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Predictive regularity representations and auditory streaming

IstvánWin�ler

3.4 Predictive regularity representations and auditory streaming

As�estate��before,theau��itor��strea�in���ara��i���(vanNoor��en1975;Fi��- ure3)hasbeenuse��extensivel��totestho�coherentsoun��sequencesarese��-re��ate��in�erce�tion.Theeffectsofsti�ulation�ara�etersonthe�erce�tual

or��anizatione�er��in��afterlistenin��toshorttonesequencesisoneofthe�ost

reliablefin��in��sofau��itor��sceneanal��sis(Fi��ure8).vanNoor��enfoun��three

��istinctareasinthefrequenc��-ratio/SOA�ara�eters�ace.Belo�the“Fission

boun��ar��”,�artici�antscoul���erceivethe��allo�in��rh��th�(inte��rate���erce�t),

butnott�o�arallelstrea�s.Abovethe“Te��oralcoherenceboun��ar��”,�artici-�antscoul��onl���erceivethesequenceinter�soft�ose�aratestrea�sofsoun��

(se��re��ate���erce�t).Bet�eenthet�oboun��aries,�artici�antscoul��voluntaril��

chooseoneortheother�erce�t(a�bi��uousarea).Thesefin��in��shavebeenta�- entoreflectthestren��thofthesu��ortforthet�oalternativesoun��or��aniza-tions�ithinthesecon���haseofau��itor��sceneanal��sis(Bre���an1990).When

thelar��e�ajorit��ofthe�ri�itiveheuristic�rocessessu��ortoneofthe�os-sibleor��anizations,theresultin���erce�tisfull����eter�ine��b��sti�ulus-��riven

(botto�-u�)�rocesses.When,ho�ever,su��ortfort�oor�orealternativesis

co��arabl��stron��,to�-��o�ninfluencescanti�thebalanceeither�a��.

Figure 8. Sche�aticillustrationoftheeffectsof�resentationratean��frequenc��ratio

intheau��itor��strea�in���ara��i���(seeFi��ure3).Seetextfor��etails.(A��a�te���ith

�er�issionfro�Denha�an��Win�ler2005.)

Anothera��arentl��reliablefin��in��isthat�artici�antsal�ostneverre�ort

�erceivin��se��re��ationatthebe��innin��ofthetonesequences.The�robabilit��of

these��re��ate���erce�tincreases��urin��thefirst5–15secon��softhesequence.

Thishasbeenter�e��thebuil��-u�ofau��itor��strea�in��(Bre���an1990).Neural

correlatesofstrea�buil��-u�havebeenobtaine��b��Sn����eran��hiscollea��ues

(2006).Ithasbeenassu�e��thatinitiall��,thebrainatte��tstointe��rateallinco�-

in��soun��intoasin��lestrea�.Strea�sareonl��se��re��ate���hensufficientevi- ��encehasbeen��athere��insu��ortofthe�resenceoft�oor�orese�aratecoher-entsequencesbein���ixe��to��etherintheau��itor��in�ut.Further�ore,it�asalso

assu�e��thatoncethebuil��-u��erio��isover,�erce�tionofthesoun��sequence

re�ainsconstant,atleastintheuna�bi��uousareasofthe�ara�eters�ace.

Ho�ever,fin��in��ssu��ortin��thebuil��-u�ofau��itor��strea�in���a��have

beeninfluence��b��the�etho��olo��icalas�ectsoftheex�eri�ents.Man��stu��ies

ofthis�heno�enonassu�e��that�artici�antscanonl��ex�eriencethesoun��se-quenceinter�sofoneoft�o��istinctor��anizations:eitherhearin��the��allo�in��

rh��th�or,in�arallel,alo�an��ahi��hre�eatin��soun��sequence,each�ithits

o�n�resentationrate.Asaconsequence,so�eofthestu��ies��i��not��istin��uish

bet�eenthelac�ofse��re��ationan��inte��rationorforce���artici�antstochoose

bet�eenthet�o�re-��efine���rece�ts,even�hentheiractual�erce�tion��i��not

�atcheitheroneofthe�.Ina�ilotstu����(re�orte��inDenha�etal.in�ress),

�artici�antsre�orte��anu�berof��ifferent�erce�ts��urin��lon��(4�inutes)au- ��itor��strea�in��sequences.So�eofthe�coul��becate��orize��asinte��rate��,be-causethe��inclu��e��are�eatin���atterninclu��in��bothlo�an��hi��htones;others

asse��re��ate��,becausethe��onl��inclu��e��re�eatin���atterns,se�aratel���a��eu�

ofeitheronl��lo�oronl��hi��htones;�ulti�lere�eatin���atterns,atleastoneof

�hich�asinte��rate��an��anotherse��re��ate��(“both”�erce�t);an��so�eti�es

�artici�antshear��nore�eatin���atternatall.Thustheassu��tionoft�o�utu-all��exclusive��istinct�erce�tsis�robabl��notvali��.Further�ore,recentstu��ies

foun��that,�hen�artici�antslistentolon��sequencesoftheau��itor��strea�in��

sti�ulus�ara��i���,�erce�tion��oesnotsettleonafinalstableor��anizationafter

thebuil��-u��erio��(Denha�etal.in�ress;Denha�&Win�ler2006;Pressnitzer

an��Hu�é2005,2006;Win�leretal.2005),notevenintheuna�bi��uousareasof

the�ara�eters�ace(Denha�etal.in�ress).Thusau��itor��strea�in��a��earsto

beabi-or�ulti-stable�heno�enon,si�ilarl��tothosefoun��invisual�erce�tion

(forrevie�s,seeBla�ean��Lo��othetis2002;Reesetal.2002),suchasbinocular

rivalr��(forarevie�,seeTon��etal.2006).

Denha�an��Win�ler(2005)for�ulate��ane�h���othesistoex�lainau��itor��

strea�se��re��ationan��,s�ecificall��,theresultsobtaine��intheau��itor��strea�-in���ara��i���.Wesu����este��thatau��itor��strea�in��canbe��escribe��inter�s

ofco��etitionbet�een�re��ictionsbase��ont�oor�orealternativere��ularit��

t�o�rinci�all����ifferentrules.Onerule�a�es�re��ictionaboutthesoun��i��e-��iatel��follo�in��thecurrentone:“Soun��“A”�illbefollo�e��b��soun��“B”an��

vice verse”.Another�ossiblerule�a�es�re��ictionstonon-a��jacentsoun��s:“Ev- er��secon��soun��is“A”,�hileever��otheris“B”.Itiseas��toseethatintheau��i-tor��strea�in���ara��i���,thefirstrulecorres�on��stotheinte��rate��,�hereasthe

secon��tothese��re��ate��soun��or��anization(seeFi��ure3).In��eneral,re��ularit��

re�resentationsarebase��onlin�sbet�eensoun��s�hichareuse��to�re��ict�hat

soun���illbeencountere��inthefuture.Follo�in��thechainof�re��ictionsfor

a��ivenre��ularit��createsacoherent(re��ular)soun��strea�.Theh���othesis�ut

for�ar��b��Denha�an��Win�ler(2005)isthatau��itor��strea�sarebase��on

suchre��ularit��re�resentations.Further�ore,�eassu�ethatre��ularities�rovi��-in����ifferent�re��ictions(for�in����ifferent��irecte��lin�s)areinco��atible�ith

eachotheran��thusviefor��o�inance.Co��etitioncontinuesaslon��asinco�-�atiblere��ularit��re�resentationsexistinthebrain.Theor��anizationbase��onthe

�o�entaril��stron��ersetofre��ularitiesa��earsin�erce�tion.

Thestren��thofalin�bet�eent�osoun��sis��eter�ine��b��thete��oral

an��s�atialoverla�bet�eenthesti�ulusafter-effectsinthebrain.Thatis,��iven

the�ell-�no�ntonoto�icor��anizationin�an���artsoftheau��itor��s��ste�,

t�otonesclosetoeachotherinfrequenc���illactivate�oreneuronsinco�-�onthant�otones�orese�arate��infrequenc��.Further�ore,�henasoun��

follo�sanother�ithinashort�erio��ofti�e,itencountersstron��erlin��erin��

effectofthe�revioussoun��thanifitfollo�e��theothersoun��afteralon��er

ti�e.Thesean��si�ilarsi��le�rinci�les��overnho�fasta��ivenre��ularit��can

be��iscovere��b��thebrainan��ho�stron��thelin�sbet�eensoun��s(there��u-larit��re�resentation)is.Man��ofthe��rou�in���rinci�lesinitiall����escribe��b��

researchersoftheGestaltschoolof�s��cholo����(see,e.��.,Köhler1947)canbe

easil��translate��intothelan��ua��eofthenervouss��ste�this�a��.

Insu��ortoftheabove��escri�tionofau��itor��strea�in��,Denha�etal.(in

�ress)foun��intheau��itor��strea�in���ara��i���that�ithver��fast�resentation

ratesan��lar��efrequenc��se�arationbet�eenthet�otones,se��re��ationoften

e�er��esasthefirstre�orte���erce�t.Thatis,nobuil��-u�canbeobserve��.The

co��etitionbet�eenre��ularit��re�resentationsh���othesis�rovi��esanex�lana-tiontothis�heno�enon.Whenthefrequenc��se�arationbet�eenthet�otones

islar��e,thereislittleoverla�bet�eentheirneuralafter-effects.Thusintheau��i-tor��strea�in��tonesequence,lin�sbet�eena��jacentsoun��s�illbe�ea�an��

ta�elon��erti�etobuil��.Lin�sbet�eeni��enticaltonesarenot��e�en��enton

thefrequenc��se�arationbet�eenthet�otones.Ho�ever,buil��in��theselin�s

isver��sensitivetotheintervalse�aratin��successivei��enticaltones.Withafast

�resentationrate,theti�ese�aratin��successivei��enticaltonesisshort.Thusthe

re��ularitiesbase��onlin�sbet�eeni��enticaltones�illbestron��an��canbe��is- covere��fast.Theset�oeffectsto��etherex�lain,�h��se��re��ation(theor��aniza-tionbase��onlin�sbet�eeni��enticaltones)a��earsasthefirst�erce�tinan

au��itor��strea�in��sequence�resente��atahi��hratean��havin��lar��efrequenc��

se�arationbet�eenthet�otones.

Another �iece of evi��ence su��ortin�� the co��etition bet�een re��ularit��

re�resentationsh���othesisco�esfro�observin��therateofs�itchin��bet�een

inte��rate��an��se��re��ate��re�resentationsasafunctionofthesti�ulation�ara�-eters.Tra��itional��escri�tionsofau��itor��strea�in��assu�ethatnoorver��s�all

a�ount of s�itchin�� shoul�� occur in the una�bi��uous areas of the �ara�eter

s�ace.S�itchin���a��be�resentinthea�bi��uousarea.Incontrast,there��ularit��

co��etitionh���othesissu����eststhat�osts�itchin��shoul��occur�henbothre��-ularit��re�resentationsarestron��.Thatis,�osts�itchin��shoul��occur�henthe

frequenc��se�arationbet�eenthetonesiss�all(stren��thenin��thelin�sbet�een

a��jacenttones;theinte��rate���erce�t)an��the�resentationrateishi��h(stren��th-enin��thelin�sbet�eeni��enticaltones;these��re��ate���erce�t).Althou��h�artof

this�ara�eterran��efallsintothea�bi��uousarea,(1)italsoexten��stouna�-bi��uousareas(seeFi��ure8)an��(2)alar��e�artofthea�bi��uousareahaslo�

to�e��iu�frequenc��se�arationan���e��iu�toslo��resentationrates.It�as

foun��(Denha�etal.in�ress)thatthehi��hestrateofs�itchin��fallsexactl��tothe

area�re��icte��b��there��ularit��co��etitionh���othesis,�hereasthea�ountof

s�itchin��inalar��e�artofthea�bi��uousareais�uchlo�er(seeFi��ure9).

Theinter�retationofDenha�etal.’s(2005,in�ress)resultssu����eststhatthe

au��itor��s��ste�for�sseveralre��ularit��re�resentationsforthesa�esoun��se-quencein�arallel.The��alsoar��uethatthere��ularit��re�resentations�ust�rovi��e

�re��ictionsaboutsoun��soccurrin��laterinthesequence.Can�ethenfin��si��ns

ofthat(a)soun��sequencesare��escribe��in�arallelb���ulti�lere��ularit��re�re-sentationsinthebrainan��(b)re��ularit��re�resentationsare�re��ictive?Astothe

firstquestion,Horváthan��collea��ues(2001)sho�e��thatre�resentationsforthe

t�ore��ularities��escribe��abovefortonealternation(lin�sbet�eena��jacentan��

lin�sbet�eeni��enticaltones)areactivein�arallelinthehu�anau��itor��s��ste�.

Theseauthorssho�e��thatviolatin��eitheroneofthet�ore��ularities(�ithout

violatin��theotherone)elicitstheMMNres�onse.Severalstu��iesfoun��results

co��atible�iththe�re��ictivenatureofthere��ularit��re�resentationun��erl��in��

theMMNres�onse(Horváthetal.2001;Paavilainenetal.2007;Tervanie�iet

al.1994aan��b).The�ostconvincin��evi��ence�asobtaine��b��Paavilainenan��

collea��ues(2007)�hosho�e��thatMMNiselicite��b��occasionall��violatin��a

�re��ictionbet�eena��jacentsoun��s.Sequences�ereconstructe��fro�shortlo�,

shorthi��h,lon��lo�,an��lon��hi��htones.Shorttones�ereusuall��follo�e��b��

lo�,lon��onesb��hi��htones.Theshort-lon��attribute�asvarie��ran��o�l���ith

equal�robabilities.Occasionalhi��htonesfollo�in��shorttonesan��lo�tonesfol-lo�in��lon��toneselicite��theMMNres�onse.Becauseinthis�ara��i���,MMN

coul��onl��beelicite��iflo�tonesbeca�eex�ecte��follo�in��ashorttonean��

hi��htonesafteralon��tone,Paavilainenetal.’sresults(sincethenre�licate��b��

Ben��ixenetal.2008)stron��l��ar��uefor�re��ictionsbein����enerate��onthebasis

ofthere��ularit��re�resentationsinvolve��inMMN��eneration.Recentl��,��irect

ERPevi��enceofthe�re��ictivenatureofau��itor��re��ularit��re�resentationshas

beenobtaine��b��Ben��ixenan��collea��ues(2009).

Inthissection,�esu����este��a��escri�tionofau��itor��strea�in��inter�sof

co��etitionbet�eenre��ularit��re�resentations�ro��ucin��inco��atible�re��ic- tions.Evi��encefavorin��thish���othesisoverthetra��itional��escri�tionofau��i- tor��strea�in��hasbeenrevie�e��.Finall��,�esho�e��thattheco��etin��re��u-larit��re�resentationsare�aintaine��in�arallelintheau��itor��s��ste�an��that

�re��ictionsbase��onthesere��ularit��re�resentationsareutilize��b��theau��itor��

��eviance��etection�rocessin��exe��b��theMMNres�onse.

Figure 9. Grou�-�ean��istributionof�erce�tuals�itchin��asafunctionoffrequenc��

se�aration(��finse�itones)an��thesti�ulusonsetas��nchron��(SOAin�illisecon��s).

The��re��scalein��icatesthe�eannu�berofs�itchesacross�artici�antsaccu�ulate��

throu��houtthetonetrains,se�aratel��foreachco�binationof�ara�eters.Notethatthe

surfaceisinter�olate��bet�eenthe��iscreteex�eri�ental��ata�ointsin��icate��b��the

s�alle��t��circles.Thete��oralcoherencean��thefissionboun��ar��are�ar�e��b��

��ashe��lines.