Visual Perception: Fundamentals of Vision: Low and Mid-Level Processes in Perception

324 Pages·2006·13.475 MB·1-328\324

by  S. Martinez-Conde, S.L. Macknik, L.M. Martinez, J.-M. Alonso and P.U. Tse (Eds.)

List of Contributors
J.-M. Alonso, Department of Biological Sciences, State University of New York—Optometry, 33 West
42nd Street, New York, NY 10036, USA
A. Angelucci, Department of Ophthalmology and Visual Science, Moran Eye Center, University of Utah,
50 North Medical Drive, Salt Lake City, UT 84132, USA
I. Ballesteros-Ya´n˜ez, Instituto Cajal (CSIC), Avenida Dr. Arce 37, 28002-Madrid, Spain
N.E. Barraclough, Department of Psychology, University of Hull, Hull HU6 7RX, UK
A. Basole, Department of Neurobiology, Box 3209, Duke University Medical Center, 427C Bryan
Research Building, Durham, NC 27710, USA
P.C.Bressloff,DepartmentofMathematics,UniversityofUtah,155South1400East,SaltLakeCity,UT
84112, USA
I. Bu¨lthoff, Max-Planck Institut fu¨r biologische Kybernetik, Spemannstrasse 38, D 72076 Tu¨bingen,
Germany
G.P. Caplovitz, Department of Psychological and Brain Sciences, H.B. 6207, Moore Hall, Dartmouth
College, Hanover, NH 03755, USA
M.Carrasco,DepartmentofPsychologyandCenterforNeuralScience,NewYorkUniversity,6Washing-
ton Place, 8th floor, New York, NY 10003, USA
J. De Dios Navarro-Lo´pez, Department of Physiology, University College London, London WC1E
6BT, UK
P. De Weerd, Neurocognition Group, Psychology Department, University of Maastricht, 6200 MD
Maastricht, The Netherlands
J. DeFelipe, Instituto Cajal (CSIC), Avenida Dr. Arce 37, 28002-Madrid, Spain
J.M. Delgado-Garcı´a, Divisio´n de Neurociencias, Universidad Pablo de Olavide, Ctra. De Utrera, Km. 1,
41013-Seville, Spain
R. Engbert, Computational Neuroscience, Department of Psychology, University of Potsdam, 14415
Potsdam, Germany
D. Fitzpatrick, Department of Neurobiology, Box 3209, Duke University Medical Center, 427C Bryan
Research Building, Durham, NC 27710, USA
J.Gyoba,DepartmentofPsychology,GraduateSchoolofArtsandLetters,TohokuUniversity,Kawauchi
27-1, Aoba-ku, Sendai 980-8576, Japan
M.C. Inda, Department of Cell Biology, Universidad Complutense, Madrid, Spain
A. Kitaoka, Department of Psychology, Ritsumeikan University, 56-1 Toji-in Kitamachi, Kita-ku, Kyoto
603-8577, Japan
V. Kreft-Kerekes, Department of Neurobiology, Box 3209, Duke University Medical Center, 427C Bryan
Research Building, Durham, NC 27710, USA
P. Mamassian,CNRSUMR 8581, LPEUniversite´ Paris5,71avenueEdouardVaillant, 92100Boulogne-
Billancourt, France
L.M. Martinez, Departamento de Medicina, Facultade de Ciencias da Sau´de, Campus de Oza,
Universidade da Corun˜a, 15006 La Corun˜a, Spain
ix
x
S. Martinez-Conde, Department of Neurobiology, Barrow Neurological Institute, 350 W Thomas Road,
Phoenix, AZ 85013, USA
A. Mun˜oz, Department of Cell Biology, Universidad Complutense, Madrid, Spain
I. Murakami, Department of Life Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo
153-8902, Japan
F.N.Newell,DepartmentofPsychology,UniversityofDublin,TrinityCollege,ArasanPhiarsaigh,Dublin2,
Ireland
M.W. Oram, School of Psychology, University of St. Andrews, St. Mary’s College, South Street, St.
Andrews, Fife KY16 9JP, UK
A. Pasupathy, Picower Institute for Learning and Memory, Massachusetts Institute of Technology, 77
Massachusetts Avenue, 46-6241, Cambridge, MA 02139, USA
D.I. Perrett, School of Psychology, University of St. Andrews, St. Mary’s College, South Street, St.
Andrews, Fife KY16 9JP, UK
K. Sakurai, Department of Psychology, Tohoku Gakuin University, 2-1-1 Tenjinzawa, Izumi-ku, Sendai
981-3193, Japan
C. Stoelzel, Department of Psychology, University of Connecticut, Storrs, CT 06269, USA
P.U. Tse, Department of Psychological and Brain Sciences, H.B. 6207, Moore Hall, Dartmouth College,
Hanover, NH 03755, USA
C. Weng, Department of Biological Sciences, State University of New York—Optometry, 33 West 42nd
Street, New York, NY 10036, USA
L.E.White,DepartmentofCommunityandFamilyMedicine,PhysicalTherapyDivision,DukeUniversity
Medical Center, Durham, NC 27710, USA
D.Xiao,SchoolofPsychology, UniversityofSt. Andrews, St.Mary’sCollege,SouthStreet, St.Andrews,
Fife KY16 9JP, UK
J.Yajeya, DepartamentodeFisiologı´a yFarmacologı´a,FacultaddeMedicina,Instituto deNeurociencias
de Castilla y Leo´n, Universidad de Salamanca, Salamanca, Spain
C.-I. Yeh, Department of Psychology, University of Connecticut, Storrs, CT 06269, USA
General introduction
‘‘VisualPerception’’isatwo-volumeseriesofProgressinBrainResearch,basedonthesymposiapresented
during the 28th Annual Meeting of the European Conference on Visual Perception (ECVP), the premier
transnational conference on visual perception. The conference took place in A Corun˜a, Spain, in August
2005. The Executive Committee members of ECVP 2005 edited this volume, and the symposia speakers
provided the chapters herein.
Thegeneralgoalofthesetwovolumesistopresentthereaderwiththestate-of-the-artinvisualperception
research, with a special emphasis in the neural substrates of perception. ‘‘Visual Perception (Part 1)’’
generallyaddressestheinitialstagesofthevisualpathway,andtheperceptualaspectsthancanbeexplained
atearlyandintermediatelevelsofvisualprocessing.‘‘VisualPerception(Part2)’’isgenerallyconcernedwith
higherlevelsofprocessingalongthevisualhierarchy,andtheresultingpercepts.However,thisseparationis
not very strict, and several chapters encompass both early and high-level processes.
Thecurrentvolume‘‘VisualPerception(Part1)—FundamentalsofVision:LowandMid-levelProcesses
in Perception’’ contains 17 chapters, organized into 5 general sections, each addressing one of the main
topics in vision research today: ‘‘Visual circuits and perception since Ramo´n y Cajal’’; ‘‘Recent discoveries
on receptive field structure’’; ‘‘Eye movements and perception during visual fixation’’; ‘‘Perceptual com-
pletion’’; and ‘‘Form object and shape perception’’. Each section includes a short introduction and two to
four related chapters. The topics are tackled from a variety of methodological approaches, such as single-
neuron recordings, fMRI and optical imaging, psychophysics, eye movement characterization and com-
putational modeling. We hope that the contributions enclosed will provide the reader with a valuable
perspective on the current status of vision research, and more importantly, with some insight into future
research directions and the discoveries yet to come.
Manypeoplehelpedtocompilethisvolume.Firstofall,wethankalltheauthorsfortheircontributions
and enthusiasm. We also thank Shannon Bentz, Xoana Troncoso and Jaime Hoffman, at the Barrow
Neurological Institute, for their assistance in obtaining copyright permissions for several of the figures
reprinted here. Moreover, Shannon Bentz transcribed Lothar Spillmann’s lecture (in ‘‘Visual Perception
(Part2)’’),andprovidedgeneraladministrativehelp.XoanaTroncosowasheroicinherefforttohelpusto
meetthesubmissiondeadlinebycollatingandpackingallthechapters,andpreparingthetableofcontents.
We are indebted to Johannes Menzel and Maureen Twaig, at Elsevier, for all their encouragement and
assistance; it has been wonderful working with them.
xi
xii
Finally, we thank all the supporting organizations that made the ECVP2005 conference possible: Min-
isteriodeEducacio´nyCiencia,InternationalBrain ResearchOrganization, European OfficeofAerospace
Reseach and Development of the USAF, Consellerı´a de Educacio´n, Industria e Comercio-Xunta de Gali-
cia, Elsevier, Pion Ltd., Universidade da Corun˜a, Sociedad Espan˜ola de Neurociencia, SR Research Ltd.,
Consellerı´adeSanidade-XuntadeGalicia, MindScience Foundation, Museos Cientı´ficosCorun˜eses,Bar-
rowNeurologicalInstitute,ImagesfromScienceExhibition,ConcellodeACorun˜a,MuseoArqueolo´xicoe
Histo´rico-Castillo de San Anto´n, Caixanova, Vision Science, Fundacio´n Pedro Barrie´ de la Maza, and
Neurobehavioral Systems.
Susana Martinez-Conde
Executive Chair, European Conference on Visual Perception 2005
On behalf of ECVP2005’s Executive Committee: Stephen Macknik, Luis Martinez,
Jose-Manuel Alonso and Peter Tse
SECTION I
Visual Circuits and Perception Since
Ramo´ n y Cajal
Introduction
Ramo´n y Cajal is one of the most distinguished visionary insights based purely on observations
scientistsinSpanishhistoryandoneofthegreatest made under a light microscope, still serve as in-
neuroanatomistsofall times.Not surprisingly,any spiration for modern research in the organization,
scientific meeting that takes place in Spain rarely function and development of the visual system.
happens without making a specific mention of the Cajal spent most of his career studying the cir-
outstandingcontributionsofthisscientist.The2005 cuitryofthebrainindifferentspeciesanddifferent
EuropeanConferenceonVisualPerception(ECVP) neural systems with the aid of mostly one method
was no exception. The Symposium ‘Visual circuits — Golgi staining. The philosophy that guided all
and Perception since Ramo´n y Cajal’ started with his work is still valid today — if we want to un-
an acknowledgement of Cajal’s legacy, which was derstand how we perceive, we have to understand
followed by a series of lectures on the study of in detail the circuitry of the visual pathway. The
neural circuitry with modern methods. In 1906, first symposium of ECVP 2005 provided a brief
Ramo´n y Cajal and Camillo Golgi shared the glimpse at some of the new methods that have
NobelprizeinMedicine andPhysiology,while still emerged 100 years after Cajal and that are cur-
maintaining completely opposite views on how the rently used to study neural circuitry. The sympo-
brainisorganized.Cajal’sviewprevailed.Cajalde- sium included approaches that extend from
fended the idea that neurons were separate entities modern neuroanatomical and electrophysiological
in the brain (neuron doctrine) that transmitted in- techniques to recent methods of functional mag-
formationfromthedendritesandsomatotheaxon netic resonance imaging (fMRI) combined with
terminal (law of dynamic polarization). This view psychophysics. The following chapters review the
of the brain, which was revolutionary a century circuitry of different stages in the visual pathway
ago,isnowoneofthebasictenetsofneuroscience. studied using these different methods.
Cajal was not only an outstanding scientist but
also an excellent photographer and artist. His
beautiful drawings of the neural circuits, and his Jose-Manuel Alonso
Martinez-Conde,Macknik,Martinez,Alonso&Tse(Eds.)
ProgressinBrainResearch,Vol.154
ISSN0079-6123
Copyrightr2006ElsevierB.V.Allrightsreserved
CHAPTER 1
Retinogeniculate connections: a balancing act
between connection specificity and receptive field
diversity
J.-M. Alonso1,2,(cid:1), C.-I. Yeh1,2, C. Weng1 and C. Stoelzel2
1DepartmentofBiologicalSciences,SUNYStateCollegeofOptometry,33West42ndStreet,NewYork,NY10036,USA
2Departmentof Psychology,University of Connecticut, Storrs, CT 06269,USA
Abstract: Retinogeniculate connections are one of the most striking examples of connection specificity
withinthevisualpathway.Inalmosteveryconnectionthereisonedominantafferentcellpergeniculatecell,
and both afferent and geniculate cells have very similar receptive fields. The remarkable specificity and
strengthofretinogeniculateconnectionshaveinspiredcomparisonsofthelateralgeniculatenucleus(LGN)
withasimplerelaythat connectstheretinawiththevisualcortex.However, because eachretinal ganglion
cell diverges to innervate multiple cells in the LGN, most geniculate cells must receive additional inputs
from other retinal afferents that are not the dominant ones. These additional afferents make weaker
connections and their receptive fields are not as perfectly matched with the geniculate target as the dom-
inant afferent. We argue that these ‘match imperfections’ are important to create receptive field diversity
amongthecellsthatrepresenteachpointofvisualspaceintheLGN.Weproposethattheconvergenceof
dominantandweakretinalafferentsintheLGNmultiplexesthearrayofretinalganglioncellsbycreating
receptivefieldsthathavearicherrangeofpositions,sizesandresponsetimecoursesthanthoseavailableat
the ganglion cell layer of the retina.
Keywords: thalamus; thalamocortical; visual cortex; V1; Y cell; X cell; response latency; simultaneous
recording
The cat eye has 160,800 retinal ganglion cells that (LGN) (Cleland et al., 1971a, b; Mastronarde,
fit within a retinal area of 450mm2 (Illing and 1992;Usreyetal.,1999).Thesetwomajorchannels
Wassle,1981).One-halfofthesecells(53–57%)has have pronounced anatomical differences. For ex-
small receptive fields and is classified as X and a ample, the X retinal afferents have very restricted
much smaller proportion (2–4%) has larger recep- axon terminals ((cid:1)100mm diameter) that are con-
tivefieldsandisclassifiedasY(Enroth-Cugelland fined to a single layer of LGN and connect small
Robson, 1966; Friedlander et al., 1979; Illing and geniculate cells. In contrast, the Y axon terminals
Wassle, 1981). X and Y retinal ganglion cells are aretwiceaslarge,usuallydivergeintotwodifferent
theoriginof twomajorfunctionalchannels within LGN layers (Sur and Sherman, 1982; Sur et al.,
the cat visual pathway that remain relatively well 1987) and connect geniculate cells with large den-
segregated within the lateral geniculate nucleus dritic trees that tend to cross layer boundaries
(Friedlander et al., 1979; Fig. 1).
(cid:1) XandYretinalganglioncellsdivergeatthelevel
Correspondingauthor.Tel.:[phone];
Fax:[phone];E-mail:[email protected] oftheLGNtoconnectupto20geniculatecellsper
DOI:10.1016/S0079-6123(06)54001-4 3
4
Fig.1. Retinalafferentsandgeniculatecells.Left:axonterminalsfromXandYretinalafferentsinLGN.Xretinalaxonsprojectinto
asingleLGNlayerandtheyareveryrestricted.YretinalaxonscanprojectintotwodifferentLGNlayersandarewider.Middle:
XandYgeniculatecells.XcellshavesmalldendritictreesthatarerestrictedtoasingleLGNlayer.Ycellshavelargerdendritictrees
thatfrequentlycrosslayers.Right:thesameaxonterminalsontheleftofthefigureareshownatadifferentscale.Reprintedwith
permission from Sur and Sherman (1982); Copyright 1982 AAAS; left and right: Sur (1988); middle: Friedlander et al. (1981).
MIN:medialinterlaminarnucleus;PGN:perigeniculatenucleus;I.Z.:interlaminarzone.
retinal afferent (Hamos et al., 1987). This diver- and response latencies that emerge as a conse-
gence could do much more than just copying the quenceofretinogeniculatedivergence/convergence.
properties of each retinal ganglion cell into the
geniculate neurons; it could diversify the spatial
andtemporalpropertiesofthereceptivefieldsthat RetinogeniculatedivergenceintheYvisualpathway
representeachpointofvisualspace.Thisreceptive of the cat
field diversity could then be used at the cortical
level to maximize the spatiotemporal resolution Yretinalganglioncellsareaconspicuousminority
needed to processvisualstimuli. In this review, we within the cat retina (2–4%), which is greatly
illustrate this idea with two different examples. In amplified at subsequent stages of the visual path-
the first example, we show evidence that a single way. While X retinal ganglion cells diverge, on
classofYretinalafferentcanbeusedtobuildtwo average,into1.5geniculatecells,Yretinalganglion
different types of Y receptive fields within the cells diverge into 9 geniculate cells (X geniculate
LGN. In the second example, we show that gen- cells/retinal cells: 120,000/89,000; Y geniculate
iculateneurons representing the same point of vis- cells/retinalcells:60,000/6700;andtheYcellsfrom
ualspacehavearichvarietyofreceptivefieldsizes layer C are not included in this estimate (LeVay
5
and Ferster, 1979; Illing and Wassle, 1981; Peters the Y cell from layer A (Y , shown in orange).
A
and Payne, 1993)). Simultaneous recordings, like the one shown in
The huge amplification of the Y pathway in the Fig. 2, allowed us to compare the response prop-
catisreminiscentofthemagnocellularpathwayin erties from the neighboring Y and Y cells that
A C
the primate. In the rhesus monkey, there is little had overlapping receptive fields. These measure-
retinogeniculate divergence, probably because mentsdemonstratedthat,onaverage,thereceptive
thereisalimitonhowmanyretinogeniculatecon- fieldsfrom Y cellsare1.8timeslargerthanthose
C
nections can be accommodated within the LGN fromY cellsandtheresponselatenciesare2.5ms
A
(the primate retina has 1,120,000 parvocellular faster (po0.001, Wilcoxon test).
cellsand128,000magnocellularcells(seeMasland, The differences in receptive field size and
2001,forreview)). However,asinthe cat,magno- response latency between Y cells located in differ-
cellular cells are a minority within the primate ent layers were sometimes as pronounced as the
retina ((cid:1)8% of all retinal ganglion cells) and, by differences between X and Y cells located within
connecting to magnocellular geniculate cells, they the same layer. To quantify these differences, we
are able to reach a remarkably large number of didsimultaneoustripletrecordingsfromtheneigh-
cortical neurons — at the cortical representation boringY ,Y andX cells1.Fig.3,top,showsan
A C A
of the fovea in layer 4C, magnocellular geniculate example of a triplet recording from three off-
cells connect about 29 times more cortical cells center geniculate cells of different types (X , Y
A A
than parvocellular geniculate cells (Connolly and andY ).TheY cellhadthelargestreceptivefield
C C
Van Essen, 1984). Interestingly, neuronal diver- and the fastest response latency and the X cell the
gence seems to be delayed by one synapse in pri- smallest receptive field and the slowest response
mate withrespect tothecat, asisalso thecasefor latency. For each cell triplet recorded, we calcu-
the construction of simple receptive fields (Hubel lated a similarity ratio to compare the differences
and Wiesel, 2005). between the Y and Y cells with the differences
A C
The cat LGN is an excellent model to study the betweentheY andX cells.Aratiohigherthan1
A A
functional consequences of the Y pathway diver- indicatesthattheY celldifferedfromtheY cell
C A
gence. Unlike the primate, the cat LGN has two morethantheY celldifferedfromtheX cell.As
A A
main layers that receive Y contralateral input showninthehistogramsatthebottomofFig.3,in
(A and C; A1 receives ipsilateral input) and the many cell triplets, thesimilarity ratio forreceptive
retinotopic map of each layer is not excessively field size and response latency was higher than 1.
folded, making it easier to record from multiple Moreover, the mean difference in receptive field
cells with overlapping receptive fields across the size was significantly higher for the Y –Y cells
C A
different LGN layers. Fig. 2 illustrates the retino- thanthatfortheY –X cells(po0.001,Wilcoxon
A A
topic map of cat LGN (Fig. 2A) and the response test). Y and Y cells also differed significantly in
C A
properties of four cells that were simultaneously other properties such as spatial linearity, response
recorded from different layers. The four cells had transience and contrast sensitivity (Frascella and
on-center receptive fields with slightly different Lehmkuhle, 1984; Lee et al., 1992; Yeh et al.,
positions and receptive field sizes (Fig. 2B, left). 2003), and are not illustrated here. These results
Their response time courses, represented as im- indicate that Y retinal afferents connect to two
pulse responses, were also different (receptive
fields and impulse responses were obtained with
white noise stimuli by reverse correlation (Reid 1The precise retinotopy of LGN and the interelectrode dis-
et al., 1997; Yeh et al., 2003)). tances used in our experiments strongly suggest that all our
As showninthe figure, theYcellshadthe larg- recordings came from cells (and not axons) that were located
est receptive fields and fastest response time within a cylinder of o300mm in diameter (Sanderson, 1971).
Recordingsfromaxons, whichwere extremely rare in our ex-
courses within the group. Moreover, the receptive
periments,hadacharacteristicspikewaveform(Bishopetal.,
fieldwaslargerand theresponse latencyfaster for
1962),andcouldnotbemaintainedforthelongperiodsoftime
the Y cell from layer C (YC, shown in green) than neededforourmeasurements.
6
Fig.2. SimultaneousrecordingsfromfourgeniculatecellsrecordedatdifferentlayersinthecatLGN.(A)Left:retinotopicmapofcat
LGN(adaptedfromSanderson,1971).Right:schematicrepresentationofthesimultaneousrecordings.(B)Left:receptivefieldsofthe
foursimultaneouslyrecordedgeniculatecellsmappedwithwhitenoisebyreversecorrelation.Thecontourlinesshowresponsesat
20–100%ofthemaximumresponse.Right:impulseresponsesofthefourcellsobtainedbyreversecorrelation;theimpulseresponse
representsthetimecourseofthereceptivefieldpixelthatgeneratedthestrongestresponse.Thedifferentcelltypesarerepresentedin
differentcolors(XcellfromlayerA,X ,inblue;YcellfromlayerA,Y ,inorange;YcellfromlayerC,Y ,ingreenandWcellfrom
A A C
the deep C layers in pink). Throughout this review, on-center receptive fields are represented as continuous lines and off-center
receptivefieldsasdiscontinuouslines.ReprintedwithpermissionfromYehetal.(2003).
typesofYgeniculatecellswithsignificantlydiffer- A better understanding of how Y and Y re-
A C
ent response properties, Y and Y . ceptivefieldsaregeneratedrequiresaprecisecom-
C A
At firstsight, this conclusion seems atodds with parison of the response properties from Y and
A
the idea that retinogeniculate connections are Y cells that share input from the same retinal
C
highly specific.Ifthereceptivefieldofeachgenicu- afferent.Geniculateneuronsthatshareacommon
lateneuronresemblesverycloselythereceptivefield retinal input can be readily identified with cross-
of the dominant retinal afferent (Cleland et al., correlation analysis because they fire in precise
1971a, b; Mastronarde, 1983; Cleland and Lee, synchrony—theircorrelogramhasanarrowpeak
1985; Usrey et al., 1999), it should not be possible of o1ms width centered at zero (Alonso et al.,
toconstructtwotypesofYreceptivefieldswithone 1996; Usrey et al., 1998; Yeh et al., 2003). Fig. 4
type of Y retinal afferent. Certainly, there is no shows an example of a pair recording from a Y
C
evidence for two types of Y retinal afferents that cell and a Y cell that were tightly correlated (see
A
couldmatchthepropertiesofY andY geniculate narrow peak centered at zero in the correlogram,
A C
receptive fields and almost every Y retinal afferent Fig. 4A, bottom). As expected from cells that
has been found to diverge in the two layers of the share a retinal afferent, the receptive fields of the
LGN (Sur and Sherman, 1982; Sur et al., 1987). Y and Y cells were similar in many respects.
A C
7
Fig.3. ComparisonsofreceptivefieldsizeandresponselatencyobtainedfromtripletrecordingsofY ,Y andX cells.Top:an
A C A
example of a triplet recording from three cells with off-center receptive fields. Receptive fields are shown on the left and impulse
responsesontheright.Bottom:comparisonsofreceptivefieldsize(left)andresponselatency(right).Anindexhigherthan1indicates
thatthedifferencesbetweenY andY werehigherthanthedifferencesbetweenY andX .Anindexlowerthan1indicatesthe
C A A A
opposite. Note that the differences between Y and Y were frequently higher than those between Y and X . Reprinted with
C A A A
permissionfromYehetal.(2003).
They were both off-center and they had similar fieldsizeandresponselatency,probablyowingto
positions in visual space (Fig. 4A, left). On the the inputs from other retinal afferents that were
other hand, the receptive fields showed substan- not shared.
tialdifferencesthatwerereminiscentofthediffer- Interestingly, cell synchrony across layers was
ences between Y and Y cells described above. weaker and more frequently found than cell sync-
A C
For example, the receptive field was larger and hrony within the same layer (when considering
the response latency faster for the Y cell than only cell pairs with480% receptive field overlap).
C
those for the Y cell (Fig. 4A, top). A similar These findings point to a possible mechanism that
A
finding was obtained in recordings from other could allow two types of Y geniculate receptive
Y –Y cell pairs. Y and Y cells sharing a fields to be constructed with one type of Y retinal
C A A C
retinal afferent always had receptive fields of the afferent.Theweakerandmorefrequentsynchrony
same sign (e.g., off-center superimposed with off- across layers could be due to a higher divergence
center) that were highly overlapped (480%). ofYretinalafferentswithinlayerCthanwithinlayer
However, they differed frequently in receptive A. As a consequence of this higher divergence,