B5 SpHtDecisions
GEORGE \VOLFORD) N,IICII{EL B. NIILLER, AND \IICFL.\EL S. GAZZAT\IGA
.\B: rR.\, r ::ril-irlain patients provide a lascinating look at some The split-brainoperation ,,;' tir, r..,:,. .irrr,trncling consciousness.lVe bricfl1' rL-viewpirst lin,i:ir..l-.,:r,: r:r..rghrsgained lrom studying thcsc patients. l\:€ Split-brain surgery is a treatment for certain tvpes o1' ill:( i.:. ::. r-.,,r,'cictail some of thc more irrteresting(ar us) findines intractable epilepsri Seizures in epilepsv are causecl bl.an .irr., 'lr.' ..,': cclition of this volurne. \\r conclude bl ruqgestinge abnormal electrical discharge that leads to a reverberating rrrr'r:ifltcL rer-sion of signal cletectiontheorv that mav shed some ii{l;r ,,rr aspcctsof consciousnessir thcse paticnts. or rhvthmic dischzrrge.In some individuals, the rhrthmic dis- charges recruit tissr,rein both l-remispheres.The split surgerv ( ' .,lri//d-rJin tlrcsplit brain involves severing all or part of the corpus callosum. the m:rjor fiber tract connectine the tr,r'or:erebral hen-risphercs, ,irr n:rtient. nll- I .._.-^ r*,-_^--_ _--e.f a Llnlqlle perspecuve on some and on occasion other {brcbrain commisures as rvell. The ': .- l{ conscious experienc:e.and pcrhaps on the nature corpus callosum is the largcst fiber tract in the brain. f'he ri.ciousness itself. Rogel Sperr',' once relerred to the human corpus callosum contains about 200 million axoris. "tu,o : ,\ separate realms o1' conscious a$'areness;t\'vo originating lrom layer 2/3 pyranriclal ncurons (r\boitiz et al.. :r:.- -. perceiving, thinkine arrd rernernbcring systtms." 1992). The first reported usc of' splittins the corpus cailo- 'i-l;' : nr-r'i'carh'ft'ar.sthrrt scvcringthe callosr"rmrvas:r bad surn to control epilepsv '"vasbv \hn !\'ascncn ancl Herren i I l89 r.**t , rn1r.l poLtion of the corplls cailosunr. In theorv, paticnts that ltoth hemispheres of tr,vosplit-brain patients (one r,vith rrlr,, Iriive ulr.lcrqonc :r complete callosotonrylblrn :rn icleal a con-rpletesplit, the othcr ir parti:1l split) coulcl cliscliminate P,,Pu1.rri.rr firl stuclvingthe inclepenclentlrutctioning of thc nvo ob.jectsu'ith dillcrcnt ick:ntitics cc1uall,vr,r'ell, but th:rt the rr'r irt-nrisplrclc:.]n plir-r:ti<-e,onlv a rclativelv srnall pcr- right her-nispl-rcrcpcrformed better than the lclt hcmisphcrc ( r-nrllgr ,l tht'se irntirrLts -rle eppropriete tbr behavirtral in discliminatins tr,voic1cntical objects r,vith diflcrent spatial srllrlies.,\ll ol' tlrt: P:rtit:ntshalc hacl a long histon' of' scvcre locations. In subsequent str-rdiesthe-v lirund tlrat the right cpiLeptic -.rizrrrt'.. atrcl nitnv sr"rller liom other cognitive hemisphere !\ras better zrt line oricntation and vernier dcficits. Althougir rt:lativcll' rarc. thcrc :1re morc split-l-rrain :rcuiq.,but that both hemispheres performed equallv well in paticnts than there arc p.itients lbr manr, of the other inler- sizc comparisons and lr-rminar-rcediscrirnination (Corbaliis, esting brziin anomalies. Funnell, and Gazzaniea. i 999, 2000a). Furtherrlore. Corballis ancl colieagucs havc sr-rggested Htmisphericlsymme tries thart these hemisphcric asrrrmctries in visuospatial process- ing are not erntirL-lvdue to hemispheric specializations for Since at least the tinre o{' Broca, rve have believed that somc particuiar hpes of sensory input bi-rtinvolve lateralization of behavioral functions snch as language are lateralized in the spccilic tl?cs of processing, such as visual groupins. One brain. Brocir studied a patient ."vho r'r'asparurlvzed on the piece o{'er.'iclcncclor this idea involves the line motion ellect. right side and hacl lost the abilitv to speak. The man died This occurs u'hen a line is presented briefly bet'"veen tr,vo shortl,v thercafter, zrnd his brain rvas prcscn'ed. Nlost of our sqLlares.Just prior to the appezrranceof the line, one of the kno',vleclee allout hcn-rispheric asyrnrnetrics or.-el the next squaresflashcs. To observers, it appears that thc line is prop- century camc lrom studr,'ing people rvith varior-rsnpes of asatins lrom the flashing square- Hil 1190 co\scrlousNEss -Ihi'sr'r'()ncl it tor-rcherlthe sr:t:orrt1rli:k. cliskthcn rrror,ed tcsted)in therfieicl crl-artcnti{)lt sincc rhe start of' thc posncr an'at' fionr tlrr flr'.t rli.k. I' ) nl()sl (,1)srrvcrs.it tvoLildi1ppe21r cuirrg p:rradism in thc 1!)70s(I{irrgstonc et al., in pr.css). tlrat the nl()\('l',',r'nl,,1 rllr' :r'tori,l riisk is c:rLrscc,lltr,. tlrc fir.st disk. H,,r'r'r, r'.li ., irtrg,-(.111)Lrgh gaP. either sltatialor trnr- Nl EuIon' Hernispl-rcrics1.rt:cial iz:ition in particul;rr low -lt:vcl por':il.i' irtr,r'',',1 i,,-".r,,,1 tlt,'1r9 rti.cics.the ntoti'' oi-t6e cognitirre processes czrn afi'ect episoclic rncnlorv fonn:rticrn, tli.kr cl,,r. : l ,r1)pr'.u( :rLr)iriLvrelatcd. The left hcrnisphcre thc memorv tbr real-n orlcl events,as '"vell. Re trieving episoclic of- rt :pirt-lrr11;.;,.1';1';'r..J.\\.. r,r,as inclifli:retrt to the rnan\tu- nremories o{ten involves decisir-rnprocesses that are allectccl Ilrti,,rl,,i ::. :r.,tr,ii iri, r,r1'tlrceap, but the right hctnisphere bv a vzrrietyof infiuences, jusr like any other ciecisiorproccss. l-r':ll'ir.,. ,. :' .tili.rrrr:rllrv the magnitucic of the eaps in ;Ln ancl the r.rnderlyine brairr resions engasccl during retricval .!lll l: ...;.;,,rrl{l:r'r eI aL..iri pr,.st.. can v:rrv greatlv fi'orn subject to subjcct, clepenclinertn incli- ., I)' ,-,' nght hcmispherc adr,antzrge1br some {brms viclual strategies (Nlilier ct al., 200 1; Nfillcq Kinsstone. -: ,,t.-, ..:r.,1proccssinq ancl cvidencc lbr a righr hemi- ancl (]azzanign. 2002; \\'indmann. Urbach, and Kutils. \i,'.r' ,':llletefi :. there are some visual processcsin which 2002). T'hc encodins of episodic memorics. as opposeclto !ll,' .,lr irlnrisphere has an advantage. Fcr example, reccnt retliev:rl. appcars to bc clicit more consistent neural actir,a- Il(' I'rr:r',rLginqstuclies have shor^,nthrt nrcntallv rotating an tioris :rcross subjects (hrr leview, see Clzrbczaand Nvbere, .:,tirntcs parietal and liontai rcgions it'r botlt hemi- 2000). Hernisphcrit: asvnrmetriesplav a rt.rlt:irr memorv fbr- - : 'Litthat imagining yourseil' in a clitlerent spatial per- nration, zrsevidcnced bv nenropsvchokrgit:al studies (N{iLter: ' :,'lative to :rn oltjcct mar.' inrolr.c clillt:rent ltarit:tzrl (-lorkin. and lhrcbcr, 1968; NIilner, 1972)and more rcccnrlv :.:.Ljlcgions lc-rcatcdprimririlr- irr the lcii hcrnisph.re by neuroirnaging stuclies (Tulving et zrl., 1994; Kellc_v (.hurcl'r, 'flrlvins. ,. and Badre.2()01: Zacks et al..2002,. et al., 199t3; Nybcrg, Catrcza. ancl 1998t \Vzrgner .,;Lclcolleagr.res have tcsttcl tlris distinction in a split- et al.. 1998; Nvbcrg et al., 2000). Florvevcr,manv nlentorv ' r:r.nt using a paradigm in rvltich an identical stimLr- researchersdebate the nature of those asvnmetries. Sonre :. ire nrent:rilv rot:rtecior inrugint'ci fiorn a cli{ibrent investigators have arsued that episoclic encoding is prcdonr- -1-lrer' ,r:r". lbr-rnclrhat rrlrilc rlrt' riq-ht hcnrispher.t. in:rrtly a lell prcli-ontal liurction ancl that episodic retrieval ilppclilr r: t() l)e bctt('r irt tlli'ntlIl t()l,tli()]t. thr-' leli herni- is predonrinantlv a right pre{iontal lunction ('Ir-rlving ct al.. sphcre.rr)l)r'arc{i tr l r, 1x'rrcr' :ri ])('rspccti\:Lrtakine (Funncll, 1994). Typiirally thcsc neuroimasins stuclics rely orr thc (iezzlrriilrL. J,,rhns,,tr.,rnrl ltt(-)I . encocling and retrieval o{- lamiliar verbal marerial (Clabcza Iirr thr'-.crclati.,ch' iurr-lt:r'cl perccptr-ralparadiunrs. tht arrd Nylterg, 2{J00).Other researchershave susqestcclrhrLt hcrni-.phcric asvnrmetries api)c:rr to berclriven bv top-dorvn hernispheric etsyrnmetries,particularl_v episodic encocling,ale ploccsscs.ln ccrntrast,nranv hemispheric dill'crenct-slvitlr rnaterial-specificrathcl tharr process-specihc.For exarnplc, highcr-olclcl i'ognitive proL-esscs)such zts attenlion :rncl re ccnt neuroimaging research hirs liruncl precloniinzrntlvrieht |nr'llt()f\. illll)ciir tO bc clrir.'ctrb,v specializertion IOr stin-[rlus lremisphere activations in thc prcttonrrll (]ortex during the propt:r'ries. Kingsronr:. Fr-icscn. :tncl Gazzaniea (2000) pcr- cncodins of unfamiliar f:ices(Kcllc_v et al., 1998) ancl tcxtures lirrnrcd scvtrll iiiscinatirrg stuclics on rt-flexile al.tcniion ftagner et al.. l99ti). Nevertheless,proponents o1'a laterirl- Llsinqcve qazt: dilet'tion in split-brain patients. As in the izcd episodic encodins rcgion zrrglrc thirt thc bulk of neri- Posnt--rcuing palaciigin. a ,scllcrnatic-fhce r,l'asprcscnted as roimaging ,s56;1rch,includine sotne stucliesrrsing nonvcrbal the cuc. The direction of' rhc cvcs inar' ltoint to a targctJor. rnaterial, is consistent rvith cpisodic t:ncocling bcirre pre- it rrlav not. ht thc c::rscof ltlirn:ir'v intcrest, thc direclion of clrrninantly' a left hemispllere proccss (N,vberg,Cabeza. ancl e\.e s2rz(:t\,\'lis llot pt'eclictir.ettl- thc tarqet krcation. Y-etin the Tulving. 1998: Nyberg et al., 2000). right liemispherc. itut nrit tire lcli. the patient r,vastaster tr,r Thc testingof split-brain p:rtientscan pl:Lya role in resolr- respond to a tarscr in tl.rc path r-rf the evc gazc. 1'his effcct ing tl-risclebate. If- encocling ancl r'etrieval arc prcdominantlr, r,vasobtainctl rr'iLli sclrcrruitic 1)rces:rnd with elr:s aLrne, but lirteralized processesin opposite hcmisphercs, tlien split- not whcn the schertratic l-tu:es\\.cre prescntcci upsicle clor,vn blain patients should har,'c nrajor mernofv impairment. (Iigr-rre85.l). lVhen the litcc r.r'asactuallv predictivr: of tarsct be<:trusethc information is cncocleclin one heniisphere arrcl location or w-ht:n thc stinrulus was :r nonpredir:rne zrrrtx,v; rctrievccl by the othcr irr-rclthe two ht:misplrercs 2lre discorr- 'I'hese both hemisphercs shou,ccl a sinilar ellcct. fincling'. nt:ctecl.\'et these patients c-lemonstratt:onlv rninol deficits sllgsest that rcllexive.ioint attt:ntion is nt:cliirtcd bv <.or-tici-rl in episoclic nrernorl.. (Zairlel zrrrcl Spt:rrv: I974: LeDoux pr.rcesscsthat are lutcr-alizeclto tlre heniispht,rlc responsible et al.. 1977;Phelps. Hirst,;rncl Gazzanisa. I991, Ntetr:alfe, {br lace processing. rvhich in thesc rr.vopatients is the rig}rt Funrreli. and Gazzaniga. 1995; sec Viskorrtas, Titiclel. hernisphcrt:. Parcr.rttrcticalh,: lhis r,vork rvith split-brain Knor,vltttn. 20113,lor a recent casc ot' a paricnt rvith more it;Ltit'rrt.ltrl to rhr sur'gtrisingtincling that noltprcdi('tive severe irnpairlnerrts in alrtobir)eraphiciri nremory). Split- ;u r'()\\. clrrlolicnt irtteniion irr rror.nlrlsrrltjccts, a tinclingthat brain paticnts perfbrrn norrnallv on ntost recognitiorr trsts irrrr. r L,iiili t- ti) l lnsit: usslltnl)tion(ltncl ncver c;q;licith' vet oftcn have slieht irnpairnrcnts on fiee rccall tzrsksthat \,VOLFORD] IVIILLER. AND C;AZZANIGA: SPLIT DECISIONS I 191 Left Hernisptrere Right Hernisphere Upright Faces 700 d50 .!, saze effect q 6g0 600 - q, \-J 551) lr"'/' I v 50,1 500 450 F---+ .{00 40t :;it' @.@350 350 congruent incongruent congruent incongruent Gazeto TargetSOA ---o- 100ms --_e- 6oo ms Inverted Faces ?00 * 650 650 o 60D 600 AA a 550 550 v 500 3 450 400 {0'l w.w 350 350 congruent incongruent congruent incongruent EyesOnly ?00 650 650 * a d00 600 Q __^ 550 - s00 500 \./\--lrn l}r o)vv dr\ - + i/ {so 450 400 100 350 congruent incongruent congruent incongruent 6;o16 6li1sc:i*.:";'ii l: ri;r'nr.8r.l The graphs reprcsent split-brain patientJ.W's per- the target r,v:rsin the risht visual {ie1d (left hernisphcre). gaze effcct (responding sig-,-'lt' iL)rlrlulcc. 1-wo Izrces(Lrpright or inverted) or trvo pairs of' evesrvete tion did not predict targ^etloc:rtion. The target locration and gaze, -' prcsented concurt'entlv to the left of a central liration cross and to nificantly {aster to a congluency between '['he lvas eviclent onll in the riqht rhe right of the cross. task rvtrsto maitttain centt'al fuxation and direction than to an incongruency) and eycs. Paticnt \iP had* to press zrleit-hancl ke-vrvhen the tnrg.-tttastcrisk was presented to hcrnisphere. arrd only for Lrprieht laces 200t1). the lclt r.isuiri field (r'ight hcmisphere) and :r rig-ht-hancl kt:y wlien similar resnlts (Kinestone, F-riesen,ancl Clazzzrnig:t, 1192 CONSCIOUSNESS reclr-rire;rclc1itionn1 rcclritnr.ttr, '[' .ft-rttcqic res{ rLtrces (1)hclps. 'fhcsr: Hirst. arrcl (iazzlnisir. ii)9 lt. lindings in split-brain WORDS l)lllirllti \uglp\l il,:rt ,1,lir.rrilnr rlrll on n,'Lrrointugitrg l$0Vo str-rc[it'srttln irrri,rt'rl]re rri:rtr'rial-speciliclather than proccss- n Shallow specilrc. il: :LL!tr\tr(l ll Kt:[cl' ancl col]eagues(1998) ancl 807o c! r Deep !\iagrrr'r :Lrcli ',11tl,lues 1!)9tt). qJ \\r clircciir trstr'ci this hvpothesis bl manipulating the 60Vo encr.,clrn,l,t rrrrr-(l:ancl larcesin cach ht:misphcre o1' two T spiit-i,r'.Lirp.ir.:nr-r. onc \,vitha conrplcte split and thc other 40Vo I rr itlr .r r.r'.r.rL.p1ir ;N'Iiller, Kinestone. anclLiazzaniga, 2002). (, Il' , i,;-, ,ir, ,r,,.r.,clirrgis preclorninirntlva left hemisphere L 207a --l L lirn':r, :. ::rrrtocnclcntof mntcri.rl nPt. then ,rnl,,'the leli r\ I I- hcr:,..r,;,,r, irr tl-rcsepatiellts shouLclbeneflt liom rnore elab- 0Vo oliili , :r! i,ciirtgof worcls and laccs. Hor.vcvel because lan- Left Hemis Right Hemis quaL, :, pr.clcrcr.rtiallylaterzriized to the lelt hernisphcre:rnd 1ii( i' '''sirrsis lateralizedto the riglit hemispherein these rr.,'i, (ilzzaniqa, t"' 2000). rvc hlpothesizecl that the leli r.. 1.,,, .,,., rl.q.qi1J,r .,.,.q(.lt.t**trt-Li,rrr','-h. ql.e}-c r'ni {)(lini ol' lhniliar uorcls. ancl tl'rarthe rieht hcmisphere. llrt not tht: Ieft. r'voLrlclbcncfit lrom the cleeperencocling of' ,ffi unf'unriliar hccs. C)r"rrhlpothesis r,voulclwork only if encod- &€* r inq pr',,c,:s-.cs ncre availablc in both hemispheres. ;\*/""i .\..lr,rrrn in lrgure 85.2.n'e firund in both patierrtsa sie- l00Vo ni{it rrrrt rlill'rcnce in recognition pcr-1br-mancealier deep n Shallow 80Va pror:r:-.srngclrrling cncocling of lvorclsversus shallow pro- ao I Deep ccssinqclurins encodins ol'rvords in the lel'thernisphere. but q, no dillercncr: as iL lirnction of clepthof' encodinq in the rieht 60Vo hcmispircle. L,nlzLnriliarlaccs vicldecl the opposite result. I Therc u':rs a sig-nificant dilibrence in recognition perlbr- 40Vo rrancc zrftercleep cncoc{ing of lirccs versus shallon'encoding U 20Va r-il r of laces in the rielrt hen-risphere,but no dilGrence in the left ;r hcrnisphcre. Our resrrltsclcarly indicatecl that manipulati{)ns r\ tl I of episoclic cncodins c1ifl'erentiallyafl-ect thc pcrfbrmancc of 0Vo the hcrrispheres. clcpcncline on the flpe of material beins Left Hemis Right Hemis processccl. F,ach liernisphcre sccms to be fi-rll1'capable 01' Frcrinr 85.2 The top eraph represcnts recogriition perlirrrnance sllpportinc episoclicmernor)! and some asvnmetries seem [o using words lor the left ancl riglrt hernisphcre s of split-brain patient be b:rsed on the tlpe of matefial being processed.A more J.l\1, r.vhile thc bottoin eraph leplcsents recognition perlormancc :: recent NII{I stricly ol normal sLrbjects rcezrrding hen.ri- using r,rnfainiliar laces. Grav Lrarsreprescnt a shallow levt-l ,ri' pro- (firr spheric asvmrnetlies clr-rringcncoding r-r['f,rcesftVig ct :11.,in cessing clurint encoding worcis: dot-'stlie wrrrcl contlin tl-reletter r.:::. press),along rvith prcvious p:ltient str-rdics(Nlilncr, 1972)ancl a? fbr' {:rces:is the lacc fi.-nrale?i,and bhck ltars represent a cleep -"'.. level of proccssinp (firr n'ords: cloes the lvorcl represerrt :r Livinq sodir-rrnam\tal studies (Keliey et al., 2002), clernonstr-ate olrjcct/ lor laces: is the lirce the lace ol' a healthy personi'). Both the ,T:1 . functioniillv sr:parable routes to memorv r,vithin preinrntal 'l-he *-, study ancl thc test sessiorrswere lateralized to one hemisphere. cortcx tl)at depcncl orr both the intrinsic properties of the to- leii hemisphere's recosrition perlorrnance improved sienificantlr' F-:' be-renembered n-raterialsancl on the spcci{ic coenitive opcr- after deep proccssirre of rvords comparcd to shallow i)rr,ccss;rg, F, ations rcquired bv the task. while the rielrt hemispherc sholved no improvenrent. In contrast to lvolcl plocr:ssing, the right herrrisphcrr:'srccognition per{i.rrrnzrnce *-' \Vic ancl collc:rerrcs(in pr-ess)also sussest that menrolize- irnproved sigrrificantly aficr dccp pror:t:ssirrgcompared to shallow tion of- namzlble (materials r.r'ithflucnt oitjects acccssto both ptoct'ssing. but the lefr hcmisphere's rccognition pr:rforrnancc Fa;.: verbal and pictolial cngag*csboth hernispheres. tu codes) and did not. Patient \iP had simil:rr rcsults (t\liiler, Iiirrqstonc. and F; that these materiirls are remembered better than materials Gazzanie:r. 2002). F "pictulc that h:ne access ro single codes thc sr-rperioritv" S*,1 * etlict iPaivio and Cs:rpo, 197:i). *!'il \\ic coucluctccl a stLrclviCooncr,' et at., 2002) rvith a 3- split-brain Jratient usins :t simple full-liclcl, rrorrhtcralizcd F:.; *.. TFF. h E. WOLFORD. T,IILLL,R.A:'\D GAZZ.,\\IGA: SPLIT DECISIONS 1193 *€ F E. F ':E E-- * {- ;, + * to hequcncv f the sub.iects' guesses' Sub;ects colltinued collected separatcl'vftrr tl.reright of presentation \'vith responses Yellott stopped the match clluinq these last 5[-)tliiiis' \\ihen In tl-rrce separatc conditions' thr-. pzrtlent anci leli hancis. for their impressions' thev {iltes' experiment and asked subjects \'\'orclsjnamable objects, and uniamiliirr mcmorizecl thirt there rvas a fixccl Pattern patient o,re^ult,,lminglv responcled the presentation of each stin-rulusset' the l'oliolving and that the,v had frnallv ligured it tbr each to the iight sequences a rccognition memor) test with responses \\,asgive; to clescribc elaborate and complex lvhen the out. The,v proceeded har'ri. Consistent with dual-coding Predictions' right and le{i choices that resulted in their for namable objects sequences of subject used the right hand, memorv being correct' l'hese verbal reports-suPport ' - subject used the responses alr,vavs .o better than ltrr lvords, zrnd when the nu"i subjects had been searchine ficr fi-xed no bctter than the contention th:rt hand, memory for namable objects lvas ' left ancl were lboled into thinkinq they had picture superit''riw secluencesall along for faces. These lindings susgest that the contributi(ln of lelt and right suct'eeded. eftect results from the collectlve resuits from \\'e reasonecl that if frequency matching hemisphere brain regons during memorizetion' patterns even \'vhen there are none' and if the searching tbl --rrB:.',..;-i:'-*: by Gazzaniga is a left hernisphere intcrPreter postulated of the rvorld around LookingforPatterns neural str;cture thirt tries to make scnse relationship bt*ttl exis- it, then there n'right be an intimate , anc{ his colieagueshave long argarecltbr the 'Itl Gazzirniqa and the left hemisphere' test this referred to as the frequenc,v n.ratchine tence oi' a strllctLue rn the leli hemisphere rve latcralized the probabilit,v gttcssingparadigm'' \\'as the process that tricd tcr hypoth.sir, intclpr-ctct'. fhc intcrpreter field the stimuli to either the right or left visual of or ambiguor-rs information' p..r"rtti.tg meke sensc ollt of incomplete lrom split-brain patients :rnci coliecting the predictions -f illterprete r hzLsbeen cltmollstratcd trvo ir,: existcnct of sr"rchall that if appropnate contralateral hand' \!'e reasoned in rvhich the lelt hemisphere appar- the ,the JJ*.s-+:-''5i in scvctal c\pcrimcnts matching' then intcrpreter were resPonsible for frequency left . "I-elt" to explain rcsPonsesmacle b'v the ;i*...-. entlr' the neeci lelt hemisphere rve shoulci sce frecluencv matcliing with control of the right hcmisphere (Gazzaniea' hirnd r-rncler rvith right hemisphere for e'\rmin- presentation and nraximizing 2()00). \'\rc fecentlY developec{a new technique of the interprr:ter in the Presentalion. ing the existence and characteristics paradigm using That is what we founci' \Ve repiicated the \lilleq ancl Ga'zzan\ga' 2000)' l'he leli hemisphere ft\blford, rcasoning that patients with unilateral {iontal brain damage' simple and involves having the participant technique is quite darnage to the right u puti.rtt rvith unilatcral but r'videspread tu'o eventswill happen on the next trial' This gr.,.r, tuhi.h o1' the lelt hemisphere frontal cortex wolild perform similar to to as gr'ressing,was examilled fo.^.ligrrr, referred Probabilit-v a patient rvith uni- of a split-brain patient, ancl vicc versa for in the midclle of the twentieth cenlur)'' One ertensively hemisphere' As predicted' the tend t(' 1^,".o1 .lo*ogc to the left curious and easilv replicable finding is that hurnans Datientwithuni]ateralle|tfrontaldamagema-rimized,but match in this paradigm' Fiequencl matcl.rinq frequencv right frontal damasc frequency in tire pro- the patients with unilateral means that httmans tend to gltessthe alternatives shou's the clata averaged acrossthe two in the past So' mat;heci. Figure 85.3 portion at which they have been presented the patients rvitir ll'ontal lesions (see "left" "right," left occurs split-brain patients ancl if ,h. ,uuoalternatives are and and "le{t" individual graphs)' to guess original article lor on 709/0of the trials. participants "vill tend is curious about 70% of the tinrc' Frequenc\ matching from almost of tulf because it is nonoptimal and because animals Recognition (Hinson every other species rnaximize the optimal strateqv- have arzuecl that the concePt of self is always guessingthc most \rarious rcsearchers and ,Staclclon,1983). Nlaximizing and Klein is intimatelv relatecl to consciousness(Kihlstrom alternzr"tive. lrecl,rent aside the notion of con- that i997; Turk et a1.,in press). Leavilig likelv reason that httmans tiequencv match is l-he as portraved b'v Crick thev arc scior.rsnessduring visual perceptron believe there is a deterministic pattern' and thev anJ Koch, this voh'rme)'thc self as ' when told there isn't and Koch (seeCrick cieterminecl to find lhat pattern even t*P.1: ' seemsto be a major part of mlch (1969) pror"idecl a strikins demonstration that :rgent ::"t:t:"t one. Yellott rcailv dill rr-nr-from .r',,'". t, prot essitrq.,I^ a'u"""t " ''.rl'scll' lookillg lbr patterns iu these experimcnts' In his peopie \,vere there neurai cir- other lirrms of semanttc processine? t\re a stimullrs appeared either on tlie left ol' on the "*p..irrt.t-tt, processing? Could there be a light cuits specificall-vrelatecl to self or-teach tlial. and subjects had to predict u'hich ,ieht, hemisphere intcrpreter and the across .o.trt".tior-, benveen the left app.ar.'fhe probabiliq'of the lights r'vasvaried *o,-,ld finclings related to all three acttral pre- sel{? There have been interesting blocks. Subjects matched the lrequent--Yof the last fer'vvears' rvhen the fre- of these questions over thc sentatiolls (li'ccluencv matchins), changine lbllorving the lcvcl-ot--processrn9 of 50 trials' the light NIanv invcstisartors. qlrenc-v charrgccl. In tl-rc last block leads to ret..ardless tradition, have shorvn that self-relcvant Proccssing aopcarccl r,vhcrevcrthe subject Predictcd it rvor-rlcl' I 194 OONSCIOI]SNESS -n * -o.t 34s block time. Le{t hemi- :,.-l 1-rr ,.r.iph f,ri)r'e:clltstire plobabilitv of guessingthe gucssine the most lrequent stimuius 700,'hof the rieht hemi- r-i,'rt stirriulrL-.as a lttuctic.rttof henlisphere lbr t-ach block sphere presentaticins vielded lrequencv rnatching, but the most ::.11..l'he data are averageci over |lvo spLit-brain patlcnts sphere presentations viclded maximizing or guessine down by ,,rit'nt-r*'ith unilateral lrontal damage. The most lrcquent lrequcnt stimulus rnost of the tinie' i'fhe data. broken Gazzaniga' .::rlirrrLl ,0')o of thc tirne in all cases,and the horizontal individuals, are presented in \Volforcl, Nliller, and .. :r:itiri.,r o1' thc grzrph represents frequency matching or 2000.) fol- brt'.rf fLrl):('rllLt]nlnt{jllorv than el'en deep semantic pro- sphere was more apt to remember havine seen one's self in which the cc.sttrg :cc r('\'ic\\ ll Lockhart and Craik. 1990). Some lowing presentation of morphed photographs Of'neces- incstigatr.,r,.hnvc algrtccltirat selt:r'elevantprocessinq is trtrt self was pzrrtof the morph (Keenan et al., 2001). in a \VAD.\ qr-ralitativelv ciill'erent fi'om other lbrms rlf semantic pro- siry perceptic-rnand memorv are confounded is better in thc right ccs-.irrs Kihlstrom and I(1ein, 1997)' The,v argue that its paradiun.r. Gencrall,r: i'ace processing 1997), br-rt ach'antaqecrrmes 1i'om increased thnriliariw rvith self and the hemisphere (Kanr,visher.N'lcDermott, and Chun, studics bro:rcler arrav of associationsthzrt are availablc. Kelle,v and not necessarily processing of onc's olrn f'acc. Other for autobiographi- colleagues r'2()02)comParccl seif-relcvant processine to other- have shown a lefl hemisphere advantage face (Conlvav arid reler.'ant proce ssine anc[ to trpper- zrnd lowcrcase jndg;rnents' cal memory trnd for pictures of one's Tlier' lbund that both self-re1er,'antand other-relevant pro- Plevclell-Pearce,2000). (2002) examined cessingproducecl qreater activation in the leli ini'erior frontal In ur recent studv furk and colleagues a split-brain prrtient' cortex and in thc anterior tingulate lvhen compared to the perccptual recognition ol' sel{' in 'I'hev and one of three casejudrnrents, bltt there lv:rsno difference betrveen self and presented morphs of the patient of self' othcr in these regiorrs. Thc.v did find one are:l, the medial iamiliar others to the pzrtient. varvitls the Pcrcerltase of' morphs prelrontal cortex, in lvhich seil' processing r'vzrssullstantialh' in the morph. Thev rvcnt through each seqttence On some sequencesthe higher in activation level th:,rn eithel other or case Process- lrom 0% sell to 100% self twice. 'l:rken "yes" if he sar'r'himself. On ing. together, these findings slrggestthat self' proccss- patient was asked to respond a p;rrticular t-an'ril- ing is similar in some u':rvs brtt qu:rlitati','el,vdifferent in othcr- other sequences,he was askeciif he saw They lound a strong dissociation in that the patient wavs liottr decp rcnt:rltti(I)lr ).t :sillg. iar other. in right What about the pttssible rcl:rtionship between the left was more likely to identily the other firmiliar Person processine of self? The find- hemisphere presentations btrt substantiallv more likclv to hemisphere interpreter irncl the 'fhese ings lrom Kellev ancl colleae'Lres(2002) r'vere ambigtlous as irlentilr,' himself in 1eIi henrisphere Presentations. in the previotts to lateralitli and t1'renreclirl preliontal activation stracldled ciat:rclo not necessarilv resolve the ambigr-Lity left hernisphere mav the miclline. Given thc smoottlins alsoritiurs used, the acti- literature, but thcy do suggest that the 's not the case in the vation rnight have beelr bilirtcral or miqht have been later- be biased to perceive one self. Such r'vas alizecl to onc of' the two sidcs. The previous literature has right hcmisphere. spcak to the been mixccl lvittr respcct to thc laterality' of sclf processine' The fbregoingl data do not neccsszrrilv link between a Using \\ADA tests. Kceniilr zu'grteclthat the r-ight hemi- inr''olvcrnent o{' thc intcrpreter, but thc \,VOLFORD) MILLER) AND GAZZANIGA: SPLIT DECISIONS I I95 about the lzrmiliar other) rvhen the morph w'as pfe- strllctlrre th:rt trit's to rn:.rkesense of the rvtlricl and the per- asked to the lett hernispirere. but onlv 750/o of the time ception of sc1{'is con'rpelling. Both appcar to reside in the scnted and l5orb)rvhen the morph was prescnted to the right It:fi hcrnisphere. and a larse part o1' making sense ol tire iir0o,'o (lontinr-r- Thc averagc rate of ves responses across the rvorlcl seems ttt involve thoughts abotrt onc's sr'.Clf' hemisphere. morph liactions is presented in figure 85 4' ine in the speculative vein, it is possible that consciousncss, difl'erent .r\s the {ieure shorvs.presentations to tire Iett hemisphere the sclL and the lclt hemisphere intcrprcter are intimaielv more lil o o ao a C) l--+left hemisPhere o 0 6() 1- -+ - right hemisphere i o u o q. 30 4() so 60 70 ao 90 1()0 Percent self "fhe image. If thc patient t'rlrvayssaid vcs in both'ffi Frcunr 85.4 graph rcpresents the percentag-c of ves in thc rnorphccl the niczrsurer'vottld sum to 20f)0/oThe grapn !g responses summed over trials on which prticnt w:l's :rskcd to sav response.,,t,,-nti"s. are significantlv more conlrnon in the le{t' "ves" iI' he s:rw hinsell' ancl on tri:Llsin rvhich he ',vasaskec'l ttl sar" sbows that ves respolises "yes" if he san' it lumiliar othcr as a tr-rnctionoI percentage of self lrrnrirplrrr-. I 196 CONSCIOUSNESS \'\''eprcsr:nt a rouqh iclca of' this nrodel in thc cr,rntextr_rf Onr: of those probabilitv er,ressingparadiems vvzr"spartic_ a rectlgnition ntr'm(,r've.,ltr,rilir-nt rqquirine an olc.l/nelv uiarlv levealing In addition to exploring ner,, r.ariables.one respousc in rr.hich rhr- lr.st i-, pr.r:scntecito diflcrent hemi_ reason r,veke pt varvinq thc paradigm sphereson 5()nl(.sr:irrclui,:. was to keep our srrbjr:ct Thc Iirst stagelvorrlr.l be a deci- lrom the dcpths ol- boreclorrr.On one occasion wc srorr ab.Lrr rrirt'rrr,'r t() ll()tr1('r '1'rrc- useclfbcial t^,ing. snbjcct mig.ht hair as the event to preclict.So the split_brainpatient,J.\\1. dccic-lt:tllLt rlr,. rri.k \\1s roo clijllcult in the right 6emisphere was asked to preclict on each trial r,vhether the lace anci rr,rilrl i){)r i'elr t() tfy to clecide that rvhether the iterrr was rvould appear had thcial irair or nor. Ii)r the only time oid or 1,,,.' I ir,, .11];j5,g1lvc.,ulcl in onr make that dccision r,vithprob_ lengthy series,the patient frequenc,v matched lvith abiliri . i: tir,: sulrject thc right c:hosenot to try, thcn he or she r,vould hemisphere and responclccl ranclornlv r,vith the lelt rnak,- ., r:.,. r.i\Jr()nse that requi|ed hemi_ little thrtr_rghtor eI]brt. sphcrc. C)ur interpretatic,n w,asas above. F-aceswe re seen as S'i, 1,., r',.\:))nie rligi]t be pure uuessine(50/50),persevera_ the purview of' thc ,:i right irernisphcre. so onl,v that hemi_ rrr,r. .: .ir.glt.responscrancl so on. If thc snbjectchose to spliere took the task seriously ..,\ .rs rr.\ : l( in the left henrispher.e).thcn he n,ould asscss The asvmrnetries cliscr_rssed ,\l',11,i.t)t in this ancl in the prececline lir, i), the item on sonredirnensiorj ol.strejrlqth ancl sections hav,eimplications fbr tlte rt'spontl ',rld" natr-rreancl locatton oi.con_ il that strcnCth cxcceclccl:r criterion value ';r." -1 sciousness.Thcre arc undoubteclh. .rircl rrrlrr'r-rr specific modules in the 1.,'. ht' cltr.isi,rrrto bother trvrng wo'rcl Lre brain both 1br dilJlrerrt rlTresof processins i,lr.-r],rr ser.arl ancl ftrr clillbrent i.ir.l.r.:.Llr:lrlis the strengthiurcl qualit_v of rypes of stimr-rli.At least to some extent. these incliviclutrl i:r,' ln aii:ible infbr.rnation.rht. r.orrrexr. thc subjcct.sa priori rnoclulessecm to , ,lrt,(lerltr be relatuclto consciousrrpcriencc (Coonev in being able to pcrfirr-rntlre titsk.ancl so or.L. ancl ()azzaniga, 2003). T'ire Ir: moclular specificity of con- llro-s1stanclard rasks, it is difhcr,ritor irlpossible to clis- sciousnessis lurther indicatecl , ir'.,i]?l('thc by o*u..n.r, of. one,sdelicits tlvo proctesseswith the usual cl:rtaas collected. or the iack tl'rereol.lVith certain .\ rt,'r types of brain clamace. the i.ir,rrn.)t to trv in some conc_litionsof a stanclarcl recog_ patlent is fLrlly aware of problcms Ir_,ii,,l1rr;uclglrent and bothcred bv them. perracligrrwould shor,vup as :r reducecl \Vith other types ol- brain clarnage,therr: is iittle ri'lLrril :Lrrlijr,:r.ccl t:r.itrrion, or no aware- clepenclineon the cx:rct ol ncss. [pe A Irzrssag^clrom Sruss and Alexzrnder (2000) illustrates lorr-clliD.rrrsJ)()ns(, rh:rr thc sLrl;jectchose to use.The para- this specificity: "This domain sper:ifi<:itvis thc reason whr. dicrn ()i lir.k ancl cLrircirque-sr.v.s unusuar as it consistedof irnpaired clisorclersof awareness rr'hatcoulcl rvithin a specific nroclr_rle ltt clescrjlrrclas t\\.oscl)ariltc golno_eo tasks. one can exist. lbr exarnple, a lesion in jelt for each rcsp()nse the poster.ror rernpo_ olrrion. IJv uornbining-them, onc obtains rai lobe tvpicaliv rcsults in Wernicke,s all estil)tate,,l' aphasia (B"nson. th,'rr. illinqnr.\c l(, r.,ljotrd.r hr. lirst :ttgr,. 3pj 1979) . . . the patient is unaw.are in addition of the cornprehension an estirnate of the bias {br or zrsainstthe ,,se11.,, I-ailure or the abnormzrl speech. 11' danase response ln the oL-curs to the tlvo hemispheres once .t decision to try is right parietal iobe, the paticnt mav nesrect rnadc. Tb test the lert siclewith thc moclel st.stematic:allv,one would need to total un:rwarenessof' this neslect (Heilm:rn et rtrn a stand:Lrd rccosnitir)n al., l9B5).', !\,e or signal detection paracligm susgested earlier that 1br sorne tasks. a part of tl_re ancladd thc resl;olrseoption ,,don,t brain kno,"v',on cach trial. The assunles "don't that it is its job to handle that task. !\,e now knor.v" responses lvoulcl sussest bc exclr-rded{rom t}re esti_ that when that occur.s,that pzrrt of the blain is aiso lcspon_ marion of the traclitional sisnal detcction parameters. siblc lbr any awareness that accompanies Our sensefroni the task. lesting split-brain patients in a number of diverse paradigms is thlLt it secrns that in many cases ACKNow.r_EDcNrrNTs one Tl-ris rvork was suirported in part by NIH hernispheredcli:r.s to the other srant No. hen-risphcre.Thc rcsponses P5{)NS I r-778-19.Secrion S (i.iri anclNl.Nl.). !V,r: thank lront the unfavorc.cl Paul Corballis, hemisphcle look ranclon-rand vielcl low Nlars:rret-b'unncll. 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St:perabic routcs to hnrlan tlclnory iirrmation: Dissoci- cpisoclicnrlnl rr',.:l), .jili,rr i'rrri:siorrtornoq- r'irphl'finclings. f'lirc. atinq task and mateli:rl contributions in prefiontal corter. C)on. '. I )1 J. ,\'oll.,l;,:ti. \ 1|',1. r )I rr l(ll{ r. "\buro.;ti. Tr-inx. L). J..-1. L H:,.r:rrrr IVOLFORD. N{II,LI],R,AT\D GAZZANIGA: SPLIT Dts,CISIONS 1 199