
trainsofthought. FocaUzation,concentrationof
consciousnessareofitsessence.Itimplieswithdrawalfrom
somethingsinordertodealeffectivelywithothers,(pp.
403-404;citedinAbemethy,1993).
Indeed,ineverydaylanguage,everyonedoesknowwhatattentionis. Ateachertellsa
daydreamingstudenttopayattentiontoherlecture. Ifwenoticesomethingnewinthe
environment,thatstimulushasgrabbedourattention. Ifwearethinkingaboutthemeal
wearepreparingandthenbeginthinkingaboutabillthatneedstobepaid,wehave
turnedourattentiontothebills. Ifataskweareengagedinisdifficult,weknowthatwe
mustdevoteourfullattentiontoitorelsewearelikelytomakeamistake. Wetalkabout
afriendwhohasashortattentionspan. Intheseeverydayexpressionswhichnoneofus
hasanytroubleunderstanding,weseethemultitudeoftasksthatJamessonicely
summarizedas"withdrawalfromsomethingsinordertodealeffectivelywithothers."
Unfortunately,despitethefactthateveryoneknowswhatattentionis,noone
reallyknowswhatattentionis(Pashler,1996). Withincognitivepsychology,thereisno
oneuniversaldefinitionofattention. Theonlyuniversallyacceptedidearegarding
attentionseemstobethatitislimited. Attentionhasbeenequatedandassociatedwitha
numberofotherconcepts,includingorienting,mentaleffort,andconsciousness. Aswith
executivefunctions,thereareamultitudeofparadigmsandtopicsofinterestthatinvolve
attention(e.g.,selectiveattention,visualattention,auditoryattention,spatialattention,
sustainedattention,vigilance,preparatoryattention,anddividedattention). The
considerationofattentioncanbedividedbroadlyintotwoclasses:attentiontoour
environmentwiththepurposeofbringinginformationinthroughthesenses;and
attentiontoourgoalsandintentionswiththepurposeofcarryingoutsomeaction,
whethercovertorovert. Theefficientandaccurateoperationofbothformsofattentionis