When co-action eliminates the Simon effect: Disentangling the impact of co-actor' s presence and task sharing on joint-task performance.

Thisstudyaimedatassessingwhetherthemerebeliefofperformingataskwithanotherperson,whoisinchargeofthecomplementarypartofthetask,issufficientfortheso-calledjointSimoneffecttooccur.Inallthreeexperimentsofthestudy,participantssataloneinaroomandunderwenttwoconsecutiveGo/NoGotasksthatwereidenticalexceptfortheinstructions.InExperiment1,participantsperformedthetaskfirstindividually(baselinetask),andtheneitherco-actingwithanotherpersonwhorespondedfromanunknownlocationtotheNoGostimuli(jointtask)orimagingthemselvesrespondingtotheNoGostimuli(imaginativetask).Relativetothebaseline,theinstructionsoftheimaginativetaskmadetheSimoneffectoccur,whilethoseofthejointtaskwereineffectiveinelicitingtheeffect.Thisresultsuggeststhatsharingataskwithapersonwhoisknowntobeinchargeofthecomplementarytask,butisnotphysicallypresent,isnotsufficienttoinducetherepresentationofanalternativeresponseabletoproduceinterference,whichhappensinsteadwhentheinstructionsexplicitlyrequiretoimaginesucharesponse.Interestingly,weobservedthatwhentheSimoneffectwasalreadypresentinthebaselinetask(i.e.,whentheresponsealternativetotheGoresponsewasrepresentedintheindividualtaskduetonon-socialfactors),itdisappearedinthejointtask.Weproposethat,whennoinformationabouttheco-actor’spositionisavailable,thedivisionoflaborbetweentheparticipantandco-actorallowsparticipantstofilteroutthepossible(incidental)representationofthealternativeresponsefromtheirtaskrepresentation,thuseliminatingpotentialsourcesofinterference.ThisaccountissupportedbytheresultsofExperiments2and3andsuggeststhatundercertaincircumstancestask-sharingmayreducetheinterferenceproducedbytheirrelevantinformation,ratherthanincreaseit.