已领丨Whydoweintuitivelybelievewe

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　　Itisperhapsthemostfamousexperimentinneuroscience。In1983，BenjaminLibetsparkedcontroversywithhisdemonstrationthatoursenseoffreewillmaybeanillusion，acontroversythathasonlyincreasedeversince。
　　Libet’sexperimenthasthreevitalcomponents：achoice，ameasureofbrainactivityandaclock。
　　Thechoiceistomoveeitheryourleftorrightarm。Iinsomeversionsoftheexperimentitistoraiseyourleftorrightfinger。Libet’sparticipantswereinstructedto“lettheurge〔tomove〕appearonitsownatanytimewithoutanypreplanningorconcentrationonwhentoact”。Theprecisetimeatwhichyoumoveisrecordedfromthemusclesofyourarm。
　　Themeasureofbrainactivityistakenviaelectrodesonthescalp。Whentheelectrodesareplacedoverthemotorcortex（roughlyalongthemiddleofthehead），adifferentelectricalsignalappearsbetweenrightandleftasyouplanandexecuteamovementoneithertheleftorright。
　　Theclockisspeciallydesignedtoallowparticipantstodiscernsubsecondchanges。Thisclockhasasingledot，whichtravelsaroundthefaceoftheclockevery2。56seconds。Thismeansthatbyreportingpositionyouarereportingtime。Ifweassumeyoucanreportpositionaccuratelyto5degreeangle，thatmeansyoucanusethisclocktoreporttimetowithin36millisecondsthat’s36thousandthsofasecond。
　　Puttingtheseingredientstogether，Libettookoneextravitalmeasurement。Heaskedparticipantstoreport，usingtheclock，exactlythepointwhentheymadethedecisiontomove。
　　Thebrainactivityshowedthatthedecisionhadoftenalreadybeenmade，beforetheparticipantswereawareofhavingtakenaction
　　Physiologistshadknownfordecadesthatafractionofasecondbeforeyouactuallymovetheelectricalsignalsinyourbrainchange。SoitwasinLibet’sexperiment，afractionofasecondbeforeparticipantsmoved，areliablechangecouldberecordedusingtheelectrodes。Buttheexplosiveresultwaswhenparticipantsreporteddecidingtomove。Thisoccurredinbetweentheelectricchangeinthebrainandtheactualmovement。Thismeans，assureascausefollowseffect，thatthefeelingofdecidingcouldn’tbeatimelyreportofwhateverwascausingthemovement。Theelectroderecordingshowedthatthedecisionhadinsomesensealreadybeenmadebeforetheparticipantswereawareofhavingtakenaction。Thebrainsignalswerechangingbeforethesubjectiveexperienceoftakingadecisionoccurred。
　　Westruggletodescribeourthoughtsandfeelingsaccurately，makingitdifficulttotellwhenwehavemadeadecision（Credit：iStock）
　　Hadparticipants’brainsalreadymadethedecision？Wasthefeelingofchoosingjustanillusion？Controversyhasragedeversince。Thereisfarmoretothediscussionaboutneuroscienceandfreewillthanthisoneexperiment，butitssimplicityhasallowedittocapturetheimaginationofmanywhothinkourstatusasbiologicalcreatureslimitsourfreewill，aswellasthosewhoarguethatfreewillsurvivesthechallengeofourmindsbeingfirmlygroundedinourbiologicalbrains。
　　PartoftheappealoftheLibetexperimentisduetotwopervasiveintuitionswehaveaboutthemind。Withouttheseintuitionstheexperimentdoesn’tseemsosurprising。
　　Thefirstintuitionisthefeelingthatourmindsareaseparatethingfromourphysicalselvesanaturaldualismthatpushesustobelievethatthemindisapure，abstractplace，freefrombiologicalconstraints。Amoment’sthoughtaboutthelasttimeyouweregrumpybecauseyouwerehungryshattersthisillusion，butI’darguethatitisstillapersistentthemeinourthinking。Whyelsewouldwebetheleastsurprisedthatitispossibletofindneuralcorrelatesofmentalevents？Ifwereallybelieved，inourheartofhearts，thatthemindisbasedinthebrain，thenwewouldknowthateverymentalchangemusthaveacorrespondingchangeinthebrain。
　　Thesecondpervasiveintuition，whichmakesussurprisedbytheLibetexperiment，isthebeliefthatweknowourownminds。Thisisthebeliefthatoursubjectiveexperienceofmakingdecisionsisanaccuratereportofhowthatdecisionismade。Themindislikeamachineaslongasitrunsright，wearehappilyignorantofhowitworks。Itisonlywhenmistakesorcontradictionsarisethatwe’redrawntolookunderthehood：Whydidn’tInoticethatexit？HowcouldIforgetthatperson’sname？Whydoesthefeelingofdecidingcomeafterthebrainchangesassociatedwithdecisionmaking？
　　There’snoreasontothinkthatwearereliablereportersofeveryaspectofourminds。Psychology，infact，givesuslotsofexamplesofwhereweoftengetthingswrong。ThefeelingofdecidingintheLibetexperimentmaybeacompleteillusionmaybetherealdecisionreallyismade‘byourbrains’somehowormaybeitisjustthatthefeelingofdecidingisdelayedfromouractualdeciding。Justbecauseweerroneouslyreportthetimingofthedecision，doesn’tmeanweweren’tintimatelyinvolvedinit，inwhatevermeaningfulsensethatcanbe。
　　MoreiswrittenabouttheLibetexperimenteveryyear。Ithasspawnedanacademicindustryinvestigatingtheneuroscienceoffreewill。Therearemanycriticismsandrebuttals，withdebateragingabouthowandiftheexperimentisrelevanttothefreedomofoureverydaychoices。EvensupportersofLibethavetoadmitthatthesituationusedintheexperimentmaybetooartificialtobeadirectmodelofrealeverydaychoices。Butthebasicexperimentcontinuestoinspirediscussionandprovokenewthoughtsaboutthewayourfreedomisrootedinourbrains。Andthat，I’dargue，isduetothewayithelpsusconfrontourintuitionsaboutthewaythemindworks，andtoseethatthingsaremorecomplexthanweinstinctivelyimagine。