prof.dr. e.h.f. de haan utrecht university · prof.dr. d. ballard university of rochester, usa...

Proceedings of the Second Helmholtz Retreat

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Scientific directorProf.dr. E.H.F. de Haan Utrecht University

Members of the boardProf.dr. J.J. Koenderink Utrecht UniversityProf.dr. C.J. Erkelens Utrecht UniversityProf.dr. F.A.J. Verstraten Utrecht UniversityProf.dr. G. F. Smoorenburg [chair] Utrecht UniversityProf.dr. A.V. van den Berg Utrecht UniversityProf.dr. J.J. Bolhuis Utrecht UniversityDr. H. Verschuure Erasmus University RotterdamDr. H. van der Steen Erasmus University RotterdamDr.Ir. J.M. Festen Free University AmsterdamProf.dr.ir. W.A. Dreschler University of Amsterdam

Scientific advisory councilProf.dr. J.J. Eggermont University of Calgary, CanadaProf.dr. Ch.M.M. de Weert University of Nijmegen, The NetherlandsProf.dr. A.D. Milner University of St. Andrews, UKProf.dr. D. Ballard University of Rochester, USAProf.dr. A. Berthoz College de France, Paris FranceProf.dr. H. Bülthof Max Planck Institut für Kybernetik, Germany

Office managementMrs. V. Maassen-Monrooij Utrecht University

Special thanks toVeronica Maassen-Monrooij


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Proceedings of the SecondHelmholtz Retreat

23-25 June 2003

BergenThe Netherlands

Organizedby

Frans Verstraten


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Contents

Welcome 5

The keynote speakers 6

List of participants 8

Program 10

Program & Abstracts 13


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Welcome…

The second conference of the Helmholtz Research School is set tobecome a success. The current format combines what went well duringthe first meeting in Schiermonnikoog two years ago with new ideas toimprove the meeting. The programme looks interesting and stimulating,and the venue looks like a very agreeable place to be.

The aim of this conference remains fourfold. First, it is an opportunity toinform one another within the school of current research progress.Second, it is a platform for consolidation and strengthening ofcollaborative research between the groups that together form theHelmholtz School. Third, it is intended as a stage for young scientists tolearn to present their research to a wider audience than their own group,and last but not least, it gives the members of the School a chance toenjoy themselves and meet colleagues in a pleasant environment.

The Helmholtz School stands for high quality research and PhD training and this conference plays acentral role in this endeavour. I would like to thank Frans Verstraten for organising the meeting and Iwant to urge the delegates to attend all the sessions. There is a lot to be learned from studies outsideyour direct field of interest.

On behalf of the board and the education committee, I want to welcome you all to the secondHelmholtz Retreat in Bergen,

Edward de Haan

Scientific director of the Helmholtz Institute


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Our keynote speaker I

Mary Hayhoe

PhD. University of California, San Diego, 1979.

Professor of Brain & Cognitive Sciences,Computer Science and Center for Visual Science.University of Rochester.

Vision naturally occurs in the context of voluntaryinformation gathering movements involving theeyes, head, and hand. However, much work invision is dominated by trying to understand theevents occurring within a single view of a scene, andwe have only limited understanding of theconsequences of eye and head movements for visionand visuo-motor coordination. The technology to

look at performance in more natural circumstances now exists, and I am currentlydeveloping a human sensory-motor lab, in collaboration with Dana Ballard inComputer Science, for measuring unconstrained eye, head, and hand movements inthe performance of natural tasks, and for developing a virtual reality display to allowcontrolled but visually complex stimulation. The new instrumentation allows a largerange of experiments not previously possible. My objective is to understand thedemands placed on the visual system by natural behavior and the nature of therepresentations that are required for visually guided tasks.

More information can be found on Mary's web-page:http://www.bcs.rochester.edu/people/mary/mary.html


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Our keynote speaker II

Dana H. Ballard

PhD. University of California at Irvine, 1974.

Professor of Computer Science, Brain andCognitive Science, Center for Visual Science.University of Rochester.

Dana Ballard's primary interests are the models ofthe brain that relate detailed processing ofinformation at the neural level to interestingbehavior. The principal technical focus of Dana'swork is in information hierarchies, with the specificgoal of understanding the physical constraints thatmake hierarchical systems advantageous. He haschampioned a particular scheme of representing

information in the cortex that was suggested by Barlow and has argued for itsgenerality.

Dana Ballard is author of the book Introduction toNatural Computation (MIT Press, 1997)

Moreover, he is a member of the Scientific AdvisoryCouncil of the Helmholtz Research Institute.

More information can be found on his web-page:http://www.cs.rochester.edu/u/dana/home.html


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List of ParticipantsAivar, Pilar Post-doc EURAleman, Andre Assistant Professor UU-PSNBaas, Daan Ph.D student UU-PSNBallard, Dana Professor URochesterBeintema, Jaap Post-doc UU-FNBiegstraaten, Marianne Ph.D student EURBours, Roger Ph.D student UU-FNBraskamp, Jan Ph.D student UU-FNBrenner, Eli Assistant Professor EURBrouwer, Gijs Ph.D student PMCuijpers, Raymond Post-doc EURDe Grave, Denise Ph.D student EURDe Haan, Edward Professor UU-PSNDoumen, Michelle Ph.D student UU-PMDubbelboer, Finn Ph.D student VUDuijnhouwer, Jacob Ph.D student UU-PMEeuwes, Lonneke Ph.D student UU-FNErkelens, Casper Professor UU-PMFesten, Joost Associate Professor VUFrens, Maarten Associate Professor EURGheorghiu, Elena Ph.D student UU-PMGranzier, Jeroen Ph.D student EURGrol, Meike Ph.D student UU-PSNHayhoe, Mary Professor URochesterHermans, Erno Ph.D student UU-PSNHermens, Frouke Ph.D student UU-PMHilkhuysen, Gaston Ph.D student VUHooge, Ignace Assistant Professor UU-PSNHouben, Rolph Ph.D student UU-AUKanai, Ryota Ph.D student UU-PSNKappers, Astrid Associate Professor UU-PMKessels, Roy Assistant Professor UU-PSNKhang, Byung-Geun Post-doc UU-PMKenemans, Leon Professor UU-PSNKlis, Sjaak Associate Professor UU-AUKnapen, Tomas Ph.D student UU-PMKoenderink, Jan Professor UU-PMKroeze, Jan Professor UU-PSNLankheet, Martin Associate Professor UU-FNLansbergen, Marieke Ph.D student UU-PSNLopez-Moliner, Joan Post-doc EURLorteije, Jeanette Ph.D student UU-FNLouw, Stefan Post-doc EURNefs, Harold Post-doc UU-PMNoest, Andre Post-doc UU-FNNiewenstein, Mark Ph.D student UU-PSNNijboer, Tanja Ph.D student UU-PSNNys, Gudrun Ph.D student UU-PSNNoordzij, Matthijs Ph.D student UU-PSNOver, Eelco Ph.D student UU-PMOvervliet, Krista Ph.D student EURPaffen, Chris Ph.D student UU-PSNPerge, Janos Ph.D student UU-FNPeters, Rob Associate Professor UU-FNPoljac, Ervin Ph.D student UU-FNPostma, Albert Associate Professor UU-PSN


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Putman, Peter Ph.D student UU-PSNRhebergen, Koen Ph.D student AMCRijkaart, Dorien MSc Student EURRoessingh, Jan-Joris Post-doc UU-PMRotman, Gerben Ph.D student EURSchutter, Dennis Ph.D student UU-PSNSlijper, Harm Post-doc EURSmeets, Jeroen Assistant Professor EURSmoorenburg, Guido Professor UU-AUSouman, Jan Ph.D student UU-PSNTe Pas, Susan Assistant Professor UU-PSNTolboom, Michiel Ph.D student UU-FN’t Wout, Masha Ph.D student UU-PSNVan Beers, Rob Post-doc EURVan Beurden, Maarten Ph.D student AMCVan Dam, Loes Ph.D student UU-PMVan de Berg, Bert Professor UU-FNVan den Dobbelsteen, John Post-doc EURVan der Geest, Jos Post-doc EURVan der Lubbe, Rob Post-doc UU-PSNVan der Smagt, Maarten Assistant Professor UU-PSNVan Ee, Raymond Assistant Professor UU-PMVan Honk, Jack Assistant Professor UU-PSNVan Ruyven, Marjolijn Ph.D student UU-AUVan Wezel, Richard Assistant Professor UU-FNVan Zandvoort, Martine Assistant Professor UU-PSNVeldhuizen, Marga Ph.D student UU-PSNVersnel, Huib Assistant Professor UU-AUVerstijnen, Ilse Assistant Professor UU-PSNVerstraten, Frans Professor UU-PSNWertheim, Lex Professor UU-PSNWinkelman, Beerend Ph.D student EURZuidhoek, Sander Ph.D student UU-PSN

AMC = Academic Medical Center Amsterdam – Audiology UvAEUR = Erasmus University Rotterdam – Department of NeuroscienceUU-FN = Utrecht University – Functional Neurobiology DivisionUU-PM = Utrecht University – Physics of Man DivisionUU-AU = Utrecht University – Hearing Research LaboratiesUU-PSN = Utrecht University – Psychonomics DivisionVU = Free University Amsterdam – Audiology


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ProgramMonday 23 JUNE

Session 1(Moderator: Richard van Wezel)10.45 – 11.00 Raymond van Ee – Topical introduction perceptual motor integration group11.00 – 11.15 Eelco Over – Visual span and eye movements11.15 – 11.30 Elena Gheorghiu – Depth from fast alternating disparities11.30 – 11.45 Tomas Knapen – Influence of depth perception on binocular eye movements11.45 – 12.00 Loes van Dam – Psychophysics of bi-stable depth perception12.00 – 12.15 Gijs Brouwer – Neurophysiology of bi-stable depth perception

12.30 – 14.00 Lunch & sniff-some-good-air-time

Session 2(Moderator: Leon Kenemans)14.00 – 14.15 Bert van den Berg – Lifting visual signals off their retinal base?14.15 – 14.30 Andre Noest – Metric shape-in-depth from disparity and vergence14.30 – 14.45 Ervin Poljac – The representation of visual stimuli for goal-directed arm

movements in near head space14.45 – 15.00 Jacob Duijnhouwer – Spatiotopic motion processing

15.00 – 15.30 Refreshments

15.30 – 15.45 Rob Peters – Electroreception and hearing in fishes15.45 – 16.00 Lonneke Eeuwes – Is the bio-electric field of a catfish representative for

measuring stress?

16.00 – 17.30 Walk on the beach/drinks/whatever you feel like

18.00 – 19.45 Diner

(Moderator: Eli Brenner)20.00 – 20.30 Pilar Aivar – Helmholtz’s explanations of space perception: nativism versus

empirism

(Moderator: Jeroen Smeets)20.30 – 21.30 VISUAL MEMORY AND ATTENTION IN NATURAL TASKS

INVITED LECTURE BY PROFESSOR MARY HAYHOE(Universtiy of Rochester, New York, USA)

22.00 - ??? Drinks and social gathering


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Tuesday 24 JUNE

06.00 – 07.00 Early bird beach walk/run/swim07.00 – 08.45 Breakfast

Session 3(Moderator: Ignace Hooge)09.00 – 09.15 Joost Festen – Psychoacoustics in the Helmholtz Core Program in Audiology

(HCPA)09.15 – 09.30 Rolph Houben – The effect of amplitude compression in hearing aids on speech

intelligibility in noise09.30 – 09.45 Maarten van Beurden – Loudness measuring procedures09.45 – 10.00 Finn Dubbelboer – Speech intelligibility after digital processing10.00 – 10.15 Koen Rhebergen – Prediction of the speech intelligibility under masking

conditions10.15 – 10.30 Gaston Hilkhuysen – Clinical measurement of spectral and temporal resolutions in

hearing


Session 4(Moderator: Guido Smoorenburg)11.00 – 11.15 Ignace Hooge – Introduction: cycling to the Uithof from home11.15 – 11.30 Ryota Kanai – Offset signals of visual object trigger perceptual fading11.30 – 11.45 Christiaan Paffen – Binocular rivalry between moving stimuli: the effect of

surround motion11.45 – 12.00 Mark Nieuwenstein – Temporal limitations in conscious visual perception reflect

attentional inertia12.00 – 12.15 Jan Souman – A 2D-model of motion perception during smooth pursuit eye

movements

12.30 – 14.00 Lunch & sniff-some-fresh-air-time

Session 5(Moderator: Raymond van Ee)14.00 – 14.15 Jac van Honk – The neurobiology of emotion14.15 – 14.30 Dennis Schutter – A functional connectivity model of depression14.30 – 14.45 Peter Putman – Reflexive orienting in response to emotional eye gaze14.45 – 15.00 Erno Hermans – Central effects of testosterone on emotional processing as

measured by fMRI


Session 6(Moderator: Astrid Kappers)15.30 – 15.45 Byung-Geun Khang – Perception of illumination direction in 3-D shaded image15.45 – 16.00 Michelle Doumen – Visual space under free viewing conditions16.00 – 16.15 Sander Zuidhoek – Haptic space: the role of visual processing16.15 – 16.30 Matthijs Noordzij – Properties of spatial mental models of blind and sighted

people

16.30 – 18.00 Karate!!!!/walk on the beach/drinks/whatever you want to do

18.00 – 19.45 Diner

(Moderator: Jan Koenderink)20.00 – 21.00 TOWARDS COMPLETE MODELS OF HUMAN VISUAL-MOTOR

BEHAVIORSINVITED LECTURE BY PROFESSOR DANA BALLARD(Universtiy of Rochester, New York, USA).


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Wednesday 25 JUNE

06.00 – 07.00 Beach exercise/walk/Swim07.00 – 08.45 Breakfast

Session 7(Moderator: Roy Kessels)08.45 – 09.00 Hans van der Steen – Research in Rotterdam (Eli Brenner)09.00 – 09.15 Gerben Rotman – Eye orientation information for localising visible stuctures etc.09.15 – 09.30 Denise de Grave – The Ebbinghaus figure is more than a size illusion09.30 – 09.45 Jeroen Granzier – Color induction

09.45 – 09.55 Short break

Session 8(Moderator: Maarten Frens)09.55 – 10.10 Marianne Biegstraaten – Müller-Lyer and grasping: Illusion or obstacles?10.10 – 10.25 Dorien Rijkaard – Cervico-Ocular-Reflex adaptation10.25 – 10.40 Beerend Winkelman – The complex spike code


Session 9(Moderator: Martine van Zandvoort)11.00 – 11.15 Richard van Wezel – Motion processing in cortical areas MT and MST11.15 – 11.30 Janos Perge – Direction tuning of macaque MT neurons: a reverse correlation

study11.30 – 11.45 Roger Bours – Speed tuning of neurons in macaque MT11.45 – 12.00 Jeanette Lorteije – Implied motion in macaque area MT and MST12.00 – 12.15 Jaap Beintema – Rivalry in biological motion

12.30 – 14.00 Lunch & sniff-some-good-air-time

Session 10(Moderator: Frans Verstraten)14.00 – 15.00 Discussion & Wrap up.

15.00 – … Whatever you feel like…!


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Program & AbstractsMonday 23 JUNE

Session 1 (Moderator: Richard van Wezel)

10.45 – 11.00 Raymond van Ee -Topical introduction perceptual motor integration group11.00 – 11.15 Eelco Over - Visual span and eye movements11.15 – 11.30 Elena Gheorghiu - Depth from fast alternating disparities11.30 – 11.45 Tomas Knapen - Influence of depth perception on binocular eye movements11.45 – 12.00 Loes van Dam - Psychophysics of bi-stable depth perception12.00 – 12.15 Gijs Brouwer - Neurophysiology of bi-stable depth perception

10.45 – 11.00. Raymond van Ee -Topical introduction perceptual motor integration group (co-author Casper Erkelens).

In the Erkelens/van Ee group we ask how visual information is processed for perception and motorbehavior. One of the tasks in which perceptual and motor information is integration is visual search.In addition, perceptual stereoscopic illusions provide us a window of how the information isintegrated. An overview of the group's combined effort to address these issues will be presented.

11.00 – 11.15 Eelco Over - Visual span and eye movementsThe “visual span” (the area around the fixation location in which targets can be found) has beenreported to differ in size considerably between subjects (Reingold et al., 2001). It is also known thatvisual spans can influence reaction times in single fixation search experiments (e.g. Zelinsky &Sheinberg, 1997), probably due to expansion of the visual span during fixation (Geisler & Chou,1995). Are these findings important for eye movement parameters such as saccadic amplitude? In asimple search experiment fixation duration was manipulated by instructing subjects to make eyemovements at the pace of a metronome. Eye movements made at a slow pace imply long fixationdurations (since saccadic times are fixed) and large visual spans. Eye movements made at a fast paceimply short fixation durations and small visual spans. If search is effective, saccadic amplitudesshould be larger at slow pace than at fast pace. Our results do not confirm this prediction. This meansone of two things: 1) the size of the visual span does not heavily depend on fixation duration or 2)visual span size is not an important factor for eye movement parameters. We suggest that saccadeamplitudes are more influenced by search strategy than visual span size.

11.15 – 11.30 Elena Gheorghiu - Depth from fast alternating disparities (co-author: CasperErkelens)

We observed that two disparity-defined depth planes in which the disparity was induced bysymmetrical displacements between the left and right eyes’ images were perceived at a single depthwhen disparity alternated rapidly between two values. We observed two transparent depth planeswhen the displacements were asymmetrically distributed between the left and right eyes’ images. Weinvestigated quantitatively how depth of the planes depended on the temporal frequency of disparityalternation. We alternated the two disparity values between 6 Hz and 35 Hz. We used two types ofdynamic random - dot stereograms. In one stereogram, a single pattern alternated between twodisparity values. In the other stereogram we alternated two uncorrelated patterns each having one ofthe two disparity values. We employed a depth discrimination task between the test plane and a staticreference plane. The results show that the perceived depths depend on the type of stereogram. Theresults indicate that stereopsis results from monocular temporal integration of luminance followed bya cross-correlation-like operation on two simultaneous, monocular inputs. Therefore, temporalprocessing of disparity is limited by temporal properties of monocular luminance mechanisms.

11.30 – 11.45 Tomas Knapen - Influence of depth perception on binocular eye movementsWe recorded vergence responses of binocular saccades under monocular viewing conditions. Canmonocular images (containing only monocular cues to depth: perspective) produce appropriatevergence-responses (Enright, 1987)? The Necker-cube is an ambiguous figure that allows twodifferent/opposite depth interpretations. We asked subjects to make saccades between two specifiedpoints ONLY when they were in 'one of the two possible 3D-percepts'. By removing some lines of thefigure, the cube becomes non-ambiguous. Furthermore, observers can imagine a depth differencebetween two isolated points. We compared the vergence responses for these different conditions.


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11.45 – 12.00 Loes van Dam - Psychophysics of bi-stable depth perception (co-author Raymondvan Ee)

We exposed the visual system to an ambiguous 3D stimulus consisting of a grid for which monocularand binocular cues could specify different slants about a horizontal axis. Observers were asked toestimate the slant of the grid in 3D space. Monocular and binocular specified slants were variedindependently across stimulus presentations. When monocular and binocular cues specified similarslants (no conflict) observers perceived a single orientation. However when the difference betweenthe specified slants was large (cue-conflict), observers were able to select either a monocular or abinocular dominated percept. This result corroborates what van Ee, van Dam and Erkelens (Journal ofVision, 2002, 2, 597-607) reported for slants about a vertical axis. Eye movement measurementsrevealed that (1) the flipping between percepts can occur under strict fixation and (2) when eyemovements are allowed, saccades and blinks do not increase the likelihood of perceptual flips.Therefore we suggest that perceptual flipping of the bistable grid stimulus is a central process inwhich eye movements are not necessarily involved.

12.00 – 12.15 Gijs Brouwer - Neurophysiology of bi-stable depth perceptionUsing our novel bistable stimuli and functional magnetic resonance imaging (fMRI), we investigatedthe neural correlates of bistable depth perception. The stimuli used were wireframe planar grids,presented dichotopically by using a conventional red-green anaglyphic technique (see abstracts of vanEe and van Dam). The perceived slant of the grid (rotation about the z-axis of the frontoparallelplane) was manipulated using two depth cues: foreshortening (monocular perspective) and disparity(binocular stereopsis). Both depth cues indicated either a slant of 70 or -70 degree rotation. Whenboth depth cues are congruent, the stimulus is stable and perceived as a rectangular grid, rotated aboutthe z-axis of the frontoparallel plane. When the depth cues are made to be incongruent, the stimulusbecomes bistable and is perceived either as a slanted rectangular wireframe grid (perspectivedominated percept) or as a slanted trapezoid wireframe grid (disparity dominated percept).Using fMRI we found that viewing of the bistable version of our stimulus (compared to the stableversion) causes an increase of neural activity in a number of cortical areas. These areas includeobject-related areas in ventral occipital and ventral temporal cortex, activity in the parietal cortex(near the intraparietal sulcus) and several areas in the prefrontal cortex. When compared to literature,this pattern of activity is similar to the pattern of activity found for other bistable stimuli.

Session 2 (Moderator: Leon Kenemans)

14.00 – 14.15 Bert van den Berg - Lifting visual signals off their retinal base?14.15 – 14.30 Andre Noest - Metric shape-in-depth from disparity and vergence14.30 – 14.45 Ervin Poljac - The representation of visual stimuli for goal-directed arm movements

in near head space14.45 – 15.00 Jacob Duijnhouwer - Spatiotopic motion processing15.30 – 15.45 Rob Peters - Electroreception and hearing in Fishes15.45 – 16.00 Lonneke Eeuwes - The Bioelectric field: origin and function in aquatic organisms

14.00 – 14.15 Bert van den Berg - Lifting visual signals off their retinal base?The moving observer receives a complex visual flow. The ‘ecological’ approach to vision, asconceived by Gibson, emphasized the tuning of the visual system to those properties of the visualstimulus that are invariant under gaze movement or gaze displacements. This led Gibson and hisfollowers to formulate many such invariants informative of ego-movement and the layout of theenvironment. More recent studies reemphasize the older views by Helmholtz and Von Holst, thatretinal signals and motor signals on the eye and head orientation merge in our visual percepts. Thisleads to the question what kind of visuo-motor invariants one can formulate to explain perceptualconstancy despite eye movement.The question relates to the general problem what kind of processing strategy the brain uses to blendstreams of information that have widely different formats. This problem arises regularly in the contextof multi-sensory information processing. For example, the blending of eye centred visual and headcentred auditory information on where an object is. Likewise, the formats of the eye position orvelocity related signals and visual signals are also widely different. Eye position (velocity) signalsspecify information that is mathematically equivalent to a single vector that represents the spin of theeye (the components of rotation about a horizontal, vertical and a torsional axis). Visual information,however, consists of a map of visual direction, angular motion or retinal disparity vectors.Neurophysiological studies indicate that the brain modulates visual signals by eye signals causing so


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called gain-fields. Such computations can be useful to compute visuo-motor invariants of thefollowing kind: O - dO/dE e + 0.5 d2O/dE2 e 2 .....

Where e stands for the eye signal and O for some visually receptive unit and its derivatives withrespect to the eye position (movement). This invariant sum can reflect the activity of a dynamicreceptive field, that maintains an invariant view relative to the head, the activity of a unit that isdynamically tuned to the changing retinal flow when an eye rotates or the changing disparity field ofa 3D object when eye vergence changes. I will briefly indicate what kind of approaches we take toinvestigate these ideas further.

14.15 – 14.30 Andre Noest - Metric Shape-in-Depth from Disparity and Vergence. (Co-authorA.V. van den Berg)

Recovering the metric depth-structure of objects from horizontal disparities requires a transformationinvolving the viewing distance, which is available from e.g. ocular vergence signals or verticaldisparity gradients. We report adaptation experiments which strongly suggest that the brain computesthe required transformation of curvature-in-depth within a coordinate frame based on (cyclopic)retinal directions, not in a head-centric frame. Indeed, we find that human adaptation to curvature-in-depth transfers almost fully across a large change in head-centric direction. Nevertheless, adaptationalso proves resistant to ‘smearing’ the local retinal disparity values by fixating on a target thattraverses the stimulus in depth as well as laterally. Other hints about the neural representation andprocessing that implements the required transformation are: (i) Domini's finding that the adaptationdepends on the curvature of the object, not that of the disparity-field; and (ii) Trotter'sneurophysiology results in macaque V1: Binocular cells are mostly tuned to a fixed disparity, buttheir gain is modulated by ocular vergence.We propose a neural model which unites and explains these data, and predicts a next stage of cellswith disparity-pattern receptive fields whose shape is dynamically controlled by ocular vergence: Afield of local, rate-coded object-curvature values is computed in one step by neurons whose inputs arethe usual field of population-coded disparities in the cyclopic retinal frame. It is essential that thisdisparity field is coded by neurons with monotonic gain-modulation by vergence, since this allows thesecond layer of neurons to extract in one step the object- instead of the disparity -curvature, asfollows: Receptive fields defined by orthogonal pairs of 1st and 2nd Gaussian derivatives extract thecurvature of iso-activity contours in a population code. Acting on a fixed-gain disparity code, thesereceptive fields would extract local disparity-curvatures, but with a smoothly vergence-driven gain-modulated code, they can extract local object-curvatures instead. Neural adaptation at the first andsecond stages then explains the psychophysical results.

14.30 – 14.45 Ervin Poljac - The representation of visual stimuli for goal-directed arm movementsin near head space

Perception of the world around us remains stable, despite constant movements of our eyes. Helmholtzproposed that a copy of the motor command is sent to visual areas and modulates activity of the cellsto achieve constancy, which has been confirmed in various neurophysiological studies. One possiblestrategy to achieve a constant percept is retinal updating. Visual signals remain in essentially a retino-centric format, but the retina-based signals are updated to take the displacements of the eye intoaccount. For example, for goal directed arm movements, such as pointing, behavioral experimentshave suggested that remembered visual targets in far space are encoded in a retinal frame. The secondpossibility is to use eye position signal to transform the reference frame from one that is retinotopicinto head or other body centric frame of reference. Interaction between visual and eye orientationsignals results in a so called eye position gain field, that serves as a first step for such a transformationtowards a head centric visual representations. Neurophysiological studies in monkey have identifiedan area (VIP) in the posterior parietal cortex that contains cells with head centric receptive fields fornear visual stimuli (Duhamel et al. 1997). This could mean that a transformation of visual space fromretinocentric to a head centric representation may be involved for visual objects in close proximity ofthe head. Are remembered visual targets for pointing in near space encoded in a head centric frame?To investigate this, subjects had to point towards an initially foveated central target after anintervening saccade. Subjects made errors which reflect a bias in the visuo-motor transformation thatdepends on eye displacement rather than any head-centered variable. Also in near space, therepresentation of visual stimuli for goal-directed arm movements seem to rely on retinal updating.

14.45 – 15.00 Jacob Duijnhouwer - Spatiotopic motion processingThe human observer perceives the world around him to be stable, despite its many eye, head, and,body movements. This suggests that at some point in the visual pathway the retinal input is converted


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to a spatiotopic frame of reference. The modulation of neuronal responses to visual stimuli by thedirection of gaze found in physiological studies on monkeys is considered to be a first step in thisconversion. A recent psychophysical study showed that gaze direction modulates the magnitudes ofvisual aftereffects in human observers, establishing its role in human visual perception [Nishida et al,Vis. Res. 43 (2003)]. Here we show that motion can induce an aftereffect in retinally unadapted partsof the visual field when the test stimulus is presented at the same spatiotopic location as the adaptingstimulus.

15.30 – 15.45 Rob Peters – Electroreception and hearing in fishesThe electric sense and the sense of hearing in fishes share a common ontogenetic origin. Both sensorysystems belong to the octavo-lateral system (acustico-lateral system in the early days). Octavo-lateralsense organs have 'hair cells' as receptor cells, but respond to a variety of sensory stimuli which aredescribed as sound, water current, electric fields, gravitational and rotational forces and other stimuli.Both sensory systems illustrate how a single basic genetic design can differentiate into sensorysystems with specific adaptations to the environment. This presentation will briefly highlight currentresearch at Utrecht University on electroreception and hearing in freshwater fishes.

15.45 – 16.00 Lonneke Eeuwes - The Bioelectric field: Origin and function in aquatic organismsElectrosensitive fish have specialized electroreceptor organs to detect electrical stimuli in theirenvironment. Some of these species have electric organs that can emit either strong (~ 600 V) or weak(~ 5V) electric discharges (EODs), which are used in defense, communication, and orientation.Species without electric organs utilize their electroreceptor organs to detect environmental fields ofgeochemical origin, and the bioelectric fields that surround all aquatic organisms. In this manner, theycan orient in their habitat, and localize their prey even if these are camouflaged or hard to detect withother senses, e.g. in murky water. Although bioelectric fields of fish have been studied in the past inthe context of electroreception, little is known about its origin, stability, and the behavioral relevanceof its dc- or ac-component. Furthermore, the bioelectric fields of electrosensitive fish themselves arenot yet investigated, even though they are sufficiently strong to stimulate the electroreceptor organs ofconspecifics (and hence could serve as a communication signal). In my research, the origin andbiological significance of bioelectric fields in aquatic organisms is investigated. The catfish, Ictalurusnebulosus, is used as a model for electrosensitive freshwater fish. The dc-component of the bioelectricfield is thought to originate from biochemical processes that take place during osmoregulation, herebygenerating transepithelial potentials, whereas the ac-component is caused by respiratory movements.The bioelectric dc-field is variable in strength, due to a variety of factors such as arousal, feeding, andwater composition. The relation between these factors, the bioelectric dc-field of fish, and epithelialtransport is investigated. The main focus of the project sofar lies on the shape and strength of thebioelectric dc-field in catfish under normal conditions and stressful conditions, the latter induced bycortisol-injections.


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Evening Program Monday

Invited Speaker (Moderator: Eli Brenner)

20.00 – 20.30 Pilar Aivar - Helmholtz’s explanations of space perception: nativism versusempirism

In this talk I will discuss some of Helmholtz’s empiristic views about the visual perception of space. Iwill show how Helmholtz considered that space was an empirical result of the functional coordinationof the retinal stimulation obtained in each moment and our own eye movements, and therefore anactive and continuous process. His explanations will be related to the opposite, nativistic, point ofview, defended at that moment by Hering. In a more general sense, some relations will be establishedbetween both points of views in the explanation of space, nativistic and empiristic, and the influenceof Kant on the development of the field of psychology during the 1850s.

Keynote-Lecture 1 (Moderator: Jeroen Smeets)

20.30 – 21.30 VISUAL MEMORY AND ATTENTION IN NATURAL TASKSINVITED LECTURE BY PROFESSOR MARY HAYHOE(Universtiy of Rochester, New York, USA)

Traditionally, visual processing has been thought of as parallel and high capacity, whereas cognitivemechanisms are sequential and capacity limited. How the interface occurs is a matter of considerabledebate, and recent work showing profound attentional effects in early visual areas shows that it is notreally possible to consider vision and cognition separately. The tension is reflected in the body ofwork on "change blindness", which shows that observers are extremely insensitive to changes in thevisual scene made during an eye movement, film cut, or similar masking stimulus. This work impliesthat visual representations may be extremely limited, a finding that conflicts with the implicitassumption that vision somehow provides a complete representation of the visual scene. It seemslikely that resolution of these issues requires a consideration of the functional context of the observer.This emerges as a natural organizing principle when one considers ordinary behavior. In anexperiment where subjects picked up objects in a virtual environment with haptic feedback andmoved them across the field, we occasionally made substantial changes in the size of the objectduring the movement. Subtle differences in instruction that define the time during the task whenobject size is relevant, lead to substantial differences in awareness of these size changes, even thoughthe object was the focus of attention throughout the trial. This suggests that the role of attention needsto be more tightly defined. We postulate that the underlying determiner for what visual information isrepresented is exactly what tasks, or visual computations, the observer is engaged in from moment tomoment (for example: determine object size, select object, fixate object, program reach and grasp topick up object, select location for putdown etc). That is, the task micro-structure determines both whatis attended, and what is remembered. The dynamic and task-specific nature of visual representationswas also demonstrated in another experiment using a virtual driving enviroment. Briefly presentedStop signs do not attract gaze unless they are both relevant to the task and in a likely location, andobservers deploy quite different gaze patterns depending on task goals. This suggests that theinformation acquired from natural environments is under the control of learnt behavioral programsthat determine when an active search for specific information is executed.


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Tuesday 24 JUNE

Session 3 (Moderator: Ignace Hooge)

09.00 – 09.15 Joost Festen - Psychoacoustics in the Helmholtz Core Program in Audiology (HCPA)09.15 – 09.30 Rolph Houben - The effect of amplitude compression in hearing aids on speech

intelligibility in noise.09.30 – 09.45 Maarten van Beurden - Loudness measuring procedures09.45 – 10.00 Finn Dubbelboer - Intelligibility of speech in noise after digital processing10.00 – 10.15 Koen Rhebergen - Prediction of the speech intelligibility under masking conditions10.15 – 10.30 Gaston Hilkhuysen - Clinical measurement of spectral and temporal resolutions in

hearing

09.00 – 09.15 Joost Festen - Psychoacoustics in the Helmholtz Core Program in Audiology(HCPA)

Psychoacoustics, as a branch in psychophysics, originally studies characteristics and functionality ofthe ear by regarding it as a ‘black-box’ and investigating the changes in perception from manipulationof input signals. Perception is evaluated with sophisticated techniques, originating from signaldetection theory, in which methods are applied that can eliminate response bias from the results.Modern psychoacoustics is no longer strictly limited to the black box approach. Generally, ourunderstanding of hearing is strongly influenced by findings from physiology. This development isalso apparent in the research collaboration on audiology of four academic ENT departments in theHelmholtz research school. Each year these audiology groups meet several times in the HelmholtzCore Program in Audiology to exchange ideas and to train AIO’s in presenting their results. Theresearch in this program is mainly focused on hearing impairment, its origin, the consequences forspeech perception, and the possibilities for rehabilitation. This session of the retreat will present aselection of studies from this field.

09.15 – 09.30 Rolph Houben - The effect of amplitude compression in hearing aids on speechintelligibility in noise. (co-author Guido Smoorenburg)

Modern hearing aids often use compressive amplification. This type of signal processing reduces thedynamic range by reducing the signal amplitude at high input levels selectively, following byamplification of the manipulated signal. A dynamic range reduction is thought to be particularlyuseful for hearing impaired persons who suffer from sensorineural hearing loss. This type of hearingloss, which can be caused by, e.g., aging, noise exposure, and ototoxic medication, originates fromwithin the cochlea and is often accompanied by a reduced dynamic range in auditory perception.In this research the influence of several relevant compression parameters on speech intelligibility innoise was investigated. The effects of compression ratio, time constants, and the number of channelswere systematically evaluated. Nineteen subjects with moderate sensorineural hearing loss havecompleted the experiment. First results show that with respect to speech intelligibility in noise,compressive amplification does not yield better results than linear amplification at optimal levels.

09.30 – 09.45 Maarten van Beurden - Loudness measuring proceduresLoudness is the subjective judgement of the intensity of a sound. But besides intensity, alsobandwidth, duration, frequency and temporal structure influence our loudness sensation. Severaldifferent procedures have been developed to investigate loudness and one of these procedure isloudness matching. This is a procedure in which a subject has to compare the loudness of two sounds.When using a matching procedure several biases can influence the results. By arranging yourmeasuring procedure in a proper way, it is possible to avoid most of these biases. Still loudnessmatching is a difficult task and therefore we have developed a new procedure that should make it lessdemanding for the subject.

09.45 – 10.00 Finn Dubbelboer – Intelligibility of speech in noise after digital processingUnderstanding speech in a noisy environment is often difficult for hearing impaired persons.Traditional hearing aids cannot solve this problem since amplification of the input signal affects bothspeech and noise. Historically, the introduction of digital hearing aids provided a basis forsophisticated signal processing such as noise suppression. A well-known method in this respect is“spectral subtraction” which improves signal-to-noise ratios by subtracting the estimated (average)noise level in a number of bands from the input-signal. Unfortunately, speech intelligibility is not


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improved after this operation due to processing-related artifacts. Current studies with normal hearingpersons showed that a new version of “spectral subtraction” involving a different amount ofsubtracted energy and additional temporal smoothing, slightly improves intelligibility.

10.00 - 10.15 Koen Rhebergen - Prediction of the speech intelligibility under maskingconditions

The perception of speech can be difficult due to masking by a concurrent background noise. Hereby,not all speech information is available, such that the listener may be unable to understand the messageeasily. To predict the speech intelligibility under masking conditions, a method has been developed tocalculate the audibility of speech with respect to the redundancy of the speech message. The outcomeof the method is the so-called Speech Intelligibility Index (or SII). The SII is calculated from thespeech spectrum, the masking noise spectrum and the hearing threshold of the listener. The audiblepart of the speech spectrum is determined, frequency weighted, and summed across frequency toobtain the SII or the proportion of speech information that is available to the listener. An SII of zeroor unity indicates that no speech information or all speech information is available, respectively.A conventional measure indicative for the capacity of a listener to understand speech in a competingbackground noise is the so-called Speech Reception Threshold (or SRT). The SRT is equal to theSNR needed for 50% sentence intelligibility. Normal hearing requires a SRT in stationary speech-shaped noise of –5 dB, which corresponds to an SII of 0.33. This means that if 33% of the speechmaterial is audible for the listener, 50% of the sentences is correctly understood. With the SII model,thresholds in stationary noise can be very well described. However, the SII model does not take intoaccount any fluctuations in the masking noise. Hence, the model will yield similar SII values,regardless of the degree of fluctuation. In contrast, from the literature it is clear that the normalhearing perform better in fluctuating noise conditions compared to steady state noise conditions of thesame level and amplitude spectrum. Thus, thresholds for speech intelligibility in fluctuating noisecannot be predicted well by the SII model. Since most real-life noises do exhibit strong intensityvariations over time or frequency, there is a great interest in an adequate procedure to predict speechintelligibility in interfering real life noises.The present paper describes an SII-based approach to model SRTs determined in fluctuating noise.The basic principle of this approach is that both speech and noise signal are partitioned into smalltime frames. Within each time frame, the SII is determined, yielding the speech information availableto the listener at that time frame. Next, the SII values of these time frames are averaged, resulting inthe SII for that particular noise type. From the literature as well as form experiments in ourlaboratory, many SRT values are available for a variety of noise types. It will be shown that thisapproach can give a good account for the existing data.

10.15 - 10.30 Gaston Hilkhuysen - Clinical measurement of spectral and temporal resolutions inhearing

Many hearing impaired (HI) experience difficulties understanding speech, especially in the presenceof concurrent noise. An elevated hearing threshold can explain part of these difficulties as mereamplification of speech and noise, to compensate for these elevated thresholds, improves speechintelligibility. But most HI still perform less well then normal hearing (NH). Some HI fail tocomprehend speech in noise even when these are at a different frequencies or moments in time, i.e.they suffer from reduced spectral and/or temporal resolutions, respectively. Classical measurementsof spectral and temporal resolutions requires intensive training of listeners, making theminappropriate for clinical settings. We measure spectral and temporal resolutions in a way apt fornaïve listeners. Both tests use the same signal, a sweep that raises in frequency within a fixed period.A masking noise has either a spectral or temporal gap whose size at the detection threshold revealsthe spectral or temporal resolutions. Before applying these tests to HI, NH are tested under a varietyof conditions to verify that test results are in accordance with theory on spectral and temporalresolutions.

Session 4 (Moderator: Guido Smoorenburg)

11.00 – 11.15 Ignace Hooge - Introduction: cycling to the Uithof from home11.15 – 11.30 Ryota Kanai - Offset signals of visual object trigger perceptual fading11.30 – 11.45 Christiaan Paffen - Binocular rivalry between moving stimuli: the effect of surround

motion.11.45 – 12.00 Mark Nieuwenstein - Temporal limitations in conscious visual perception reflect

attentional inertia


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12.00 – 12.15 Jan Souman - A 2D-model of motion perception during smooth pursuit eyemovements.

11.00 – 11.15 Ignace Hooge - Cycling to the Uithof from homeWhen cycling from the "van den Boschstraat" to the "Uithof", one has to go through the crowdedcenter of Utrecht. To be able to perform this difficult task different types of information have to beprocessed by the brain. In this talk I will use examples from my daily cycling tour to introduce boththe PhD-students of the vision-group of Psychonomics and their research topics. Because cycling inheavy traffic is very difficult, topics such as: visuo-motor learning, low-level motion detection, visualsearch, attention, working memory, awareness and (compensation for) eye movements will beelaborated upon.

11.15 – 11.30 Ryota Kanai - Offset signals of visual object trigger perceptual fading (co-authors: Y. Kamitani & Frans Verstraten)

After prolonged fixation, a stationary object placed in the periphery fades and disappears from ourvisual awareness (the Troxler effect). Previously, we have shown that such fading is triggered, in atime-locked manner, by visual transients such as additional visual stimuli flashed near the object,apparent motion, and a brief disappearance of the object itself (Kanai & Kamitani, J. Cog. Neurosci.in press). Because each of these stimuli contain both onset and offset components, we furtherexplored whether the onset or offset transient is critical for the fading induction. We used fivestimulus conditions to dissociate their effects. In all the conditions, the target object (a red disk on anear- isoluminant green background) was continuously present for the entire trial (2082 ms). 1) Awhite ring was flashed for 118 ms in the middle of the trial (flash condition). 2.) A white ringappeared in the middle of the trial and remained on until the end (onset condition). 3.) A white ringwas present from the beginning of the trial and disappeared in the middle of the trial (offsetcondition). 4.) No ring was presented. (control condition A). 5.) Both the target disk and the ring werepresented continuously for the full duration of the trial (control condition B). Fading was inducedonly in the flash condition and the offset condition, and the strength of the effect did not differbetween these two conditions. The onset condition did not induce the fading effect any larger than thecontrol conditions. These results indicate that the critical factor for the transient-induced perceptualfading is the offset signal of an object. Such offset signals may provide a reset signal for the visualsystem and facilitate the processing of subsequent stimuli.

11.30 – 11.45 Christiaan Paffen - Binocular rivalry between moving stimuli: the effect ofsurround motion (co-authors: Ryota Kanai, Susan te Pas & Frans Verstraten)

When two dissimilar stimuli are presented dichoptically, the percept generally alternates between thetwo monocular stimuli; a phenomenon known as binocular rivalry. The dominance of a specificpercept during rivalry can be affected by a surrounding stimulus. For example, if two discs containingbars with orthogonal orientations are both surrounded by an annulus containing bars with the sameorientation as one of the two discs, the disc containing the bars orthogonal to the surround is moredominant (Fukuda & Blake, 1992). Here, we investigate whether this preference for a stimulusdeviant from its surround can also be observed for moving stimuli.Stimuli: Two discs containing vertical sine-wave gratings, always moving horizontally in oppositedirection, were presented dichoptically at the center of fixation. The discs could each be surroundedby an annulus containing a vertical sine-wave grating moving in the same direction as one of the twodiscs. The annulus was either presented to one eye [one-eye condition] or both eyes [two-eyescondition]. In the two-eyes condition, the annuli moved in the same direction. In the one-eyecondition, the grating in the annulus moved in the same direction as the grating in the disc in the sameeye, or in the same direction as the grating in the disc presented to the other eye. Observers had tocontinuously indicate the perceived direction of motion in the center disc.Results: For both conditions, the disc containing the grating with a direction of motion opposite to thesurround was more dominant. Most interestingly, for the one-eye condition, the disc containing thegrating moving in the direction opposite to the motion in the annulus was more dominant, irrespectiveof its positioning (same or different eye as compared to the annulus). Thus, also during binocularrivalry of moving stimuli, the grating in the disc moving in the deviant direction, as compared to themotion direction in the annuli, is preferred.

11.45 – 12.00 Mark Nieuwenstein - Temporal limitations in conscious visual perception reflectattentional inertia (co-authors: Ignace Hooge & Rob van der Lubbe)


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When two visual targets (T1 and T2) are presented within 200-400 ms in a rapid serial visualpresentation (RSVP) sequence of distractors, observers have great difficulty in reporting the identityof the second target. This phenomenon called the attentional blink (AB) is typically assumed to reflectthe slow and capacity limited nature of consolidating visual stimuli into reportable memory traces. Inparticular, the idea is that during consolidation of T1, T2 is likely to be overwritten by subsequentlypresented distractors before it can access consolidation.In the present study, we show that the AB effect can be substantially reduced when T2 is preceded bya distractor that captures attention either because it pops-out, or, because it shares a target-definingfeature. Importantly, the observed increase in T2 performance did not occur at the expense of T1performance. In contrast to extant models of the AB, these findings suggests that T2 can engageconsolidation without hindering the ongoing consolidation of T1. In addition, the finding that the ABwas attenuated when T2 was preceded by a distractor that captured attention suggests that the ABmight reflect inertia in selecting new elements.

12.00 – 12.15 Jan Souman - A 2D-model of motion perception during smooth pursuit eyemovements (co-author: Alexander H. Wertheim)

During ocular pursuit of a moving target the retinal image velocity of other objects in the visual fielddiffers from their physical velocity. To produce veridical perception of the motion of these objects thevisual system has to compensate for the eye movements. When an object is moving colinearly withthe pursuit target, compensation occurs, although incompletely. This partial compensation producesillusions like the Filehne illusion and the Aubert-Fleischl phenomenon. However, whether the visualsystem compensates for eye movements when an object moves non-colinearly with the pursuit targetis still a matter of debate. We investigated whether compensation occurs in the noncolinear case andwhether it is the same as for colinear motion.We measured the perceived motion direction of a moving dot during ocular pursuit (10°/s) of ahorizontally moving pursuit target. The angle of the physical motion path of the dot relative to thepursuit path was varied from 0° to 360°. We found that observers made systematic errors in indicatingthe motion direction. The pattern of these errors was different for a dot moving with a lower (3°/s)than with a higher (8°/s) speed, with larger errors for the lower speed. The data can be explained by amodel that assumes that compensation for eye movements is independent of speed and direction ofthe moving dot. Compensation is assumed to be normally distributed, with mean and standarddeviation varying between observers.

Session 5 (Moderator: Raymond van Ee)

14.00 – 14.15 Jack van Honk - The neurobiology of emotion14.15 – 14.30 Dennis Schutter - A functional connectivity model of depression14.30 – 14.45 Peter Putman - Reflexive orienting in response to emotional eye gaze14.45 – 15.00 Erno Hermans - Central effects of testosterone on emotional processing as measured

by fMRI

14.00 – 14.15 Jack van Honk - The neurobiology of emotionResearch in the area of human emotion was until recently mainly limited to the cognitivepsychological domain. Emotional processing was described functionally and scarce reference wasmade to how processing might be instantiated in the brain. Currently, emotion research receivesincreasingly more attention from areas such as neurophysiology, neurochemistry and neuroanatomy,leading to the development of a new discipline: Affective Neuroscience. “Human” AffectiveNeuroscience concentrates on showing correlations between brain activity and emotional behaviorusing PET and fMRI, thus causal connections in this field have scarcely been established. We aim toestablish such causal relations between the human brain and approach and withdrawal-relatedemotion. Approach and withdrawal is in simple animals primarily illustrated by the classic fight-flightresponse, which is largely initiated in limbic affective circuits and modulated by hormones such ascortisol and testosterone In humans, approach and withdrawal are rudimentary to the evolvement ofthe emotions anger and anxiety. These occur in the behavioral hiatus when actions are delayed andprovide for more flexible behavioral tendencies wherein the cerebral cortex is strongly implicated.The left and the right dorsolateral prefrontal cortices would respectively be involved in consciouslycontrolled (and thus more sophisticated forms) of behavioral approach and withdrawal. Nevertheless,a subcortical affective shortcut, the thalamic-amygdala pathway is argued to still be functional inhumans and would provide for the biologically prepared emotional response, unconfounded by thewhims of consciousness. Finally, the orbitofrontal cortex bears strong afferent and efferent


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connections with cortical and subcortical brain structures, and is suggested to act as an affectivecontrol and relay station. Hypothesizing from this neurobiologically constraint model we aim toinvestigate approach and withdrawal-related emotion in terms of emotional perception, emotionalmemory, and attentional and physiological responses to emotional stimuli. We will scrutinize the roleof the steroid hormones cortisol, testosterone and dehydroepiandrosterone (DHEA) and the role of thestructures of the cerebral cortex implicated in emotional behavior (i.e. dorsolateral prefrontal,orbitofrontal, parietal, temporal and occipital). Causal relations are intended to be established byexploiting our expertise with controlled hormone administrations and repetitive transcranial magneticstimulation (rTMS), and combining these with the brain imaging techniques EEG/ERP and fMRI.

14.15 – 14.30 Dennis Schutter - A functional connectivity model of depressionIt is argued that clinical depression goes accompanied by reductions in cortical excitability of the leftprefrontal cortex (PFC). In agreement, a method capable of enhancing cortical excitability, repetitivetranscranial magnetic stimulation (rTMS), when applied over the left PFC has shown to exhibitantidepressant efficacy, although the overall therapeutic effects remain inconclusive. The cerebralpathophysiology of depression is however not limited to dysfunctions in the PFC. Presently, the roleof rTMS over the PFC in the treatment of depression as well as recent research in the field ofaffective neuroscience investigating the antidepressant effects of rTMS over other brain regions willbe discussed. Evidence from EEG, endocrinological and lesion studies suggests the involvement ofthe parietal cortex and the cerebellum as well as abnormalities in functional connectivity indepression. Moreover, rTMS applied over both the parietal cortex and the cerebellum have shown toexhibit antidepressant properties. Based on these recent findings an rTMS-oriented functionalconnectivity model of depression will be presented.

14.30 – 14.45 Peter Putman - Reflexive orienting in response to emotional eye gazeNormally, centrally presented symbolic cues are capable of inducing orienting of attention in a spatialcueing design only at longer presentation times and when it is strategically efficient to accept the cuesas generally valid. Centrally presented pictures of human faces that naturalistically provide suchspatial cues by head orientation or eye gaze, seem capable of inducing fast and reflexive orientingreminiscent of classical exogenous cueing. The present studies further investigated this extraordinarycharacteristic of face-stimuli and scrutinized the interaction between this cueing mechanism andemotional expression of the cueing faces.

14.45 – 15.00 Erno Hermans - Central effects of testosterone on emotional processing asmeasured by fMRI (co-authors: Adriaan Tuiten, Jack van Honk, & Nick Ramsey)

As part of a wider project investigating central effects of steroid hormones, the present study testedeffects of testosterone on brain areas involved in sexual arousal. During three separate sessions,twelve healthy female subjects were scanned using functional Magnetic Resonance Imaging whilewatching erotic film excerpts. The first session was used to explore and specify regions of interestinvolved in sexual arousal. During a second and third session, subjects watched similar films in aplacebo controlled crossover design testing the influence of a single dose of testosterone in these pre-specified regions. Replicating previous work, additional self-report questionnaires indicated thatindeed testosterone increased sexual arousal provoked by erotic film excerpts. Functional MRI resultsshowed that these effects were accompanied by augmented activity mainly in dorsolateral prefrontal,thalamic and septal areas, whereas amygdala activity dropped under testosterone. The putative rolesof these areas in sexual arousal will be discussed in relation to animal models.

Session 6 (Moderator: Astrid Kappers)

15.30 – 15.45 Byung-Geun Khang - Perception of illumination direction in 3-D shaded image15.45 – 16.00 Michelle Doumen - Visual space under free viewing conditions16.00 – 16.15 Sander Zuidhoek - Haptic space: the role of visual processing16.15 – 16.30 Matthijs Noordzij - The influence of perspective on the properties of spatial mental

models of blind and sighted people

15.30 – 15.45 Byung-Geun Khang - Perception of the direction of illumination in images ofdiffering surface materials under different light fields (Co-authors Jan Koenderink& Astrid Kappers)

Shading of 3-D objects refers to variations in luminance or color as a function of the angle of theillumination direction with respect to the surface. Shading elicits a compelling sense of shape,illumination and surface properties. However, it is not yet certain how this is achieved. Not only the


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surface orientation but also the surface material and illumination properties contribute together to theformation of a shading image. The majority of the studies about shading concerns shape fromshading. We, however, used an illuminant direction matching procedure to examine how well humanobservers can estimate the direction of illumination in images of 3-D shapes of differing materialsurfaces in different light fields. In experiment 1 stimuli were renderings of a dodecahedron and asphere projected orthographically and juxtaposed on a CRT screen. Two lighting modes (collimatedand hemispherical diffuse lighting), twenty-six illuminant directions (differing in azimuth and phaseangle) and perfectly diffuse reflectance with albedo 0.5 were used to render the faces of the twostimuli. At the start of each trial, the two stimuli were presented with different directions ofillumination. Observers adjusted the direction of illumination on the sphere to match the direction ofillumination on the dodecahedron. No systematic difference in matched directions between the twolighting conditions was found. No difference between azimuthal directions but significant differencesbetween elevation angle directions were found; frontal directions were matched less precisely thanrear directions. In experiment 2, stimuli were two spheres presented in the centers of the two halves ofa CRT screen. Four different types of BRDFs, representing diffuse scattering, specular scattering,backscattering and asperity scattering, two lighting modes (collimated and hemispherical diffuse) and25 test lighting directions were used to render the surface of the two spheres. Significantly greaterdeviations were made in matched directions under hemispherical diffuse than collimated lightingconditions. Frontal test directions tended to produce more discrepancies in matching than rear testdirections (except one case of backscattering under the collimated lighting condition). As aconclusion, estimation of the direction of illumination in shaded images (without cast shadows)depends on type of material surface (BRDFs) and light field.

15.45 – 16.00 Michelle Doumen - Visual space under free viewing conditions (Co-authors AstridKappers & Jan Koenderink)

Research on the perception of visual space is mainly done under very restricted conditions,completely dark rooms, head of the observer fixated etc. Under these conditions, visual space isdeformed as compared to physical space i.e. the actual lay-out of the world around the observer. Weare interested in whether this deformation is still present under less reduced circumstances. Inexperiments done so far we had observers seated on a chair without a chinrest in an empty officeroom with artificial light. Under these conditions large deviations from veridical settings were foundwhen the observer had to direct a pointer to a target (a sphere). The size of these deviations wasdependent on the distance between the two objects and the ratio of the distance between the objectsand the observer. The pattern of deviations found were very similar to the pattern found for the sametasks in an environment with less depth-information present.A next step in this project will be to change the context, for example covering the walls with patternsof lines or dots, and see whether this has an effect on the deviations. Apart from that, we are planningto do experiments in a 3D layout.

16.00 – 16.15 Sander Zuidhoek - Haptic space: the role of visual processing (co-authors: AstridKappers, Matthijs Noordzij & Albert Postma).

Systematic deviations occur when blindfolded subjects set bars parallel in the horizontal plane, usinghaptic information (e.g. Kappers and Koenderink, 1999). The deviation patterns reflect theemployment of a cognitive, allocentric framework and an implicit egocentric one biasingperformance. Recently, we have shown that a 10 seconds delay between perception of a reference barand the parallel-setting of a test bar improves performance (Zuidhoek et al., 2003), implying a shiftfrom egocentric towards more allocentric representation during the delay. Our latest work suggests aprominent role of visual processing in the allocentric (re)coding of haptic information. In the currenttalk, the contribution of visual imagery, visual attention and visual experience to haptic spatialperformance will be discussed.

16.15 – 16.30 Matthijs Noordzij - The influence of perspective on the properties of spatialmental models of blind and sighted people (co-authors Sander Zuidhoek & AlbertPostma)

Descriptions with a route perspective take the addressee into the environment and give information onposition of objects relative to the changing position of the addressee. In contrast, descriptions with asurvey perspective adopt a birds-eye view and describe objects with respect to one another. Aninteresting question is to what extent the description perspective has an influence on the features ofthe spatial representation (spatial mental model). We studied the characteristics of the mental modelsthat were constructed from route or survey descriptions with several tasks, among which a


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recognition/priming task and a bird-flight distance comparison task. Spatial priming and symbolicdistance effects were present after sighted and blind participants had studied a verbal description.Sighted individuals seemed to form the same spatial mental models from route and surveydescriptions. Blind individuals performed similar to sighted participants after studying a routedescription, but they performed worse than sighted participants after studying a survey description.Therefore, route and survey descriptions can be converted into spatial mental models, whichincorporate distance information. However, blind individuals might construct a spatial mental modelmore effectively from a route than a survey description.


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Evening Program Tuesday

Keynote-Lecture 2 (Moderator: Jan Koenderink)

20.00 – 21.00 TOWARDS COMPLETE MODELS OF HUMAN VISUAL-MOTORBEHAVIORSINVITED LECTURE BY PROFESSOR DANA BALLARD(Universtiy of Rochester, New York, USA)

Most models of human vision have been specialized to sub-modalities of vision and tested in limitedvisual domains. One of the main reasons for this conservatism has been the lack of appropriatecomputing power and attendant software data structures to model the complexity of the everydayworld. However recently, the steady increase in computing power has been augmented with a set ofsoftware packages for rendering of realistic figures in complex environments. As a consequenceresearchers have begun to develop and test models that try and tackle more of the full complexity ofhuman vision as used in behaviors. Examples of this are the early work with the avatar “Jack” at theuniversity of Pennsylvania and the fish animats developed by Terzopoulos at the university ofToronto. Our graphics environment at Rochester uses the DI-guy animats developed by BostonDynamics together with Vortex physics simulator for physical collisions. Together these packagescomprise a human model that can act in a reasonably complex world. Our research program isdirected towards designing and implementing visuo-motor behaviors for these animats that haveproperties which can be compared to those exhibited by real humans acting in comparable realenvironments. One of the main results of this research is to demonstrate the need for a computationalhierarchy. Such a hierarchy is a natural consequence of visuo-motor behavior, which exhibits manydifferent modeling problems at different temporal scales. We motivate our particular hierarchythrough examples developed with the animats.


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Wednesday 25 JUNE

Session 7 (Moderator: Roy Kessels)

08.45 – 09.00 Hans van der Steen – Research in Rotterdam (Eli Brenner)09.00 – 09.15 Gerben Rotman – Eye orientation information for localising visible stuctures etc.09.15 – 09.30 Denise de Grave – The Ebbinghaus figure is more than a size illusion09.30 – 09.45 Jeroen Granzier – Color induction

08.45 – 09.00 Hans van der Steen – Research in Rotterdam (Eli Brenner)Our group is interested in the relationships between eye and body movements and perception. We areinterested both in the way perception influences action and in the way our actions influenceperception. We examine these issues in healthy humans, selected patient populations, and in animals.We hope to determine which aspects of our sensory stimulation drive our movements, how they doso, and how these (eye) movements influence subsequent sensory stimulation. In my presentation Iwill dwell on some of the most promising new findings and approaches.

09.00 – 09.15 Gerben Rotman - Eye orientation information for localising visible stuctures etc.In daily life we often have to localise objects while our eyes are moving, either because we arelooking at a moving object or because we ourselves are moving. Smooth eye movement generallymake the retinal component of localisation much simpler, because their purpose is to stabilise theobject's image on the retina. However, the localisation depends on information about the orientationof the eye. The way in which this occurs has been the topic of much debate for many years. The mostconsistent finding within this debate is that subjects misjudge the position of flashed targets in thedirection in which their eyes are moving. We examined this phenomenon in more detail, and showthat the mislocalisation is in the direction in which the eye moves after the target has been presented.

09.15 – 09.30 Denise de Grave – The Ebbinghaus figure is more than a size illusion. (co-authorsMarianne Biegstraaten, Eli Brenner & Jeroen Smeets)

The effect of circular flankers on judgements of the size of a central disk is known as the Ebbinghausillusion. Since the work of Aglioti et al. (1995) there is a debate on how to interpret the small effect ofthe flankers on prehension. Franz et al (2003) suggested that the same visual information isresponsible for the perceptual judgements of size and for the effects on grip aperture. Othersinterpreted the effect on grip aperture as caused by other mechanisms, such as obstacle avoidance(Haffenden & Goodale, 2000; Smeets et al., 2003). If the latter interpretation is correct, the effect ofthe Ebbinghaus illusion on prehension will depend on the positions of the flankers relative to themovement of the digits. The effect on size judgements should be independent of the exact flankerpositions.To distinguish between the two interpretations, we used a display consisting of a central disk (varyingin size) surrounded by four large or small flankers. The array of flankers could be rotated by 45°. Inthe first part of the experiment subjects had to grasp the central disk. In the second part of theexperiment they had to make a perceptual judgement of the size of the central disk.For perceptual judgements, the effect of the size of the flankers was independent of their position. Ingrasping, the final grip orientation and movement time showed an effect of the position of theflankers. We conclude that the effect of the flankers on prehension is due to their interference with themovement (they act as obstacle or distractor), and not due to the misjudgment of the central disk'ssize.

09.30 – 09.45 Jeroen Granzier - Color inductionThe main unresolved issue in colour research is the phenomenon of ‘colour constancy’. Colourconstancy is the ability to perceive object colours as fairly constant, despite considerable changes inthe spectral composition of the illuminant. The main question is how the visual system recovers thecolour of an object, considering that the spectral distribution of the light emanated from that object isthe product of Illumination and Reflectance. The visual system has to disentangle these two elementsby considering the chromatic context in which the object is seen. Chromatic induction is the change inperceived colour that is caused by considering the surrounding surfaces.I will describe three related experiments about colour induction. The same seven subjects took part inall three experiments. The stimuli were presented on a calibrated high-resolution RGB monitor.Before each experiment subjects dark-adapted for 10 minutes. They then made 20 settings for each of


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4 background conditions. Each background consisted of a random pattern of red and green squares.The 80 trials were presented in random order. Two of the background conditions had the same ratiosof l-m cone stimulation, but in one case the average luminance of the green squares was higher, whilein the other that of the red squares was higher. This meant that there was more stimulation of l coneswhen the red squares were brighter, and of m cones when the green squares were brighter. The othertwo conditions had the same average stimulation of each type of cone, but again either the luminanceof the green squares or that of the red squares was higher (the darker squares were now moresaturated).In the first two experiments subjects were asked to set a central circle to appear to be a neutral grey(by 'moving' within an isoluminant colour space). In the first experiment, the circle's luminance wasbetween that of the light and dark surrounding squares. Subjects systematically set the target circle to“greener” values, implying that they see the target circle as ‘redder’, whenever the luminance of thegreen squares in the surrounding was higher. This is consistent with the proposal that the correlationbetween the luminance and colour distribution in the scene is used to derive the colour of theillumination. However, similar results were found in the second experiment, which was identical tothe first except that the luminance of the target circle was 50% higher, so that the target circle wasbrighter than any field in the background. In the third experiment we presented the pairs ofbackground conditions in which either the red or the green surfaces were brighter simultaneouslyrather than on separate trials. A standard grey circle was presented on the background on the left. Theobserver’s task was to match its appearance by manipulating the chromaticity (red-green dimension)and luminance (high-low) of a test circle that was presented on the background on the right. Againthere were four conditions, because either the l-m cone ratios or the average stimulation of each conetype could be matched, and in each case the red squares could either be bright on the left or on theright. Rather than the two kinds of backgrounds cancelling each other we found that colour inductionwas primarily determined by the brighter squares in the immediate vicinity of the target. Thusalthough the way the illuminant influences the correlation between the luminance and colourdistribution in the scene may be the basis for these results, it is unlikely that such a correlation isactually used to estimate the chromaticity of the illuminant.

Session 8 (Moderator: Maarten Frens)

09.55 – 10.10 Marianne Biegstraaten - Müller-Lyer and grasping: Illusion or obstacles?10.10 – 10.25 Dorien Rijkaard - Cervico-Ocular-Reflex adaptation10.25 – 10.40 Beerend Winkelman - The complex spike code

09.55 – 10.10 Marianne Biegstraaten – Müller-Lyer and grasping: Illusion or obstacles? (co-autors Denise de Grave, Eli Brenner & Jeroen Smeets)

The influence of the Ebbinghaus illusion on grasping has been attributed to the surrounding circlesbeing considered as obstacles (Haffenden & Goodale, 2000). However, this view is controversial. Weexamined whether we could verify this view using the Müller-Lyer illusion. With the Müller-Lyer,whether the fins act as an obstacle should depend on the direction of approach. When coming fromthe side both digits "have to" avoid the fins of the figure. When coming from below the figure theindex finger has to avoid the fins, but the thumb has not. We let subjects grasp a bar which wassuperimposed over the shaft of a vertically placed Müller-Lyer illusion. The bar had to be graspedeither from a starting position below the figure or from one to the right side of the figure. The graspswere analysed in terms of the trajectories of the individual digits. The results showed an effect of theillusion on the deviation of the index finger regardless of the starting position. For the thumb wefound a different effect of the illusion depending on the starting position. We conclude that illusionscan induce changes in motor strategy which are unrelated with the spatial attributes the illusion issupposed to change.

10.10 – 10.25 Dorien Rijkaard - Cervico-Ocular-Reflex adaptationIn daily life the COR works in conjunction with the Vestibulo-Ocular reflex (VOR) and theOptokinetic reflex (OKR) in order to prevent visual slip over the retina during head movement. TheVOR gain can be adapted by inducing a mismatch between the visual and vestibular information. TheCOR follows the same pathways as the VOR and the COR reacts to neck-proprioception. That is whyit is a legitimate question if the COR gain can be adapted by inducing a mismatch between visual andneck-proprioception. So far, there has been no investigation on the effect of adaptive plasticity of theCOR. In the present study 13 healthy subjects were rotated in the dark in a trunk-to-head manner (thehead fixed in spaced with the body passively rotated under it at peak velocity of 1,3°/s) under


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adaptive conditions. Position of the eyes was recorded with an infrared recording technique. Wefound that the COR-gain can adapt after only 10 minutes of stimulation.

10.25 – 10.40 Beerend Winkelman – The complex spike codeComplex spikes are action potentials of cerebellar Purkinje cells that are caused by input from theInferior Olivary nucleus. These powerful depolarizations are able to induce plastic changes in thePurkinje cell synaptic input and have attained a prominent place in cerebellar learning theories.Floccular complex spikes are believed to carry a pure sensory signal, slip of the retinal image, whichaids as an error signal in training the cerebellum to drive compensatory eye movements. In practicehowever, slip is highly correlated with eye movement, which is a motor signal. In our study we triedto tackle the assumption that the Floccular complex spikes are coding only retinal slip. By breakingup the relation between slip and eye movement using high frequency noise as an optokinetic stimuluswe could study the components of the signal in relative isolation. Our study shows that an efferencecopy signal of eye movement additionally modulates Floccular complex spikes. This supports thenotion of the complex spike code as a genuine sensory-motor signal.

Session 9 (Moderator: Martine van Zandvoort)

11.00 – 11.15 Richard van Wezel - Motion processing in cortical areas MT and MST11.15 – 11.30 Janos Perge - Direction tuning of macaque MT neurons: a reverse correlation study11.30 – 11.45 Roger Bours - Speed tuning of neurons in macaque MT11.45 – 12.00 Jeanette Lorteije - Implied motion in macaque area MT and MST12.00 – 12.15 Jaap Beintema - Rivalry in biological motion

11.00 – 11.15 Richard van Wezel - Motion processing in cortical areas MT and MSTBoth in human and non-human primates cortical areas MT and MST play a crucial role in processingof visual motion information. Neurons in these cortical areas respond vigorously when a pattern ismoving in their receptive fields. The responses are directionally selective, which means that theneurons have one preferred direction and an opposite null direction. Furthermore, these neurons areaffected by higher cognitive information, like attention and object recognition. In our lab weinvestigate bottom-up questions, like the mechanisms of directional and speed selectivity, the spatialstructure of MT/MST receptive fields and the relationship with psychophysical studies on motionperception. We also investigate top-down questions, like the role of these cortical areas in perceptionof implied motion (static pictures of moving objects) and biological motion.

11.15 – 11.30 Janos Perge - Direction tuning of macaque MT neurons: a reverse correlationstudy (co-authors: Bart Borghuis, Martin Lankheet & Richard van Wezel)

We measured the time course of direction tuning of motion sensitive neurons in macaque area MT. Arandom dot pattern was positioned over the receptive field and it was shifted with a certain step size atfixed time intervals (8-26 msec) pseudo-randomly in 8 different directions. This created a sequence ofmotion impulses in different directions. Spike trains of the neurons were recorded and reverse-correlated to the stimulus sequence. This allowed us to reconstruct the time course of direction tuning.The results show that in 41% (n = 114) of the MT cells temporal response profiles are biphasic with apeak at the response latency (45-75 msec) and a rebound at longer delays (60-120 msec). Furtheranalysis reveals that the impulse response is modulated by preceding motion impulses, suggestingnon-linear mechanisms. The response to any direction is higher if the preceding motion impulse wasto the null direction while it is lower if the preceding motion impulse was to the preferred direction(short term adaptation). Computer simulations show that this phenomenon leads to the biphasictemporal response profile. Moreover the modulation strength is highest at a median of 34 msec andchanges with step size. These results are in line with previous work related to short term adaptation(Priebe et al., 2002) and suggest a local cortical circuit with inhibitory interactions between similarlytuned MT neurons.

11.30 – 11.45 Roger Bours - Speed tuning of neurons in macaque MT (co-authors: Richard vanWezel and Martin Lankheet)We investigated low-level mechanisms of speed perception in macaque area MT, using a motionreverse correlation technique. We were specifically interested in the temporal dynamics of velocitytuning, the contribution of different combinations of spatial displacement and temporal delay, andtheir interactions.A random dot pattern was positioned over the receptive field and it was shifted at a constant rate, butwith a pseudo random sequence of different step-sizes (0.04-1.2deg), in the neuron’s preferred and


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null direction. This created a random sequence of motion impulses with variable step size, inopposing directions. The neuron's response in the form of a spike train was recorded and reverse-correlated with the stimulus sequence. This allows us to reconstruct the time course of tuning for stepsize. A comparison of such results for different temporal delays, different pixel sizes and contrastswill allow us to characterize the temporal dynamics underlying velocity tuning. Preliminary resultsfor the different types of measurements will be discussed.

11.45 – 12.00 Jeanette Lorteije - Implied motion in macaque area MT and MSTHuman fMRI studies have shown that static pictures of objects in motion (such as running athletesand falling objects) can increase activation of the human analogue of medial temporal and medialsuperior temporal cortex (MT/MST complex). Viewing pictures without implied motion (for instancepeople sitting or houses) does not evoke this response (Kourtzi & Kanwisher, 2000; Senior et al.,2000). To know more about the time course and direction selectivity of activation by implied motionwe recorded single cells in macaque areas MT and MST. While the animal is fixating, pictures ofpeople and monkeys running or standing still are presented in the receptive field of the cell. So far noevidence is found for direct activation of MT cells by implied motion. Recent recordings howeversuggest that some cells in MST do respond more to pictures of running people then to pictures ofpeople standing still. Responses are correlated with the preferred direction to real motion (random dotpatterns). The initial response at about 90 milliseconds is roughly the same for all pictures. However,we observe a difference in response between pictures with implied motion in preferred directionversus not preferred and without implied motion peaks after about 200 msec. and remains until theend of the stimulus presentation (1 second). This delay suggests that activation of MST by impliedmotion is a top down process from object selective neurons as found in macaque temporal cortex. Tofurther investigate the temporal properties of activation by implied motion and to extrapolate acrossspecies, data from this experiment will be compared with data from a human EEG experiment usingthe same stimuli.

12.00 – 12.15 Jaap Beintema – Rivalry in biological motionPeople can surprisingly well recognise the complex movement patterns that can arise from humanlimb movement. Monkey and human brain studies suggest the brain has areas that specifically mayencode biological movements. We aim to probe the strength of biological movement representationsunder conditions of binocular rivalry. We find that when each eye is presented a different point-lightwalker, differing in at least color and phase of the walking cycle, the percept alternates. We presentpreliminary data and discuss whether these perceptual alternations reflect rivalry at the level ofbiological motion representation or at lower levels.

Session 10 (Moderator: Frans Verstraten)

14.00 – 15.00 Discussion & Wrap up.


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prof.dr. e.h.f. de haan utrecht university · prof.dr. d. ballard university of rochester, usa...

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