Predictive Feedback and Conscious Visual Experience.

1 MB·English

by  Panichello, Matthew F.

REVIEWARTICLE
published:21January2013
doi:10.3389/fpsyg.2012.00620
Predictive feedback and conscious visual experience

MatthewF.Panichello1*,OliviaS.Cheung1 andMosheBar1,2

1AthinoulaA.MartinosCenterforBiomedicalImaging,MassachusettsGeneralHospitalandHarvardMedicalSchool,Charlestown,MA,USA
2GondaMultidisciplinaryBrainResearchCenter,Bar-IlanUniversity,Ramat-Gan,Israel

Editedby: The human brain continuously generates predictions about the environment based on
LarsMuckli,UniversityofGlasgow, learned regularities in the world.These predictions actively and efficiently facilitate the
UK
interpretation of incoming sensory information.We review evidence that, as a result of
Reviewedby:
this facilitation, predictions directly influence conscious experience. Specifically, we pro-
AnilK.Seth,UniversityofSussex,UK
EdwardVul,MassachusettsInstitute posethatpredictionsenablerapidgenerationofconsciousperceptsandbiasthecontents
ofTechnology,USA ofawarenessinsituationsofuncertainty.Thepossibleneuralmechanismsunderlyingthis

RobertD.Gordon,NorthDakotaState facilitationarediscussed.

University,USA
*Correspondence: Keywords:predictions,context,objectrecognition,priming,visualawareness,top-down,perception,associative
MatthewF.Panichello,Martinos processing
CenterforBiomedicalImaging,149
ThirteenthStreet,Suite2301,
Charlestown,MA02129,USA.

e-mail:[email protected].

harvard.edu

INTRODUCTION and with less interference by sensory noise. In other words,the

Perceptionhasevolvedtotransformrawsensorysignalsintoinfor- expectation elicited by a yellow traffic light may cause a driver

mation that can guide behavior. But perception is not a purely to consciously perceive the subsequent red light more quickly

stimulus-driven phenomenon; the brain perceives the world than otherwise possible. We conclude by discussing the neural

proactively. Endogenous influences, such as attention, memory, mechanismsunderlyingthesepredictiveinfluences.

andmood,guideperceptiontoensurethatinformativerepresen-

tationsoftheenvironmentaregeneratedasefficientlyaspossible. PREDICTIONSINFLUENCECONSCIOUSPERCEPTION

In this review, we focus on the influence of predictions on PREDICTIONSGUIDETHEINTERPRETATIONOFAMBIGUOUSSTIMULI
visualperception.Thepredictionswediscussarenotanalogousto Onemethodforstudyingtheinfluenceofpredictionsonaware-
the deliberate,elaborative foresight that individuals may engage nessistoshowobserversstimuliwithmultipleperceptualinter-
inwhenplanningforthefuture(e.g.,thinkingaboutwhichroute pretationsanddetermineifpredictionsaffectwhattheysee.The
homefromworkwillhavetheleasttraffic).Instead,weusetheterm popularperceptualphenomenonknownasbinocularrivalrypro-
“prediction” here to refer to expectations about the immediate vides a convenient means to accomplish this. Binocular rivalry
sensory environment based on previous experience and learn- occurswhenauniqueimageispresentedtoeacheye;interpreta-
ing.Througheverydayexperience,individualslearnmanytypes tionofthestimuliisinherentlyambiguousbecausethetwoeyes
of regularitiesintheworld,suchasassociationsamongitemsor provideconflictinginformationaboutthesharedportionof the
events.Forexample,ayellowtrafficlightisalmostalwaysfollowed visualfield.Thebrainmustworkoutthemostlikelyinterpreta-
byaredlight.Insofarastheenvironmentisgenerallyregular,it tionofthisimpossibleinput(Hohwyetal.,2008).Theresolution
is,toanextent,predictable.Expectationsabouttheenvironment of this problem is striking:the two stimuli do not fuse together
canbederivedfromtheselearnedregularitiesandusedtoguide intoablendedpercept,butratheralternatelydominateperception
sensoryprocessing,presumablyviatop-down(descending)pro- (forreviewsofbinocularrivalryandmultistableperceptionmore
jectionslinkingbrainregionsinvolvedingeneratingexpectations generally,seeLeopoldandLogothetis,1999;BlakeandLogothetis,
withlower-levelsensoryregions. 2002;Sterzeretal.,2009).
If predictions guide processing in visual areas,it follows that Binocular rivalry is sensitive to many factors,including low-
thisfacilitationmayhaveconsequencesforconsciousperception1. level stimulus properties (e.g., Kaplan and Metlay, 1964; Fahle,
Wearguethatpredictivemechanismsmayshapethecontentsof 1982)andhigher-orderendogenousinfluencessuchasattention,
visual awareness during instances of sensory ambiguity, allow- imagery,andaffect(e.g.,OoiandHe,1999;Pearsonetal.,2008;
ing subjective experience of the world to remain informative Andersonetal.,2011),soasingleprocessormechanismshould
and coherent. Additionally, when sensory input is less ambigu- not be credited as the“source”of rivalry (Blake and Logothetis,
ous,predictionsmayallowperceptstobegeneratedmorequickly 2002). However, recent findings suggest that predictions play a
roleinresolvingtheambiguityinherentinthisphenomenon.For
1Weuse“subjectivevisualexperience,”“consciousperception,”and“visualaware- example,a stimulus will tend to dominate rivalry if it has been
ness”interchangeablytorefertothephenomenologicalexperienceofseeing,distinct presented more frequently than the competing stimulus in the
fromotherformsofconsciousnesssuchasself-awareness. recentpast;thelikelihoodofeachstimulusisestimatedbasedon
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Panichelloetal. Predictionsandconsciousperception
recentexperience,generatingexpectationsthatcanguidepercep- Bistable figures have two mutually exclusive interpretations that
tion(ChopinandMamassian,2012).Thetendencyofstimulito alternatelydominateawarenessduringviewing.However,apre-
change position smoothly during motion can also provide pre- dictivecuerelatedtooneoftheinterpretationsofabistablefigure
dictive cues for perception. Thus, observers who view a stream can bias perception in favor of that interpretation (Figure 2A;
ofimagesdepictingarotatinggratingaremorelikelytoperceive BugelskiandAlampay,1961;BalcetisandDale,2007;Goolkasian
the stimulus consistent with the rotation trajectory at the onset andWoodberry,2010).Stimulicanalsodisplaybistablemotion;
of rivalry (Figure 1A; Denison et al., 2011). Verbal stimuli can anarrayofmovingdotstimulicanbearrangedsothatobservers
also produce an expectation for semantically related stimuli. To perceive a rotating cylinder with spontaneous reversals in rota-
demonstratethis,Costelloetal.(2009)usedavariantofbinocular tion direction. However, when observers are led to expect that
rivalry,termedcontinuousflashsuppression,whichreliesonthe thecylinderwillconsistentlyrotateinaparticulardirection,this
tendencyofhigh-contrastdynamicnoisetodominateawareness interpretationdominatesperception(Sterzeretal.,2008).
when presented in rivalry with another stimulus (Tsuchiya and Intriguingly,predictionscanaltertheperceptionofstimulithat
Koch,2005).Costelloetal.foundthatawordpresentedtooneeye are normally perceptually stable. For example,most individuals
breakssuppressionbyhighfrequencynoisepresentedtotheother see the left disk in Figure 2B as a convex and the right disk as
eyemorequicklywhenasemanticallyrelatedprimeisdisplayed concave. However,the contour of each disk is actually ambigu-
priortorivalry(Figure1B). ous:thissubjectiveinterpretationisdrivenbytheshadingofthe
Inadditiontobinocularrivalry,bistablefiguresrevealtheabil- figuresandthelearnedassumptionthat“lightcomesfromabove”
ity of top-down predictions to influence conscious perception. (Brewster,1826;SunandPerona,1998;Adamsetal.,2004).New
experiencecontradictingthisassumptioncancauseasubstantial

FIGURE1|Predictionsaffecttheoutcomeofbinocularrivalry.(A)
Whenastreamofimagesdepictingagratingrotatingin45˚incrementsis FIGURE2|Predictionsaffecttheinterpretationofambiguousstimuli.
presentedtobotheyes,observersaremorelikelytoperceivethegrating (A)Exampleofanambiguousfigurewithitstwopossibleperceptual

consistentwiththispattern(the“matchingeye”stimulus)attheonsetof interpretationsemphasized(left).Viewingaprimerelatedtooneofthe
rivalry.Adapted,undercreativecommonslicense,fromDenisonetal. interpretations(right)biasesperceptioninfavorofthatinterpretation.
(2011).(B)Awordprime(“salt”)causesasemanticallyrelatedtargetword Adapted,withpermission,fromGoolkasianandWoodberry(2010).
(“pepper”;lefteye)tobreaksuppressionbydynamicnoise(righteye) Copyright©bySpringerPublishing.(B)Thesetwodisksappeartobe
duringrivalrymorequicklythanwhentheprimeandtargetarenotrelated. concaveandconvex,respectively,duetolearnedassumptionthatlight
Theincreasingcontrastofthetargetovertimehelpsensurethatthetarget comesfromabove.Experienceviolatingthisassumptioncausesanew

eventuallybreakssuppression.Adapted,withpermission,fromCostello shadingschemetomaximallyevoketheillusionofcontour.Adaptedfrom
etal.(2009). Adamsetal.(2004).Copyright©byNaturePublishingGroup.

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Panichelloetal. Predictionsandconsciousperception
shiftininferredlightposition;asaresult,anewshadingscheme “contextframes”(Friedman,1979).Cueswithinascenecanacti-
willmaximallyevoketheillusionofcontour(Adamsetal.,2004). vateassociatedcontextframes,allowingobserverstopredictother
Similarly,individualslearnovertimethatfast-movingobjectsare features of the environment (Bar, 2004). Accordingly, observers
lesscommonthanslowmovingandstationaryobjects,producing identifyobjectsfasterandmoreaccuratelywhentheyareshown
anexpectationthatcanguideperception.Newvisualexperience in their typical environment (e.g., a toaster in the kitchen, Bie-
dominatedbyfast-movingstimulialtersthisexpectation,andby derman,1972; Palmer,1975; Biederman et al.,1982; Davenport
extension,subsequentmotionperception(StockerandSimoncelli, and Potter,2004) or are preceded by an object drawn from the
2006; Sotiropoulos et al.,2011). Together,these studies demon- samecontext(e.g.,abedroomdresserandavanitymirror,Gronau
strate that predictions derived from experience can affect how etal.,2008;seealsoSachsetal.,2011).Conversely,recognitionis
observersseetheworld. impairedwhentheexpectedspatialrelationshipsamongobjects
inascenearedisrupted(Biederman,1972).
PREDICTIONSFACILITATEPERCEPTIONDURINGOBJECTRECOGNITION Associations among stimuli can be reinforced over a lifetime
Evenwhenvisualinputisnotambiguous,predictivemechanisms ofexperience.However,theycanalsobegeneratedquitequickly
mayinfluenceconsciousperception.Wehypothesizethatpredic- underartificialconditionsinthelaboratory(e.g.,ChunandJiang,
tions allow conscious percepts to be generated more efficiently 1998,1999;Aminoffetal.,2007;Kimetal.,2009;denOudenetal.,
and with less inhibition by sensory noise2. The most direct evi- 2010;Turk-Browneetal.,2010).Thus,associativelearningappears
denceforthisclaimisprovidedbystudiesshowingthatpredictions tobequiteflexibleandcontinuouslyupdated.Forinstance,ina
can facilitate perception of objects when visual input is noisy. studyofperceptualprediction(denOudenetal.,2010),observers
Observers viewing fragmented object figures are more likely to were asked to judge whether a degraded image depicted a face
perceive the objects when they are informed about their cate- or a house. An auditory cue presented at the start of each trial
gory(e.g.,“ananimal”foranelephant;Reynolds,1985).Similarly, signaledwhichstimulustypewasmorelikelytoappear,andthe
observersinstructedtoindicatetheirsubjectivevisualexperience experimentersmanipulatedthepredictivestrengthof thesecues
report successfully perceiving expected stimuli at greater levels over time. Modeling of the behavioral data demonstrated that
of degradation or lower contrast than unexpected stimuli (Eger observersupdatedtheirestimatesofstimuluscategorylikelihood
etal.,2007;EstermanandYantis,2010;Mellonietal.,2011).Inthe on a trial-by-trial basis and responded more quickly when cues
latterstudy,electrophysiologicalactivityevokedbyexpectedstim- werehighlypredictive.
ulicorrelatedwithsubjectiveexperienceearlierthanthatevoked Apart from learned associations among stimuli, preliminary
by unexpected stimuli, suggesting that predictions reduced the processingofvisualinformationcanalsocreateexpectanciesthat
latencyofneuralactivityrelatedtoconsciousperception(Melloni facilitate perception.Visual stimuli contain information distrib-
etal.,2011). utedacrossarangeofspatialfrequencies(Figure3A).Lowspatial
Alargebodyof researchdemonstratesthatpredictionsmake frequency(LSF)informationisrapidlyextractedfromincoming
objectrecognitionfasterandmoreaccurate.Thesestudiesprovide sensoryinputandencodesgrosspropertiessuchastheglobalshape
additional,althoughindirect,evidenceforpredictivefacilitationof oftheenvironmentanditsconstituentobjects(Figure3B).Incon-
consciousperception.Theseresultsmustbeinterpretedwithcau- trast,highspatialfrequency(HSF)informationisprocessedmore
tion for two reasons. First, object recognition is a multifaceted slowlyandcorrespondstoedgesandfinedetails(Figure3C;Shap-
process,withmultiplestagesthatmaybeamenabletoinfluenceby ley,1990;SchynsandOliva,1994;Baretal.,2006).Itispossible
predictivemechanisms(e.g.,theassignmentofsemanticattributes that LSF information can elicit predictions (Bar, 2003) because
totheperceivedobject).Second,mostofthestudiescitedbelow objects in the same basic-level category often display a similar
examined the influence of predictions on behavioral proxies of global shape (Rosch et al., 1976). For example, individual dogs
recognition such as reaction time rather than subjective reports varytremendously,butalldogsshareroughlythesamegrossfea-
ofperception.However,itwillbeworthwhileforfutureresearch tures (e.g.,four legs and a tail),which immediately differentiate
todetermineifpredictivefacilitationofobjectrecognitionisdue, them from members of many other basic-level categories. With
atleastinpart,tofasterandmoreaccurategenerationof object experience,wecometolearnthedefiningfeaturesofmanykinds
percepts. ofobjects.Thus,whileLSFinformationlacksfinedetail,itissuf-
Forinstance,contextualfacilitationofobjectrecognitionarises ficienttotriggergeneralcategoryinformationstoredinmemory
from the knowledge that certain objects often reliably co-occur that guides interpretation of the stimulus (Bar,2003; Bar et al.,
inparticularsettings.Cubiclesandcopymachines,butnotocto- 2006;OlivaandTorralba,2007).Inadditiontoindividualobjects,
puses and cars, are found inside office buildings. Furthermore, differentexemplarsofbasic-levelscenes(suchasacitystreet)also
objectswithinacontextareoftenarrangedinaregularmanner: shareglobalfeaturesthatcanconstrainandfacilitaterecognition
computer monitors rest on desks inside of cubicles. Over time, (Bar,2004;OlivaandTorralba,2007).Thus,rapidprocessingof
observerslearnmanysetsofsuchregularities,termedschemataor LSFinformationmayexplaintheremarkableabilityofobservers
toextractthe“gist”ofasceneataglance(Biedermanetal.,1974;
Thorpeetal.,1996;OlivaandTorralba,2007).
2When interpreting the influence of predictions on perception,it is important Tosummarize,predictionsmayshapethecontentsofawareness
to consider potential contributions of attention because the two may be easily
whenvisualinputisambiguousandenablefasterandmoresen-
confounded. However, attention and prediction are dissociable in several ways
(Hohwy,2012;SummerfieldandEgner,2009)andeffortshavebeguntoelucidate sitive conscious perception under less strenuous circumstances.
theindependentcontributionsofeachtoperception(Wyartetal.,2012). The ability of predictions to shape perception under conditions
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Panichelloetal. Predictionsandconsciousperception

FIGURE3|Animagefilteredtoinclude(A)bothlowandhighspatialfrequencyinformation(B)predominantlylowspatialfrequencies

(C)predominantlyhighspatialfrequencies.Thelowspatialfrequencyinformationin(B)isnotsufficienttoidentifythepolarbearbutnevertheless

substantiallyconstrainsthepossibleinterpretationsofthestimulus.

of uncertainty is clearly advantageous; it is better to generate a Thispredictivecodingframeworkhastraditionallybeenpre-

meaningful interpretation of the world, informed by previous sentedwiththehierarchicalorganizationofsensorycortexinmind

experience, than to faithfully represent a noisy sensory signal. (e.g., Mumford, 1992; Friston, 2005). However, the existence of

When visual input is more informative, predictions still guide reciprocal connections between prefrontal and visual cortices in

sensory processing to make conscious perception as efficient as themacaque (Websteretal.,1994;Cavadaetal.,2000)andevi-

possible.Notethatalthoughwesuggestthatpredictionsinfluence dence of functional interaction between prefrontal and inferior

consciousexperience,predictionsthemselvesmaybelearnedand temporalregionsinhumans(e.g.,Baretal.,2006;Kveragaetal.,

appliedwithoutawareness(e.g.,ChunandJiang,1998,1999;Kim 2007;Axmacheretal.,2008)arewelldocumented.Thesefindings

etal.,2009;Turk-Browneetal.,2010).Wenextconsiderhow,at suggest that prefrontal regions provide an additional source of

theneurallevel,predictionsmayguideperception. feedbacktothevisualhierarchy(butnotethatprefrontalregions

do not seem to be arranged hierarchically with respect to each

THENEURALBASISOFPREDICTION other;Yeoetal.,2011).Accordingly,expectation-basedprefrontal

DESCENDINGCORTICO–CORTICOPROJECTIONSALLOWPREDICTIONS modulation of sensory processing has been reported (Bar et al.,
TOGUIDESENSORYPROCESSING 2006; Summerfield et al., 2006; Eger et al., 2007; Kveraga et al.,
An increasingly popular framework (e.g., Mumford, 1992; Rao 2007;Gamondetal.,2011).Predictivemechanismsmaythusbe
andBallard,1999;Friston,2005;FristonandKiebel,2009),termed instantiatedinavarietyofbrainregions,butconsistentlyseemto
“predictivecoding”,positsthattop-downpredictionsfacilitateper- dependontheuseofdescendingconnectionstoallowthedynamic
ceptionbyreducingtheneedtoreconstructtheenvironmentvia comparisonofpredictionswithsensoryinput.
exhaustivebottom-upanalysisofincomingsensoryinformation. Converging imaging and computational evidence supports
Validatedpredictionsefficientlyexplainawaysomeofthesensory the proposed role of predictive feedback during perception. If
input, conserving resources for analysis of unpredicted compo- descending predictions efficiently facilitate the interpretation of
nents. The hierarchical organization of sensory cortex suggests sensory input, then predicted stimuli should evoke less activity
a natural computational architecture for the integration of top- insensorycortex,consistentwiththenotionthatstimulus-driven
downpredictionsandbottom-upsensoryinformation.Ascending activityconveysan“errorterm”communicatingtheremainderof
projectionsinsensorycortexaresparseandfocused,terminating thesignalthathasnotbeenexplainedbytop-downpredictions.
in predominately layer 4 of cortical targets,whereas descending Thiseffectshouldbeespeciallypronouncedinvisualprocessing
connections project to a larger number of region and innervate regionsthatareparticularlydevotedtotheprocessingofthepre-
their targets in superficial and deep layers of cortex (Felleman dicted stimuli. Accordingly, shapes that appear in an expected
andVan Essen,1991;Friston,2009). Predictive coding proposes location in the visual field elicit less activity in the retinotopic
thatdescendingprojectionsconveypredictionsaboutthecontent regionV1(Alinketal.,2010),andexpectedfaceandplacestimuli
ororganizationofthesensoryinput.Ascendingprojectionscon- elicitlessactivityinfaceandplace-sensitiveregionsofhigh-level
vey any information incongruent with the predictions (i.e., an visualcortex(Egneretal.,2010).
“errorterm”)receivedfromhighersensoryareas.Thus,recipro- Moreover,becausepredictivefeedbackfromhigher-levelpro-
cally connected cortical areas are able to engage in a dynamic cessingregionsshapestheactivityoflower-levelsensoryregions,
process in which predictions are modified based on incoming activity in lower-level sensory regions should track surprisingly
sensory input until the higher-level region is able to arrive at sophisticated aspects of the sensory input. A subset of retino-
reasonableapproximationoftheincominginput(Ullman,1995; topic neurons in visual cortex seem sensitive to stimuli outside
Friston,2005). oftheirreceptivefields,apropertyreplicatedinacomputational
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Panichelloetal. Predictionsandconsciousperception
model of visual cortex allowing for predictive feedback to these
cells(RaoandBallard,1999).Similarly,activityinlow-levelretino-
topicvisualareasvarieswithimagerecognition(Hsiehetal.,2010;
seealsoGorlinetal.,2012),consciousexperienceoffigure-ground
segregation(Lammeetal.,1998,2002),andtargetdetection(Supèr
et al.,2001),implicating top-down modulation by higher-order
areas.
Tosummarize,expectationsderivedfromlearnedregularities
are able to guide perception via descending feedback targeting
sensory regions. We next elaborate on these ideas by reviewing
the neural mechanisms for two previously discussed predictive
processes:predictionsbasedoncontextualassociationsandpre-
dictions based on preliminary LSF information extracted from
stimuli. Different neural generators may support these mecha-
FIGURE4|Thecontextnetwork.Acontrastofstrongandweakcontext
nisms, but evidence suggests that both may require interaction
objectstimuli,revealingthecontextnetworkonthelefthemisphereofan
betweenhighercorticalareasandvisualcortextoallowtop-down inflatedcorticalsurface.RSC,retrosplenialcomplex;PHC,parahippocampal
predictionstoshapesensoryprocessing. cortex;MPFC,medialprefrontalcortex.ReprintedfromKveragaetal.
(2011).Copyright©byNationalAcademyofSciences/HighwirePress.
PREDICTIONSBASEDONCONTEXTUALASSOCIATIONSAMONG
OBJECTS
In the previous section,we have suggested that contextual asso- Malachetal.,1995;Grill-Spectoretal.,2001).Contextualinfor-
ciations among objects can create expectancies that guide per- mation modulates LOC response during recognition (Altmann
ception.Adistributednetworkincludingparahippocampalcortex etal.,2004;Gronauetal.,2008;MacEvoyandEpstein,2011),sug-
(PHC),retrosplenialcomplex(RSC),andmedialprefrontalcor- gesting that this region may be receiving feedback signals from
tex(mPFC)mediatesthesecontextualassociations(Figure4;Bar contextualprocessingregions.Furtherresearchwillneedtoclar-
andAminoff,2003;Kveragaetal.,2011).Tolocalizethiscontext ifythepreciseneuralmechanismbywhichcontextualpredictions
network, activity elicited by objects that are strongly associated guideprocessinginsensorycortex.
withaparticularcontextiscomparedwiththatelicitedbyobjects
that are only weakly associated with any particular context. For PREDICTIONSBASEDONLOWSPATIALFREQUENCYINFORMATION
example, golf carts are usually found in the context of a golf Theprefrontalcortex,specificallyorbitofrontalcortex(OFC),may
course and are thus closely associated with other objects that playacriticalroleingeneratingpredictionsbasedonLSFinfor-
share this context such as golf clubs and golf balls, while cam- mation(Bar,2003;Baretal.,2006).Inthisproposedframework,
eraslackstrongassociationsbecausetheyarefoundinavariety LSFinformationisextractedfromvisualinputandprojectedto
of contexts and thus do not consistently appear with any par- OFCviathemagnocellularcellsofthedorsalvisualstream,which
ticular set of objects (Bar and Aminoff, 2003; stimuli available preferentially respond to and rapidly conduct LSF information
at http://barlab.mgh.harvard.edu/ContextLocalizer.htm). Thus, (Maunselletal.,1990;Shapley,1990;MeriganandMaunsell,1993;
associative processing seems to specifically engage these context BullierandNowak,1995;Chenetal.,2007).Aswehavesuggested,
networkregions.Furthersupportforthisclaimisprovidedbythe thecoarserepresentationsconveyedbyLSFsaresufficienttoacti-
factthattheseregionsarerecruitedinavarietyoftasksthatcallon vateasubsetof possiblecandidatesregardingtheidentityof the
contextualassociations,suchasmemoryencoding(Peters etal., visual input (Bar, 2003). These predictions are then projected
2009), navigation (Rauchs et al.,2008; Brown et al.,2010), and back to object recognition regions in inferior temporal cortex,
futurethought(Szpunaretal.,2009). facilitatingperception(Baretal.,2006).
There are several mechanisms by which contextual process- Consistentwiththisproposal,LSFimagesevokeactivityinOFC
ingmaymodulateactivityinregionsrelatedtovisualperception. priortoinferiortemporalareas;thus,LSFinformationreachespre-
PHC itself is situated in the ventral visual stream and lesions frontalcortexquicklyenoughtoinfluencerecognitionprocesses
of this region in the monkey severely impair object recognition intheventralvisualstream(Baretal.,2006).Furthermore,LSF
(Buckley and Gaffan, 1998; Murray and Mishkin, 1998). Thus, imageselicitsignificantfunctionalcouplingbetweenearlyvisual
onepossibilityisthatothercontextnetworkregionsfacilitatethe areasandOFCandbetweenOFCandventralstreamareas(peak-
emergenceofsituation-specificrepresentationsinPHCinatop- ing approximately 85 and 135ms post-stimulus, respectively)
downmanner(Bar,2007;Baretal.,2008).MEGrecordingshave while HSF images do not (Bar et al., 2006). These findings are
shownthatstrongcontextobjectselicitphase-locking(ameasure consistent with the rapid transmission of LSF information to
of functional interaction) between PHC and other context net- OFC, followed by top-down feedback from OFC to the ventral
workregionsasearlyas170msafterstimulusonset(Kveragaetal., stream.
2011),suggestingthattheinteractionbetweentheseregionscan FacilitatoryfeedbackoriginatinginOFChasalsobeenshown
occurearlyenoughtoinfluenceperception.Alternatively,context usingstimulidesignedtopreferentiallystimulatethedorsalmag-
network regions may also influence processing in lateral occipi- nocellular pathway (Kveraga et al., 2007). Magnocellular cells
talcortex(LOC),aregionimplicatedinobjectrecognition(e.g., are sensitive to small differences in luminance contrast but are
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Panichelloetal. Predictionsandconsciousperception
insensitive to color, whereas the parvocellular cells known to predictions may help select the contents of awareness, main-
dominate the ventral stream are sensitive to color but relatively tainingacoherentinterpretationoftheenvironment.Underless
insensitivetoluminance(LivingstoneandHubel,1988).Accord- demandingconditions,predictionsmaystillinfluenceawareness,
ingly, line drawings of objects in which figure and ground are allowingperceptstobegeneratedmorequicklyandwithlessinter-
identicalincolorbutslightlydifferentinluminancepreferentially ference by sensory noise. To support these arguments, we have
stimulatemagnocellularcells(i.e.,“M-biased”stimuli;Steinman drawn on observations from a wide variety of domains,includ-
and Steinman, 1997; Cheng et al., 2004; Kveraga et al., 2007). ingtheresolutionof binocularrivalry,perceptionof ambiguous
Suchstimulicanbeusedtoexaminewhetherthemagnocellular figures, associative learning, and other phenomena. We suggest,
pathwayisindeedimportantforconveyinginformationtoOFC, however,thatallof thesestudiesindexthefactthathumansare
enablingtop-downfacilitation.Indeed,M-biasedstimuliprefer- highly adept at extracting consistencies in the world and using
entially stimulate OFC and elicit functional interaction between thisknowledgetogenerateexpectationsabouttheimmediatesen-
earlyvisualareas,OFC,andinferiortemporalcortex(Kveragaetal., soryenvironment.Althoughdifferentinstancesofpredictionmay
2007).Furthermore,thedegreeofOFCactivationelicitedbyM- recruitdifferentcorticalregions,predictivemechanismsarelikely
biasedstimuliisinverselycorrelatedwithreactiontimeforobject instantiatedasdynamictop-downmodulationof sensorycortex
recognition,suggesting that the processing occurring in OFC is byhighersensoryandprefrontalareasengagedincomparatively
indeedfacilitatingperception(Kveragaetal.,2007).Intriguingly, abstract processing. Via this modulation, predictions about the
despite this facilitation,M-biased stimuli elicited less activity in environmentgeneratedinhigher-levelcorticalregionscanguide
ventral visual regions than stimuli designed to stimulate parvo- perception.
cellularcells,providingindirectevidencethatpredictivefeedback Given that the specific neural processes that give rise to
mayreducetheneedforexhaustivebottom-upprocessingduring conscious perception remain unclear, it is difficult to conjec-
recognition. ture precisely how predictive feedback influences the contents
WehavesuggestedthatLSFrepresentationsinOFCtriggerasso- of awareness.However,itisintriguingthatanumberof promi-
ciationswithobjectandcategoryinformationstoredinmemory, nenttheoriespositthattop-downfeedbackmayplayanimpor-
whichthenserveaspredictionsthatguidesensoryprocessing.To tant role in generating the neural states postulated to account
activatememoryrepresentations,OFCshouldinteractwithhip- for consciousness (Tononi and Edelman, 1998; Lamme, 2010;
pocampalregionsinthemedialtemporallobe,knowntosupport Dehaene and Changeux,2011;Meyer,2012). Indeed,disrupting
long-termmemory(forareview,seeSquireetal.,2004).Indeed, top-down processes seems to impair awareness (Pascual-Leone
OFCandmedialtemporalregionshavebeenshowntoberecip- and Walsh, 2001; Ro et al., 2003; Fahrenfort et al., 2007; Dux
rocally connected in non-human primates (Rempel-Clower and et al., 2010). Perhaps predictions play not only a modulatory
Barbas, 2000). In humans, OFC engages in functional coupling but a driving role in awareness, particularly when other top-
withthemedialtemporallobeduringmemoryretrieval(Nyberg downprocessessuchasattentionarenotengaged.Futureresearch
etal.,1995;Piefkeetal.,2003;TsukiuraandCabeza,2008;Ander- shouldexplorewhetheranindividual’sthresholdforvisualaware-
sonetal.,2010;Colgin,2011).Itwillbeimportanttofurtherclarify nessincreaseswhenpredictiveprocessesareimpaired,suchasin
the possibility that OFC engages in association-based memory depression in which associative processing may be limited (Bar,
retrievalduringvisualperception. 2009).

SUMMARYANDCONCLUSION ACKNOWLEDGMENTS
We have reviewed evidence that predictions have consequences ThisworkwassupportedbyNSFgrantBCS-0842947andDARPA
for conscious perception. When visual input is ambiguous, grantN10AP20036.

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