proceedings of the 4 helmholtz retreat...proceedings of the fourth helmholtz retreat 13-15 june 2007...

Proceedings ofProceedings of the 4the 4 thth Helmholtz Helmholtz RetreatRetreat

13-15 June 2007 Bergen, the Netherlands

Proceedings of the Fourth Helmholtz Retreat 13-15 June 2007

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Scientific director Prof.dr. Albert V. van den Berg Utrecht University Members of the board Prof.dr. Johan .J. Bolhuis Utrecht University Prof.dr.ir. W.A. Dreschler University of Amsterdam Prof.dr. Casper J. Erkelens Utrecht University Prof. Dr.Ir. Joost M. Festen Free University Amsterdam Prof. Dr. Maarten Frens Erasmus University Rotterdam Prof.dr. Edward H.F. de Haan Utrecht University Prof.dr. Jan J. Koenderink Utrecht University Prof. dr. Leon .J. Kenemans Utrecht University Dr. Hans van der Steen Erasmus University Rotterdam Dr. H. Verschuure Erasmus University Rotterdam Prof.dr. Frans A.J. Verstraten [chair] Utrecht University Scientific advisory council Prof.dr. Dana Ballard University of Rochester, USA Prof.dr. Alain Berthoz College de France, Paris, France Prof.dr. Heinrich Bülthof Max Planck Institute for Biological Cybernetics, Tübingen, Germany Prof.dr. J.J. Eggermont University of Calgary, Canada Prof.dr. A.D. Milner University of Durham, UK Prof.dr. Charles M.M. de Weert Radboud University Nijmegen, The Netherlands Education committee Dr. Martin Lankheet Utrecht University Dr. Maarten van der Smagt Utrecht University Prof. Dr. Jeroen Smeets Free University Amsterdam Prof. Dr. Ir. Joost Festen Free University Amstrerdam Dr. Raymond van Ee Utrecht University Office management Mrs. Veronica Maassen-Monrooij Utrecht University

Special thanks to Veronica Maassen-Monrooij,

Titia Gebuis & Ans Horchner


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Proceedings of the Fourth Helmholtz Retreat

13-15 June 2007

Bergen The Netherlands

Organiser

Frans Verstraten


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Contents Welcome 5 Our keynote speakers 6 List of participants 7 Program in the fast lane 10 Program & Abstracts

Wednesday 13

Thursday 17

Friday 23 Poster Abstracts 26


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Welcome… Dear participants of our Helmholtz School retreat, Our bi-annual meeting, here in Bergen, already has become somewhat of a tradition. A tradition to be cherished, because it is the best event to obtain an overview of the entire school’s activities, to learn from your colleagues what fires their scientific imagination, and to enjoy the Community that the Helmholtz School aims to be. May 15, 1992, was the date that the four founders of the Utrecht Institute of Biophysics initiated the establishment of a Research School of Biophysics and Informatics of Autonomous Systems. We received accreditation of the research school from the National Academy of Sciences in 1994 and continued to receive such accreditation ever since. The research school was named after Helmholtz, a lucky choice because many people did not quite understand the description “Biophysics and Informatics of Autonomous Systems”. The participating groups then covered topics from neuro-ethology to robotics. Since then the configuration has changed, groups working on informatics, computer vision and robotics left the school and groups working in the neurosciences, cognition and audiology joined the school. The focus of the school gradually shifted to “Information processing in the human brain related to perception of the environment”. A scientific community thrives by the free exchange of ideas and the critical and inquisitive discussions among their members. I hope that - just as on the previous occassions - this meeting in Bergen will provide the informal and happy playground for such discussions. We are here not just to report on what we have accomplished but perhaps even more so to inspire new ideas. I would like to invite all of you to probe your colleagues’ opinions about the future steps you would like to make. You may find that such discussion may provide the starting point of unexpected alliances to test new ideas. Of course you are here not only to do scientific business. We have a traditional football match and many good meals to savour. You could enjoy some long walks through the dunes or along the beach. We even have had once a dusk-to-dawn wine party, but I am not sure this has been planned for this meeting again. Anyway, the School is happy to offer this opportunity for scientific inspiration. Aspire and acquire!

Bert van den Berg

Scientific director of the Helmholtz Institute


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Our keynote speakers

Peter Neri PhD. Oxford University, Oxford, UK. Lecturer of Experimental Psychology, University of Aberdeen. Dr. Peter Neri obtained his undergraduate degree from the Scuola Normale Superiore in Pisa, where he was taught visual psychophysics by Concetta Morrone and David Burr. A McDonnell-Pew Foundation grant made it possible to move to

Oxford where he completed a DPhil supervised by Colin Blakemore and Andrew Parker. The Wellcome Trust then awarded him an International Prize Travelling Research fellowship to spend 2 years in the US doing fMRI with David Heeger (at Stanford) and 1 year in the UK doing fly single-unit extracellular recordings with Simon Laughlin (Cambridge). At the end of this fellowship, he returned to the US to spend 2 years at UC Berkeley working with Dennis Levi on various topics in visual psychophysics. Last year the Royal Society awarded him a University Research Fellowship extendable to 10 years of funding, during which he intends to push forward the three research directions that he explored in previous years (psychophysics, fMRI and single-unit recordings in insect neurons).

Steven Dakin PhD. 1995 University of Stirling, Scotland Senior Lecturer, University College London Dr. Dakin conducted his PhD at the University of Stirling with Roger Watt before moving to McGill University in Montreal to work with Robert Hess. In 1999 he came back to London to

take up a Career Development fellowship from the Wellcome Trust in order to work with Michael morgan at the Institute of Ophthalmology, University College, and where he was later appointed senior lecturer. His work is primarily concerned with visual integration (how the brain pieces together the mosaic of neural activity images elicit in early visual areas), gain control, and visual processing in several neurological disorders such as schizophrenia and autism.


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List of Participants Participants Helmholtz Retreat 2007 # Name department

1 Aarnoutse, Erik van Universiteit Utrecht, Functional Neurobiology 2 Martijn Agterberg Utrecht Medical Center KNO 3 Alphen, Bart van Erasmus University Rotterdam, Neuroscience 4 Anema, Helen Universiteit Utrecht, Experimental Psychology 5 Baas, Joke Universiteit Utrecht, Experimental Psychology 6 Badura, Alexandra Erasmus University Rotterdam, Neuroscience 7 Battu , Balaraju Universiteit Utrecht, Physics of Man 8 Beers, Rob van Universiteit Utrecht, Physics of Man 9 Benjamins, Jeroen Universiteit Utrecht, Experimental Psychology 10 Bergmann Tiest, Wouter Universiteit Utrecht, Physics of Man 11 Bolhuis, Johan Universiteit Utrecht, Behavioural Biology 12 Borra, Tobias Universiteit Utrecht, Experimental Psychology 13 Boxtel, Jeroen van Universiteit Utrecht, Physics of Man 14 Brascamp.Jan Universiteit Utrecht, Functional Neurobiology 15 Eli Brenner Free University Amsterdam, Human Movement Sciences 16 Brouwer, Gijs Universiteit Utrecht, Physics of Man 17 Bruce, Matt Universiteit Utrecht, Behavioural Biology 18 Bullens, Jessie Universiteit Utrecht, Experimental Psychology 19 Carlson, Tom Universiteit Utrecht, Experimental Psychology 20 Dakin, Steven University College London 21 Dijkerman, Chris Universiteit Utrecht, Experimental Psychology 22 Donker, Stella Universiteit Utrecht, Experimental Psychology 23 Duijnhouwer, Jacob Universiteit Utrecht, Functional Neurobiology 24 Ee, Raymond van Universiteit Utrecht, Physics of Man 25 Erkelens, Casper Universiteit Utrecht, Physics of Man 26 Festen, Joost Free University Amsterdam, Audiology 27 Fonteijn, Hubert Universiteit Utrecht, Experimental Psychology. 28 Frens, Maarten Erasmus University Rotterdam, Neuroscience 29 Gebuis, Titia Universiteit Utrecht, Experimental Psychology 30 Geest, Jos van der Erasmus University Rotterdam, Neuroscience 31 Gobes, Sharon Universiteit Utrecht, Behavioural Biology 32 Goede, Maartje de Universiteit Utrecht, Experimental Psychology 33 Grave, Denise de Free University Amsterdam, Human Movement Sciences 34 Grol, Meike Universiteit Utrecht, Experimental Psychology 35 Haan, Edward de Universiteit Utrecht, Experimental Psychology 36 Ham, Ineke van der Universiteit Utrecht, Experimental Psychology 37 Hogendoorn, Hinze Universiteit Utrecht, Experimental Psychology 38 Honk, Jack van Universiteit Utrecht, Experimental Psychology 39 Hooge, Ignace Universiteit Utrecht, Experimental Psychology


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40 Horst, Bernard van der Universiteit Utrecht, Physics of Man 41 Jong, Maartje de Universiteit Utrecht, Physics of Man 42 Karlsson, Stefan Universiteit Utrecht, Physics of Man 43 Kammers, Marjolein Universiteit Utrecht, Experimental Psychology 44 Kappers, Astrid Universiteit Utrecht, Physics of Man 45 Kenemans, Leon Universiteit Utrecht, Experimental Psychology 46 Klink, Chris Universiteit Utrecht, Functional Neurobiology 47 Klumpers, Floris Universiteit Utrecht, Experimental Psychology 48 Knapen, Thomas Universiteit Utrecht, Functional Neurobiology 49 Koelewijn, Loes Universiteit Utrecht, Experimental Psychology 50 Koenderink, Jan Universiteit Utrecht, Physics of Man 51 Kooij, Katinka van der Universiteit Utrecht, Experimental Psychology 52 Kroeze, Jan Universiteit Utrecht, Experimental Psychology 53 Lankheet, Martin Universiteit Utrecht, Functional Neurobiology 54 Leensen, Monique Academic Medical Center, University of Amsterdam, Audiology 55 Liesker, Hanneke Free University Amsterdam, Human Movement Sciences 56 Lorteije, Jeannette Erasmus University Rotterdam, Neuroscience 57 Maij, Femke Free University Amsterdam, Human Movement Sciences 58 Massen, Jorg Universiteit Utrecht, Behavioural Biology 59 Mello, Claudio Universiteit Utrecht, Behavioural Biology 60 Mierlo, Christa van Free University Amsterdam, Human Movement Sciences 61 Mol, Nisan Universiteit Utrecht, Experimental Psychology 62 Muller, Chris Free University Amsterdam, Human Movement Sciences 63 Mury, Alexander Universiteit Utrecht, Physics of Man 64 Peter Neri University of Aberdeen 65 Nijboer, Tanja Universiteit Utrecht, Experimental Psychology 66 Noest, Andre Universiteit Utrecht, Behavioural Biology 67 Oleksiak, Anna Universiteit Utrecht, Functional Neurobiology 68 Over, Eelco Erasmus University Rotterdam, Neuroscience 69 Overvliet, Krista Free University Amsterdam, Human Movement Sciences 70 Paffen, Chris Universiteit Utrecht, Experimental Psychology 71 Pas, Susan te Universiteit Utrecht, Experimental Psychology 72 Plaisier, Myrthe Universiteit Utrecht, Physics of Man 73 Pont, Sylvia Universiteit Utrecht, Physics of Man 74 Raemaekers, Mathijs Universiteit Utrecht, Functional Neurobiology 75 Reader, Simon Universiteit Utrecht, Behavioural Biology 76 Richter, Janneke Erasmus University Rotterdam, Neuroscience 77 Rijn, Sophie van Universiteit Utrecht, Experimental Psychology 78 Sanders, Bram Universiteit Utrecht, Physics of Man 79 Schonewille, Martijn Erasmus University Rotterdam, Neuroscience 80 Slijper, Harm Erasmus University Rotterdam, Neuroscience 81 Smagt, Maarten van der Universiteit Utrecht, Experimental Psychology 82 Smeets, Jeroen Free University Amsterdam, Human Movement Sciences 83 Sterck, Liesbeth Universiteit Utrecht, Behavioural Biology 84 Stronks, Chris Universiteit Utrecht, UMC Utrecht 85 Struiksma, Marijn Universiteit Utrecht, Experimental Psychology 86 Veenemans, Arielle Universiteit Utrecht, Experimental Psychology 87 Verhagen, Lennart Universiteit Utrecht, Experimental Psychology


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88 Vermaak, Michiel Erasmus University Rotterdam, Neuroscience 89 Verstraten, Frans Universiteit Utrecht, Experimental Psychology 91 Volcic, Robert Universiteit Utrecht, Physics of Man 92 Vries, Han de Universiteit Utrecht, Behavioural Biology 93 Vries, Jelmer de Universiteit Utrecht, Experimental Psychology 94 Warnaar, Bastiaan Academic Medical Center, University of Amsterdam, Audiology 95 Wertheim, Lex Universiteit Utrecht, Experimental Psychology 96 Wezel, Richard van Universiteit Utrecht, Functional Neurobiology biology 97 Wijntjes, Maarten Universiteit Utrecht, Physics of Man 98 Wismeijer, Dagmar Universiteit Utrecht, Physics of Man 99 Zandvoort, Martine van Universiteit Utrecht, Experimental Psychology


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Program & Abstracts Wednesday 13 JUNE 9.30 – 10.30 Arrival, coffee/tea & cake 10.45 Opening – Frans Verstraten. Session 1 – Perception of illumination and materials in natural scenes (Moderator: Sylvia Pont) 10.55 – 11.00 Sylvia Pont - Introduction 11.00 – 11.20 Stefan Karlsson – Illuminance flow 11.20 – 11.40 Tanja Nijboer – Brightness Agnosia: a Disorder of Bright- and Darkness

Recognition 11.40 – 12.00 Alex Mury – Properties of light fields in natural scenes 12.00 – 12.20 Susan te Pas – Illumination discrimination performance for object images 12.30 – 14.00 Lunch & sniff-some-good-air-time Session 2 – Combination of depth cues for perception and motor control (Moderator: Jeroen Smeets) 14.00 – 14.20 Dagmar Wismeijer – Perspective information influences vergence with binocular

disparity present, but perceived surface slant does not. 14.20 – 14.40 Christa van Mierlo – Timing differences between visual cues for the online control

of movement. 14.40 – 15.00 Gijs Joost Brouwer – Perceptual incongruence between depth cues influences

bistability and cortical activation. 15.00 – 15.20 Refreshments/coffee/Tea 15.20 – 15.40 Chris Muller – Maybe they are all circles. 15.40 – 16.00 Katinka van der Kooij – Curvature contrast trancends stereopsis and Structure-

From-Motion modalities. Walk on the beach/drinks/whatever you feel like 18.00 – 19.45 Diner Keynote lecture 1 (Moderator: Richard van Wezel) 20.15 – 21.00 Visual perception of biological movements Dr. Peter Neri (University of Aberdeen) 21.15 Bar & Poster Session (organized by Helmholtz PhD Student Council)


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Thursday 14 JUNE 06.00 – 07.00 Early bird walk/run/swim 07.00 – 08.45 Breakfast Session 3 – Social Cognition (Moderator: Simon Reader) 09.00 – 09.20 Sharon Gobes – The neural substrate of song memory in zebra finches. 09.20 – 09.40 Simon Reader – Social and individual information use in humans exploring a

changing artificial environment. 09.40 – 10.00 Liesbeth Sterck. – Post-conflict behaviour in chimpanzees. 10.00 – 10.30 Coffee/tea Session 4 – Haptic Perception 1 (Moderator: Chris Dijkerman ) 11.30 – 10.50 Myrthe Plaisier – Subitizing in active touch. 10.50 – 11.10 Krista Overvliet – Are fingers represented somatotopically or spatially? 11.10 – 11.30 Helen Anema – Investigations of impairment in finger representation in a patient

with GerstmannÕs syndrome. 11.30 – 11.50 Maarten Wijntjes – Curvature contrast in haptic perception. 11.50 – 12.10 Bram Sanders – Curvature affects haptic length perception. 12.15 – 14.00 Lunch & sniff-some-fresh-air-time Session 5 – Haptic Perception 2 (Moderator: Astrid Kappers) 14.00 – 14.20 Wouter Bergmann Tiest – The psychophysics of elasticity. 14.20 – 14.40 Marjolein Kammers – Erasing the Rubber Hand Illusion: Task dependent

recalibration of an illuded limb. 14.40 – 15.00 Hanneke Liesker – Visual and haptic search: Do eyes and hands perform tasks in

parallel and independently. 15.00 – 15.20 Refreshments/coffee & tea. 15.20 – 15.40 Robert Volcic – Haptic mental rotation: a window into the coding of object

orientation. 15.40 – 16.00 Bernard van der Horst – Transfer of the haptic aftereffect. 16.00 – 17.00 EVENT: Prepare a proposal, organized by Maarten & Wouter 17.00 – 18.00 walk on the beach/drinks/whatever you want to do 18.00 – 19.45 Diner BBQ Keynote lecture 2 (Moderator: Frans Verstraten) 20.00 – 21.00 Face perception: From bar codes to face space Dr. Steven Dakin (University College London) 21. 00 EVENT: Award ceremony prepare a proposal


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Friday 15 JUNE 06.00 – 07.00 Beach exercise/walk/swim 07.00 – 08.45 Breakfast Session 7 - Perception of bi-stable visual stimuli (Moderator: Richard van Wezel) 09.00 – 09.20 Chris Klink – How Interactions between stimulus timing, perceptual history and

voluntary control determine perceptual decisions. 09.20 – 09.40 Thomas Knapen – Stimulus motion propels traveling waves in binocular rivalry. 09.40 – 10.00 Jan Brascamp – History dependence in perception of ambiguous stimuli. 10.00 – 10.20 Jeroen van Boxtel – Temporal form parsing dictates binocular conflict resolution in

dynamic visual stimuli. 10.30 – 11.00 Coffee/Tea Session 8 – Of mice and men: Neuroscience in Rotterdam (Moderator: Jos van der Geest) 11.00 – 11.20 Janneke Richter - The accuracy of estimating computer work duration 11.20 – 11.40 Alexandra Badura - The role of the GABA-ergic input to Purkinje cells in

compensatory eye movements 11.40 – 12.00 Jeannette Lorteije – Inhibition and auditory processing in areas MNTB and MSO 12.00 – 12.20 Bart van Alphen – Mouse eye movements in response to optokinetic noise stimuli 12.30 – 14.00 Lunch & sniff-some-fresh-air-time 14.00 – Whatever you feel like!


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Program 4th Helmholtz Retreat 2007 Wednesday 13 JUNE Session 1 – Perception of illumination and materials in natural scenes (Moderator: Sylvia Pont) 10.55 – 11.00 Sylvia Pont - Introduction 11.00 – 11.20 Stefan Karlsson – Illuminance flow 11.20 – 11.40 Tanja Nijboer – Brightness Agnosia: a Disorder of Bright- and Darkness Recognition 11.40 – 12.00 Alex Mury – Properties of light fields in natural scenes 12.00 – 12.20 Susan te Pas – Illumination discrimination performance for object images 10.55 – 11.00 Sylvia Pont – Introduction “Ecological optics” (Gibson, 1950) is complicated to

describe due to aspects such as non-convex shapes, colour, surface roughness at a variety of scales, shadows and interreflections. An integral solution must also take into account optical interactions in scenes such as between the influence of objects on light fields and the influence of the light field on the appearance of objects. Nonetheless, without any effort, and even without being aware of it, our brain (usually) reckons with such optical mechanisms in the perception of our daily environment. Moreover, we can even derive fairly complete representations of scenes from single greyscale images! Why then is it so hard to design robots that derive the same properties from images?

11.00 – 11.20 Stefan Karlsson – Illuminance flow Traditionally in computer vision/graphics, one

modelled texture as the presence of non-glossy paint on a surface. However, texture can also be constructed when the paint is uniform (a wall made of cement, for instance). In reality, most textures are made up of a combination of these two extremes (fine-scale corrugations (3D-texture) vs. flat albedo-patterns (matte paint)). One of the factors that determine the appearance of texture is the structure of the light field. The appearance of 'matte paint texture' will change uniformly with varying light fields. The appearance of '3D texture', on the other hand, is predominantly determined by the structure of the light-field, because the contrast arising is a combination of shading, shadowing and vignetting. Humans do not have the problems that computer vision has with 3D-texture. We will present the theory we have developed into the so-called illuminance flow, which can be used for global shape inductions based on the appearance of 3D texture. This differs from traditional "shape from texture", where only the albedo-pattern (the 'paint') is used. This talk will focus on the estimation and prediction of illuminance flow for smooth objects with 3D-texture.

11.20 – 11.40 Tanja Nijboer – Brightness Agnosia: a Disorder of Bright- and Darkness

Recognition We report a patient with extensive brain damage involving the right hemisphere, who demonstrated a severe impairment in the appreciation of brightness. Acuity, contrast sensitivity as well as luminance discrimination were normal, suggesting her brightness impairment is not a mere consequence of low-level sensory impairments. The patient was not able to indicate the darker or the lighter of two grey squares, even though she was able to see that they differed. In addition, she could not indicate whether the lights in a room were switched on or off, nor was she able to differentiate between normal greyscale images and inverted greyscale images. As the patient recognised objects, colours, and shapes correctly, the impairment is specific for brightness. This is the first report of a selective deficit in brightness recognition or ‘brightness agnosia’.

11.40 – 12.00 Alex Mury – Properties of light fields in natural scenes Light fields of natural

scenes are highly complex and vary within a scene from point to point. However, in many applications complex lighting can be successfully replaced by its low order approximation. The purpose of this research was to investigate the spatial behaviour


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of light fields in natural scenes. We describe the light fields in terms of spherical harmonics and analyze their qualitative properties and the effect of different components of the light field on objects appearance. We show that low order approximations of natural light fields vary smoothly and systematically within scenes, in accordance with very simple models, and that low order components dominate the light field in natural scenes. We also show the effects of different components of the light field light field on objects appearances. Taking into account that it is the second order representation that is mainly responsible for the appearance of diffuse objects, the typical patterns of low order distributions can be used in applications. Furthermore, these findings suggest that natural light fields can be described using a combination of a simple physical model for the second order part, plus a statistical description of the higher order terms.

12.00 – 12.20 Susan te Pas – Illumination discrimination performance for object images The

appearance of objects in natural scenes is determined by their reflectance, their surface roughness, their shape and by the nature of the illumination. Results of previous experiments suggested that perception of material and illumination are basically confounded, and that illumination perception depends mainly on simple cues such as the location of the shadow edge. In the present study we investigate whether this conclusion can be extended to images of real objects under varying complexity of illumination, 3D texture and shape. We find that even in images of real objects perception of material and illumination are basically confounded. Overall, illumination and material are confounded most when we present rendered spheres that differ only in reflectance mode under simple canonical illumination conditions. Interestingly, adding complex natural illumination containing higher order angular frequencies does not help to disambiguate this confound in illumination judgments. Most helpful was the addition of 3D texture. We found that low spatial frequency manifestations of the illumination, such as average direction of the illumination and maybe an ambient term, can be discriminated, but high spatial frequency features, such as number of sources are almost impossible to distinguish. Introducing complex shapes to the scene made the identification of such features of the light field even more difficult.

Session 2 – Combination of depth cues for perception and motor control (Moderator: Jeroen Smeets) 14.00 – 14.20 Dagmar Wismeijer – Perspective information influences vergence with

binocular disparity present, but perceived surface slant does not. 14.20 – 14.40 Christa van Mierlo – Timing differences between visual cues for the online

control of movement. 14.40 – 15.00 Gijs Joost Brouwer – Perceptual incongruence between depth cues influences

bistability and cortical activation. 15.20 – 15.40 Chris Muller – Maybe they are all ellipses; uncertainty about the assumptions

influences cues' weights. 15.40 – 16.00 Katinka van der Kooij – Curvature contrast trancends stereopsis and

Structure-From-Motion modalities. 14.00 – 14.20 Dagmar Wismeijer - Perspective information influences vergence with

binocular disparity present, but perceived surface orientation does not. We studied the influence of perceived surface orientation on vergence accompanying a saccade while viewing an ambiguous stimulus. We used the slant rivalry stimulus, in which perspective foreshortening and disparity specified opposite surface orientations. This rivalrous configuration induces alternations of perceived surface orientation, while the slant cues remain constant. Subjects were able to voluntarily control their perceptual state while viewing the ambiguous stimulus. They were asked to make a saccade across the perceived slanted surface. Our data show that vergence responses closely approximated the vergence response predicted by the disparity cue, irrespective of voluntarily controlled perceived orientation. However,


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comparing the data obtained while viewing the ambiguous stimulus with data from an unambiguous stimulus condition (when disparity and perspective specified similar surface orientations) revealed an effect of perspective cues on vergence. Collectively our results show that depth cues rather than perceived depth govern vergence.

14.20 – 14.40 Christa M. van Mierlo - Timing differences between visual cues and online

control of movement. Across-attribute and within-attribute visual cues have been found to be processed independently with varying neural latencies in different areas of the brain. Consequently, synchronous events that occur in cues in our external world might get asynchronized in our brain. How does the brain deal with this when an event occurs in more than one cue? In a purely perceptual task, subjects benefited from combining such cues even when there was a 100 ms timing difference between them (Van Mierlo, Brenner, Smeets, 2007). Latency differences between cues might be more of an issue for perceptual-motor tasks, in which the timing of information is vital for the online control of action. We studied timing differences between cues in a virtual environment where we could independently manipulate slant indicated by binocular disparity and texture gradient. A real-world cylinder had to be placed on a target location of a virtual surface that coincided with a real surface. When subjects started to move, the simulated surface could change slant in the two cues simultaneously or with a 100 ms timing difference. To ascertain a correct landing, subjects had to readjust the orientation of their hand and arm before placing the object on the surface. When the changed occurred simultaneously in the two cues, or 100 ms later in stereo than in texture, correctionsin angle and velocity appeared 75 ms after the first change. When the change was presented 100 ms later in texture, corrections appeared 140 ms after the first change. So texture gradient appears to be processed approximately 70 ms faster than binocular disparity, and corrective movements seem to be based on the cue that provides information about the change in surface slant first.

14.40 – 15.00 Gijs Joost Brouwer - Perceptual incongruence between depth cues influences

bistability and cortical activation. Human depth perception depends on a multitude of cues which, when combined, allow the visual system to represent the spatialorganization of our environment. To study mechanisms underlying our conscious perception of depth, we used the paradigm of bistability. During prolonged viewing of bistable stimuli, observers’ perceptual states will alternate from one to the other possible interpretation provided by the stimulus. Bistability presents us with an ideal tool for studying perceptual processes: it allows us to dissociate constant sensory input from changes in perception. In slant rivalry (van Ee, 2002), bistability results from incongruence between two slant-defining cues: binocular disparity and monocular perspective. As a result, the stimulus is perceived as alternating between a perspective-dominated percept (monocular depth) and a disparity-dominated percept (stereopsis). We used slant rivalry and functional imaging to investigate the neural correlate of depth perception, as well as the effect of conflict or incongruence between perceptual interpretations on the dynamics of bistable perception and cortical activation. In a first series of experiments, we showed that mainly dorsal visual areas (V3A, V7 and V4d-topo) show transient activation at the time of a perceptual alternation towards the disparity-dominated percept. In others words, these areas appear to signal the instigation of stereopsis. Converging evidence was obtained using stereo-images of natural scenes. Both areas V7 and V4d-topo show an increase in activation when the stereoscopic depth information is perceived, relative to a situation in which this same stereoscopic information is present, but suppressed because it is incongruent with pictorial information.In a second series of experiments, we attempted to characterize the processes underlying bistability, and the way its dynamics depend on stimulus characteristics. Our goal was to determine the influence of the degree of incongruence between perceptual states on the temporal dynamics of bistability and its effect on cortical activation. If the level of incongruence between perceptual interpretations has a clear influence on the dynamics of bistable perception, it demonstrates that the brain takes into account the differences between interpretations in its attempt to reconcile these into a coherent and stable perceptual experience. Indeed, we found that the more both perceptual


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states differ from each other, the more vigorous and rapidly subjects alternate between these states. These increases in alternation rate were paralleled by increases in activation within the anterior part of the parietal cortex. We suggest that this cortical activity predicts the frequency of subsequent alternations, implying a putative causal role for these areas in detecting the level of incongruence between depth cues and initiating bistable perception.

15.20 – 15.40 Chris Muller - Maybe they are all ellipses; uncertainty about the assumptions

influences cues' weights Humans judge surface slant from a weighted average of cues, with more reliable cues receiving more eight. Cues that provide more precise estimates are obviously more reliable, but many cues also rely on assumptions about the statistics of the world. For instance, many monocular slant cues rely on the ssumption that the surface in question is isotropic. Is the possibility that this assumption is incorrect onsidered when assigning weights to the cues? Are only the statistics of scenes in general considered, or also specific information from the scene in question? We asked subjects to match the slant of an elliptical target (with monocular and binocular cues indicating slightly different slants) by setting the slant of a large surrounding surface. To strengthen the assumption that the (textured) target was isotropic (circular) it was rotating without its outline changing and the surrounding surface consisted of rotating circles. For comparison we presented static targets surrounded by rotating ellipses with various aspect ratios. In the former case subjects relied less heavily on binocular information.

15.40 – 16.00 Katinka van der Kooij - Curvature Contrast Transcends Cue Modalities. The

general lay out of a scene influences shape perception, as is shown in shape contrast effects where the perception of one shape is distorted in the direction opposite to another shape. So-called cue combination models describing the perception of 3-D shape are based on the assumption that the overall shape estimate is a weighted linear combination of the estimates derived from the individual cues. These models explain shape contrast on the cue level, before cue integration. However, curvature contrast effects for motion-, shading-and-texture and stereoscopically defined stimuli are all of the same order and magnitude. This suggests that these contrast effects are independent of cue system. We investigated the question whether the curvature contrast effect transcends stereopsis and structure-from-motion cue modalities. To do this, we presented the test shape and inducers either in the same cue (stereopsis) or in different cues (stereopsis and structure-from-motion) and compared the curvature contrast effect we found in the two conditions. We found a consistent contrast effect in the same-cue as well as in the combined cue condition, showing that the curvature contrast effect transcends stereopsis and structure-from-motion cue modalities.

Keynote lecture 1 (Moderator: Frans Verstraten) 20.15 – 21.00 Dr. Peter Neri - Visual perception of biological movements. I will discuss a

multi-stage processing scheme for the perceptual analysis of biological motion, and present results from psychophysical experiments that target some of the stages in the processing hierarchy leading from local motion detection to the representation of multiple agents. I will focus primarily on recent results demonstrating that meaningful interactions between perceived human agents can enhance their visual discriminability, but will also discuss some results on the recognition-by-parts nature of agent identification.

21.15 Bar & Poster Session (organized by Helmholtz PhD Student Council)


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Thursday 14 JUNE Session 3 – Social Cognition (Moderator: Simon Reader) 09.00 – 09.20 Sharon Gobes – The neural substrate of song memory in zebra finches. 09.20 – 09.40 Simon Reader – Social and individual information use in humans exploring a

changing artificial environment. 09.40 – 10.00 Liesbeth Sterck. – Post-conflict behaviour in chimpanzees. 09.00 – 09.20 Sharon Gobes - The neural substrate of song memory in zebra finches Juvenile

songbirds, such as zebra finches (Taeniopygia guttata), learn their song from an adult tutor male in a process which is similar to human speech acquisition. Recent evidence suggests that the neuronal representation of song memory is localized to the songbird equivalent of the auditory association cortex, the caudomedial nidopallium (NCM). To investigate whether the NCM is (part of) the neural substrate for the representation of tutor song, the bird’s own song, or both, we examined the effects of bilateral neurotoxic lesions to the NCM on song production, song recognition and discrimination. Here we demonstrate that the NCM is (part of) the neural substrate for tutor song memory, since lesions to the NCM did not affect the males’ song production, but did impair tutor song recognition. Our results demonstrate that at least two distinct memory systems are functioning in parallel in the songbird brain, one involved in producing birds’ own song, and one that contains the neural representation for tutor song. Thus, in both humans and songbirds, the cognitive systems of vocal production and auditory recognition memory are subserved by distinct brain regions.

09.20 – 09.40 Simon Reader and Ulf Toelch (Utrecht University): Social and individual

information use in humans exploring a changing artificial environment Individuals can make use of information gathered personally (individual information) or from others (social information) to track environmental change. Mathematical models make clear predictions regarding the rates of environmental change at which a reliance on a social versus individual information gathering strategy would be adaptive, but these models, and the issue of individual flexibility in the strategy employed, have not been subject to rigorous empirical test. Participants (62 adult males and females) explored a virtual three-dimensional computer maze, with a forced choice between four reward locations. There were three low-value and one high-value reward, and monetary earnings were proportional to the total reward located. The three experimental treatments were high, low, and intermediate environmental variability, represented by the probability that the high-reward location moved between rounds. On the first 20 rounds, participants explored the maze alone. On the subsequent 80 rounds, participants were also allowed to view a virtual player exploring the maze. Participants tended to use the social information available from the virtual player more as environmental variability decreased. These results are in line with the predictions of evolutionary models. Moreover, they suggest that humans flexibly adjust their information gathering strategy according to the prevailing environmental variability.

09.40 – 10.00 Sonja Koski and Elisabeth Sterck (Utrecht University): Post-conflict behaviour

in chimpanzees Affiliation after a conflict is common to many gregarious species with individualized societies. Affiliation between the former opponents, also called reconciliation, is suggested to repair the damaged relationship between the opponents and to decrease post-conflict anxiety. Also affiliation between an opponent and an uninvolved individual, called third-party-initiated affiliation or consolation, is assumed to calm the opponent. We tested the function of these two types of post-conflict affiliation in captive chimpanzees (Pan troglodytes) in the Arnhem Zoo, the Netherlands. Our study supported the hypothesis that reconciliation repairs the relationship of the opponents. However, post-conflict anxiety only appeared in aggressees but not in aggressors of conflicts. This suggests that post-conflict anxiety depends on the role of the participant in the conflict. Third-party initiated affiliation,


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however, failed to reduce stress in opponents. We tested an alternative hypothesis, addressing whether it benefits the affiliators by protecting them from further aggression by conflict opponents. The self-protection function applied to most third-party-initiated affiliation events. However, a subset of affiliation, provided to victims by their own kin, may reflect reasons other than self-protection, since kin received significantly less often redirected aggression and yet they frequently affiliate with victims. Thus, post-conflict affiliation serves multiple functions, depending on the role in the conflict of the involved animals, and the relationship attributes between them.

Session 4 – Haptic Perception 1 (Moderator: Chris Dijkerman ) 11.30 – 10.50 Myrthe Plaisier – Subitizing in active touch. 10.50 – 11.10 Krista Overvliet – Are fingers represented somatotopically or spatially? 11.10 – 11.30 Helen Anema – Investigations of impairment in finger representation in a

patient with GerstmannÕs syndrome. 11.30 – 11.50 Maarten Wijntjes – Curvature contrast in haptic perception. 11.50 – 12.10 Bram Sanders – Curvature affects haptic length perception. 11.30 – 10.50 Myrthe Plaisier - Subitizing in active touch From visual studies it is known that

people can judge the number of dots presented on a display fast, accurately and almost effortlessly up to three of four items through a mechanism labeled subitizing. For larger numbers of items enumeration is more error-prone and response times increase strongly with the number of items. Subitizing has also been shown to exist in other modalities such as audition. Enumeration studies in touch have been restricted to ‘passive touch', i.e. touch without active exploration. In daily life, when we count the number of coins in our pocket we do this through active touch and the items can be actively rearranged. We asked subjects to haptically explore varying numbers of spheres and to enumerate them as fast as possible. Our results show that people can subitize up to three items using active touch. Furthermore, we conclude that efficient performance in the subitizing regime could not be attributed to subjects using only mass and volume cues to estimate numerosity.

10.50 – 11.10 Krista Overvliet - Are fingers represented somatotopically or spatially? To

investigate whether somatosensory information perceived by our fingers, is coded within a somatotopical or a spatial representation we conducted an experiment in which subjects had to locate tactile stimuli applied to their fingertips. The tactile stimulus was a Von Frey hair at threshold level, and could be applied to one of thirty positions (three evenly distributed and aligned positions per fingertip). These thirty positions were numbered and presented on a map of two hands. The task for the subject was to name the number corresponding to the perceived position of the stimulus. If they did not perceive the stimulus, they were asked to guess its position. We measured the number and locations of errors that subjects made in three conditions: fingers together, fingers spread and fingers woven. We reasoned that if the error rate and distribution are the same in all three conditions, somatosensory information, perceived by our fingers, is coded within a somatotopical reference frame. However, if fewer errors are made when the fingers are spread, coding is realized within a spatial reference frame. We found that most errors were made when the fingers were together or woven. Subjects made significantly fewer errors when the fingers were spread. This implies that when localizing near-threshold tactile stimuli applied to the fingers, tactile information is coded spatially.

11.10 – 11.30 Helen Anema - Investigations of impairment in finger representation in a

patient with Gerstmann’s syndrome In 1930 Joseph Gerstmann indicated a disruption in body representation, and in particular the representation of fingers and hands, as the “grundstörung” of the Gerstmann syndrome (acalculia, agraphia, finger agnosia). Ever since left/right disorientation has been added to this cluster of impairments, ideas about a common cognitive denominator shifted towards the


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spatial domain (mental manipulation of images Mayer et al (1999)). Here we present a case study of a right-handed 51 year old stroke patient who suffered from a watershed infarction (left parieto-occipital area) with left/right disorientation, finger agnosia, acalculia and agraphia. In a series of tests we investigated which aspects of finger representation were impaired in this patient. We assessed whether the deficit was related to the response given (motor or perceptual), the influence of visual and somatosensory input and the ability to integrate sensory input across fingers. The results suggest that a spatial impairment cannot account entirely for the finger agnosia in this patient and will be discussed in relation to recent models of body and hand representations.

11.30 – 11.50 Maarten Wijntjes - Curvature contrast in haptic perception. When one explores

a raised line drawing or a 3D object, quite often the fingers are touching different geometrical properties simultaneously. It is likely that these properties interact. We studied how a curved line presented on one finger influences the perceived straightness on the other finger. For both raised line stimuli and 3D objects we measured points of subjective straightness. We also measured the movement of the fingers with respect to the hand to understand how the hand is used as reference frame.

11.50 – 12.10 Bram Sanders - Curvature affects haptic length perception Abstract: One

possible way of haptically perceiving length is to trace a certain path with one’s index finger and estimate the traversed distance. A long-known illusion in this respect is the so-called Radial/Tangential-effect for whole-arm movements in the horizontal plane: linear extents oriented radially from the trunk are overestimated relative to tangentially oriented extents. Several researchers have noted that observers need longer times to execute radial arm movements compared to tangential movements. However, the basis for this illusion remains still unsolved. Here we present a new experiment in which observers judge lengths of paths across cylindrically curved surfaces. Movement profiles of the index finger were recorded with an OptoTrak system. We found that convex and concave surfaces had qualitatively different effects: convex lengths were overestimated, whereas concave lengths were underestimated. In addition, we observed that the index finger moved slower along the convex surface compared to the concave one, which led to longer movement times for convex lengths. Indeed, the high correlation between movement times and length estimates we found shows that observers take the duration of movement as a measure of perceived length. Apparently, observers misperceive lengths of curved pathways because they don’t take speed differences into account. Thus, in a task that is completely different from the Radial/ Tangential-effect similar processes seem to be at work. We further investigated whether these speed differences are caused by gravity modulating movement speeds along the different surface types and discuss why observers failed to account for speed differences.

Session 5 – Haptic Perception 2 (Moderator: Astrid Kappers) 14.00 – 14.20 Wouter Bergmann Tiest – The psychophysics of elasticity. 14.20 – 14.40 Marjolein Kammers – Erasing the Rubber Hand Illusion: Task dependent

recalibration of an illuded limb. 14.40 – 15.00 Hanneke Liesker – Visual and haptic search: Do eyes and hands perform tasks

in parallel and independently. 15.20 – 15.40 Robert Volcic – Haptic mental rotation: a window into the coding of object

orientation. 15.40 – 16.00 Bernard van der Horst – Transfer of the haptic aftereffect.


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14.00 – 14.20 Wouter Bergmann Tiest - The psychophysics of elasticity. Psychophysical laws that hold in all cases are few and far between. But also natural laws have been shown to only hold within explicitly defined boundaries. Similarly, it could be that for psychophysical laws, the specific circumstances are important for the relationship between stimulus and perception. In this talk, results are presented of an experiment designed to investigate the role of stimulus thickness and finger span with respect to the perception of elasticity. A wide range of silicon rubber stimuli were fabricated and characterised. With these, discrimination and matching experiments were performed.

14.20 – 14.40 Marjolein Kammer - Erasing the Rubber Hand Illusion: Task dependent

recalibration of an illuded limb. An accurate representation of body position is not only a necessary parameter for any correct motor command, it also forms an important part of our conscious bodily experience. A classical way to deceive the consciously perceived location of a limb is through the Rubber Hand Illusion (RHI). Whereby synchronous stroking of a visual rubber hand (RH) and the congruent occluded real hand induces a feeling of ownership, which leads to a recalibration of the real hand towards the RH. Currently, the necessary conditions to induce the illusion seem to be visual congruence between the RH and the real hand, in combination with synchronous tactile and visual input during stroking. However, it has not yet been investigated whether the proprioceptive shift towards the rubber hand depends on the given type of response, nor whether new proprioceptive information will erase the illusion. In talk we will present the result of an RHI experiment, which shows a dissociation between illusion insensitive motor responses and illusion sensitive perceptual responses. Furthermore, we challenge the current view that any proprioceptive update through movement of the hand would erase the illusion by showing a significant RHI effect for the perceptual response even after active movement with the illuded limb. These results are in line with the currently most used dissociation between two body representations based on neuropsychological patients. Whereby the body schema is considered to be a bottom-up dynamic representation sub serving action and the body image is thought to be a more stable representation underlying perceptual judgments.

14.40 – 15.00 Hanneke Liesker - Visual and haptic search: Do eyes and hands perform tasks

in parallel and independently? When performing everyday tasks, we often fixate an object before we manipulate it. But eyes and hands do not always move to the same spot; they can also perform tasks in parallel. In order to find out whether the eyes and the hand also perform tasks in parallel and independently in search, we had 10 subjects perform a combined visual and haptic search for one target present in both modalities and compared their search times to those on visual only and haptic only search tasks. In addition to the target, we added a varying number of distractors in the visual display. In the visual conditions with a small number of distractors search times were shorter than in the haptic search condition. In the visual conditions with a large number of distractors search times were longer than in the haptic search condition. Based on these search times, three models were built to predict search times in the combined task. Model 1: combined search is visual search for a small number of distractors and haptic search for a large number of distractors. Model 2: in combined search subjects move their eyes and hand in parallel and independently. Model 3: in combined search subjects’ eyes and hand each search a different part of the display and meet somewhere in between. Search times in the combined search task best matched the prediction by the parallel model.

15.20 – 15.40 Robert Volcic - Haptic mental rotation: a window into the coding of object

orientation. The nature of the reference frame involved in the haptic coding of object orientation was addressed by means of the mental rotation paradigm (Shepard and Metzler, Science: 1971). In the classical paradigm, reaction times increased as a linear function of the angular difference between stimuli, suggesting that participants mentally rotate one object into congruence with the other to judge if the two stimuli are the same or different. In vision the fastest reaction time corresponded to a zero angular difference between the two objects. In the present study, two hand-sized


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objects were simultaneously explored by the two hands. The objects could differ in orientation, and the participant’s task was to decide whether the two objects were structurally the same or mirror-objects. This task was performed in three conditions in which both hand orientations and the locations of the objects with respect to the body were manipulated. The mental rotation paradigm is well suited to study the involvement of reference frames in haptics. Hypothetically, the orientation of an object could be coded in different reference frames (external, hand-centered, body-centered) or even in a combination of these frames. The fastest reaction time would then occur in what is defined to be the angular alignment in a particular reference frame. Since the different reference frames predict different outcomes for the three experimental conditions, the reference frame that is used in the coding of the orientation would be determined by observing the phase shifts of the reaction time function. The experimental data show that the phase shifts closely follow the changes in hand orientations. We suggest that the orientations of the objects are predominantly coded with respect to the hand-centered reference frame, with a minor influence of the body-centered and the external reference frame.

15.40 – 16.00 Bernard van der Horst - Transfer of the haptic aftereffect. The haptic aftereffect

of curvature is the phenomenon that a flat surface is judged concave if the preceding touched stimulus was convex and is judged convex if the preceding touched stimulus was concave. We used this robust phenomenon to investigate how a stimulus presented to one finger influences the perception by another finger. To measure the size of the aftereffect, a subject first touched a conditioning surface for a period of 10 seconds and subsequently touched a test surface, with the same or a different finger. The task was to indicate whether the test surface felt convex or concave. The point of phenomenal flatness was obtained by fitting psychometric functions to the data. When spherically curved conditioning surfaces were statically touched by the tip of an index finger, a small transfer of the aftereffect to other fingers of the same hand was found. Preliminary results of an experiment in which subjects move their finger over the stimulus surface indicate that the aftereffect might even transfer to the opposite hand.

Keynote lecture 2 (Moderator: Frans Verstraten) 20.00 – 21.00 Dr. Steven Dakin - Face perception: From bar codes to face space. Our ability

to extract a wide range of information from faces under a huge range of viewing conditions is one of the most impressive features of human visual processing. This talk presents two streams of evidence bearing on the issue of (a) how we extract feature and configuration information from faces and (b) how we represent facial identity within the multi-dimensional encoding scheme known as "face space". Considering the face as a signal, then it is reasonable to assume that its efficiency at conveying information arises from it being well matched to the operating characteristics of the intended receiver: the human visual system. I show that there is indeed a simple relationship between the structure of faces and the structure of the early visual system. Faces elicit a highly characteristics pattern of clustered response in the output of simulated V1 horizontally oriented receptive fields, a pattern I refer to as the "barcode". These patterns are essentially one-dimensional and I discuss both how this could confer computational advantages for face processing and how this can account for our well-documented vulnerability to certain non-ecological facial transformations (such as spatial and polarity inversion). The second half of the talk describes recent work looking at how the visual brain could use the raw feature information derived from simple filtering mechanisms to encode facial identity. It is widely held that the neural representation of faces may be viewed as a multi-dimensional "face-space" with the average at its origin. Under this view the distance between faces encodes their similarity, and distance from the origin encodes general "distinctiveness". Here we investigate the so called "identity axis" of face space, (the line extending from the origin or average face to any given face) comparing objective and subjective measures of distinctiveness to


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uncover the nature of the dimensions supporting it. By modifying established "pedestal" (TvC) paradigms from the contrast discrimination literature I show that one can psychophysically infer underlying "identity response function" for faces. I show that these functions exhibit modest non-linearities and can be brought into registration across observers and faces, using a single scalar based on the observers' best discrimination performance. This threshold is closely related to the subjective distinctiveness of the face. From this one can conclude that the distinctiveness of a face is predicted not just by its discriminability from the average, but also its best discriminability from a modified version of itself. I discuss implications of these findings for identity encoding schemes that are centred either on the average face versus those centred on multiple exemplar faces.

21. 00 EVENT: Award ceremony prepare a proposal


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Friday 15 JUNE Session 7 - Perception of bi-stable visual stimuli (Moderator: Richard van Wezel) 09.00 – 09.20 Chris Klink – How Interactions between stimulus timing, perceptual history and

voluntary control determine perceptual decisions. 09.20 – 09.40 Thomas Knapen – Stimulus motion propels traveling waves in binocular rivalry. 09.40 – 10.00 Jan Brascamp – History dependence in perception of ambiguous stimuli. 10.00 – 10.20 Jeroen van Boxtel – Temporal form parsing dictates binocular conflict

resolution in dynamic visual stimuli. 09.00 – 09.20 Chris Klink – How Interactions between stimulus timing, perceptual history and

voluntary control determine perceptual decisions. When the brain is confronted with a bi-stable visual stimulus it chooses to consciously perceive one of the two perceptual interpretations. We studied this percept-choice process by intermittently presenting ambiguous structure from motion spheres and binocular rivalry gratings while varying the timing of both presentation duration and interstimulus interval (ISI). Percept-choices were dependent on the perceptual history and the length of the ISI but independent of the presentation duration. Short ISI’s favored choice-alternation while long ISI’s favored choice-repetition. Furthermore, subjects were able to voluntarily control the alternation probability of the stimuli but the removal-time dependency of the perceptual decision was still present. These findings suggest that the temporal dynamics of percept-choices in bi-stable vision are determined by low-level interactions, but that the decision process can be modulated by top-down mechanisms of voluntary control. With model-simulations we show that the choice process can be explained in terms of cross-inhibition, adaptation and a near-threshold neural baseline. These simulations also show that the top-down modulation of voluntary control can be understood as attentional gain modulation in early stage of visual processing that precede the stage where the rivalry is resolved and the perceptual decision is made.

09.20 – 09.40 Thomas Knapen – Stimulus motion propels traveling waves in binocular rivalry.

In visual perception, transitions between the two mutually exclusive percepts that alternate when the two eyes view conflicting stimuli (binocular rivalry) may take shape as traveling waves. The properties of these waves point to a neural substrate of binocular rivalry alternations that has the hallmark signs of lower cortical areas. In a series of experiments, we show a potent interaction between traveling waves in binocular rivalry and stimulus motion. The course of the traveling wave is biased in the motion direction of the suppressed stimulus that gains dominance by means of the wave-like transition. Thus, stimulus motion may propel the traveling wave across the stimulus to the extent that the stimulus motion dictates the traveling wave's direction completely. Using a computational model, we show that a speed-dependent asymmetry in lateral inhibitory connections between retinotopically organized neurons can explain our results. We argue that such a change in suppressive connections may play a vital role in the resolution of dynamic occlusion situations.

09.40 – 10.00 Jan Brascamp – History dependence in perception of ambiguous stimuli. We

have shown that perception of a reappearing ambiguous figure is biased by a multi-timescale history of prior perception. Brief dominance of a percept on past presentations leaves a bias toward that same percept for seconds to come, whereas prolonged dominance leaves a minute-scale bias. In case competing percepts dominate alternately at different timescales (e.g. one persistently and the other incidentally interrupting), opposite biases evolve in parallel. Here we study how the influence of prior perception builds up and decays over time. We present an ambiguous stimulus intermittently until one percept dominates on a preset number of consecutive presentations. Then, following a pause of preset duration, we resume intermittent presentation and ask if the percept equals the one before the pause. During the pause subjects receive visual stimulation or view a blank screen. We find that the influence of past perception decays slowest without visual stimulation.


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Moreover, decay is faster for a percept that dominated briefly than for one that dominated on many presentations.

10.00 – 10.20 Jeroen van Boxtel – Temporal form parsing dictates binocular conflict

resolution in dynamic visual stimuli A central problem in perception is how to parse a continuous stream of information into meaningful events, resolve ambiguities, and shape awareness. Presenting the eyes with incompatible images results in frequent perceptual alternations between the two eyes’ images, called binocular rivalry, allowing the investigation of the processes involved in binocular conflict resolution and the formation of awareness. A large amount of research is devoted to finding out what drives these processes, and specifically what the relative importance is of form-information compared to low-level stimulus characteristics, and motion-information. We investigated binocular conflict resolution with temporally modulated stimuli and found that rivalry between the eyes’ images may proceed even when stimulus presentations are separated by up to ~350 ms, and temporally non-overlapping in the two eyes. The data indicate that direct spatial and temporal conflict is not necessary for binocular rivalry. Furthermore, we show that the 350-ms temporal limit is independent of low-level information such as inter-ocular timing differences, contrast-reversals, stimulus energy, and eye-of-origin information. These data suggest that form information is crucial in the maintenance of rivalry, and that the temporal limit reflects the temporal grain of the visual ‘what’ or form pathway. Indeed, when systematically investigating the dependence on form versus motion information, aspects processed in the ventral and dorsal pathway respectively, we find that this temporal limit is determined by form rather than motion conflict. Our findings demonstrate that binocular conflict resolution for dynamic visual scenes depends on temporally coarse form-based processing that, likely, originates in the ventral visual pathway.

Session 8 – Of mice and men: Neuroscience in Rotterdam (Moderator: Jos van der Geest) 11.00 – 11.20 Janneke Richter - The accuracy of estimating computer work duration 11.20 – 11.40 Alexandra Badura - The role of the GABA-ergic input to Purkinje cells in

compensatory eye movements 11.40 – 12.00 Jeannette Lorteije – Inhibition and auditory processing in areas MNTB and

MSO 12.00 – 12.20 Bart van Alphen – Mouse eye movements in response to optokinetic noise

stimuli 11.00 – 11.20 Janneke Richter - The accuracy of estimating computer work duration

Computer users are generally quite bad in estimating how much time they spend working with the computer. In the curent study we investigated whether the amount of overestimation reported depends on the amount of work performed and characteristics of the users (like age, gender and the occurrence of upper extremity complaints). Results indicate that the level of overestimation indeed depends on these factors. This could potentially introduce a bias, which has large implications for understanding which riskfactors play a role in the occurrence of musculoskeletal complaints.

11.20 – 11.40 Alexandra Badura - The role of the GABA-ergic input to Purkinje cells in

compensatory eye movements As the region of the brain responsible for motor learning, the cerebellum has long been the focus of many research studies. The development of cell specific knock-out mice has made it possible to investigate each connection in the cerebellum separately by altering the expression of specific channels in the chosen cell type. Our current studies focus on the role of several types of cerebellar inhibitory interneurons, such as stellate and basket cells. To attempt at unraveling the role of these interneurons, we are performing experiments on mutant mice that selectively do not express the potassium-chloride transporter required for GABAergic inhibition in Purkinje cells. Motor reflexes are measured to determine whether these alterations have an impact on cerebellar function. The study


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of murine compensatory eye movements (vestibular-ocular and optokinetic reflex) is useful to this end, as it allows for controlled input, measurable output, and a reproducible learning pattern. By combining this behavioral data with extracellular in vivo recordings of Purkinje cell activity, we can compare the cerebellum function in wildtype and mutant mice on multiple levels. The results of these studies can contribute to a better understanding of the role of molecular layer interneurons in the cerebellum.

11.40 – 12.00 Jeannette Lorteije - Inhibition and auditory processing in areas MNTB and

MSO The medial nucleus of the trapezoid body (MNTB) and the medial superior olive (MSO) both are brainstem nuclei that process auditory information necessary for locating a sound source. MNTB is involved in processing interaural intensity differences, while MSO plays a major role in detecting interaural timing differences. Even though in vivo extracellular recordings and in vitro patch clamp recordings have been performed in both nuclei, in vivo patch clamp studies have not been made. We design experiments that enable in vivo patch clamp and extracellular recordings in these ventral brainstem nuclei in anaesthetized rodents. These recordings will address properties of MNTB and MSO neurons that cannot be studied by extracellular or in vitro studies, most importantly: • intrinsic properties (e.g. in vivo membrane potential, input resistance,

spontaneous inputs, size of IPSPs, EPSPs and spikes); • auditory processing (e.g. phase locking, frequency selectivity, maximal stimulus

repetition rate, the role of inhibitory input to MNTB and MSO, binaural interaction in MSO);

12.00 – 12.20 Bart van Alphen - Mouse eye movements in response to optokinetic noise stimuli

The optokinetic reflex (OKR) is induced by image motion across the retina and causes the eye to move in the same direction, thus minimizing retinal slip. Together with the vestibulo ocular reflex (VOR), these two reflexes are very efficient in stabilizing the retinal image over a wide range of velocities and frequencies. Both VOR and OKR have been shown to be remarkably plastic throughout life, making the interaction between VOR and OKR a popular paradigm to study cerebellar learning. We investigated the OKR in mice. Visual stimuli were created using a projector that projected an array of dots around the mice, creating a panoramic visual stimulus. We used both classical sinusoidal stimuli and lowpass filtered noise stimuli in which the array of dots moved in an unpredictable way with a homogeneous velocity distribution. The eye movements evoked by this stimulation were recorded using an infrared video system and further analyzed. Additionally, in order to investigate the role of the cerebellum in response to noisy stimuli we compared the oculomotor behavior of wildtype mice with that of the Lurcher mutant, in which the cerebellum is effectively disconnected from the rest of the brain. Since sinusoidal stimuli are predicatable, unlike noise, a putative role of the cerebellum for the temporal integration of slip signals would predict that the response to noise in the Lurcher is relatively spared. However, Lurcher mutants displayed much lower gains, both for sinusoidal and noise stimulation.


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Abstracts Posters Christiaan Stronks - Combined electric and acoustic stimulation in the cochlea of the guinea pig Patients with severe to profound high-and mid-frequency hearing loss, but residual low-frequency hearing are nowadays considered as potential candidates for cochlear implantation (Kiefer et al., Audiol Neurotol 2005). Preservation of residual hearing can improve speech intelligibility and esthetic value of sounds after implantation. However, the improvement by the addition of a hearing aid to a cochlear implant is variable (Gantz et al., Laryngoscope 2005). This raises the issue of how electric and acoustic cochlear stimulation interact. In this study the effects of ipsilateral electric stimuli on acoustically evoked cochlear potentials were examined using a forward masking paradigm. In anesthetized guinea pigs, extracochlear stimulation electrodes were placed on the round window and on, or near, the basal turn. Recording electrodes were placed on the apex of the cochlea and on the bulla wall. Acoustically evoked compound action potentials (CAPs) were recorded in response to 0.5-16 kHz tone bursts. The masker was presented as a train of 10 biphasic, alternating pulses at 1 kHz preceding the tone burst. Electric masking reversibly reduced the amplitude of acoustically evoked CAPs. Masking increased with higher electric current levels and shorter masker-to-probe intervals. Masking was more pronounced at higher acoustic stimulus frequencies (8 and 16 kHz), and became relatively stronger at lower acoustic stimulus levels. At high acoustic frequency and low acoustic level, the observed amount of masking could be as high as 90%, while CAP latency increased by no more than 0.2 ms. CAPs elicited by lower acoustic stimulus frequencies were hardly affected by electric stimulation, probably due to the fact that the electric masker was presented basally on the cochlea. These results support the idea that high frequency regions can be stimulated electrically without affecting low frequency hearing, by limiting the use of apical electrodes in conventional implants, or by using short implants (Gantz and Turner, Acta Otolaryngol 2004). Denise de Grave - Effects of the Brentano illusion on pointing movements with the left and right hand In the debate about whether illusions affect hand movements, most studies investigated illusion effects on the right hand. However, visual illusions have different effects on the hemispheres in the brain, with the right hemisphere being more affected than the left one (e.g. Weidner & Fink, 2006). As the left hand is mainly controlled by the right hemisphere, the left hand might show a larger illusion effect than the right hand. In contrast, if the left and right hand use the same information to perform a task, there is no reason for the illusion effects to differ between the hands. In this study we used the Brentano illusion to examine whether movements of the left and the right hand are equally susceptible to visual illusions. Subjects made pointing movements with their left and right hand between the arrowheads of the Brentano illusion. The illusion influenced the left and the right hand to the same extent. We conclude that there is no fundamental difference in susceptibility to the illusion between the hands. Jacob Duijnhouwer - An additional position bias in an illusory transformation of optic flow fields When an expanding and a uniform optic flow fields are transparently superimposed, the focus of expansion appears shifted in the uniform flow direction (Duffy and Wurtz, 1993). This is known as the optic flow illusion (OFI). The OFI has been interpreted as a result of the compensation for eye movements, a mechanism that might be superfluously triggered by the uniform flow. It has also been suggested that the effect is due to motion induction between abutting dots of the two flow fields. Here, we look into an alternative explanation based on motion induced position shifts (MIPS) acting on the position signal of the focus of the flow field. To distinguish a potential MIPS effect from the two existing explanations, we replaced the expanding flow field by contracting and rotating ones. The two existing explanations of the OFI predict that the focus of a contracting flow field would shift in the opposite direction of the uniform flow, and that the focus of a rotational flow field would shift perpendicular to the uniform flow. The MIPS explanation, on the other hand, predicts that the focus will perceptually shift in the direction of the uniform flow, regardless of the flow type. We find that the foci of rotational flow fields shift both perpendicular and parallel to the uniform flow. The focus of contraction shift is opposite to the focus of expansion shift, but with much reduced magnitude. These results match well with the idea that the MIPS effect plays a role in the OFI, in addition to one or both of the existing explanations. Furthermore, because the position signal of a flow field focus can only develop after the integration of the local motion signals, we think these findings provide an example of the combination of motion and position signals at a relatively high level in the visual system.


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Jeroen Benjamins - Temporal properties of task-irrelevant events: attentional capture is not purely bottom-up The ongoing debate whether attentional capture is stimulus driven or top-down modulated has recently focused on the temporal properties of task-irrelevant events leading to attentional capture. Two recent studies have proposed that attentional capture occurs when the task-irrelevant event is either temporally unique (Von Mühlenen et al., 2005) or when its occurrence is unexpected (Lamy, 2005). In the latter case expected task-irrelevant events are top-down suppressed. Here we show that attentional capture by task-irrelevant events depends on the timing of task-relevant events (target onset). Before task-relevant events occur, task-irrelevant events can be ignored. But, once the task-relevant event has occurred, task-irrelevant events do influence our percept. Task behavior seems to be split up in a waiting mode and a searching mode with different susceptibility to attentional capture. This suggests that attentional capture is not purely bottom-up, but is mediated by top-down processes as well. Joke Baas - Effects of D-cycloserine and the CB-1 agonist Δ9-THC on the extinction of conditioned fear in humans Cannabis and other cannabinoid CB-1 receptor agonists are well known for their disruptive effects on cognition. However, recent animal research has indicated that endogenous cannabinoids form a crucial factor in the extinction of learned fear responses, which suggests that agonists may also enhance processes that are important in the treatment of certain anxiety disorders. Specifically, administration of drugs that increase CB1 transmission has been shown to facilitate the extinction of conditioned fear in rodents. Several clinical trials have shown that the partial NMDA agonist D-cycloserine (DCS) facilitates extinction of phobic fears in exposure therapy. In this study, it was investigated whether a CB1 agonist (Δ9-tetrahydrocannabinol; THC) could also improve the extinction of conditioned fear in healthy human subjects in comparison to DCS and placebo. Participants received capsules containing either 10 mg of synthetic THC (Marinol, N=18), DCS (N=18), or placebo (N=18) 2 hours before extinction training. Different phases of fear conditioning (acquisition, extinction and extinction retention) took place on different days to reduce carryover effects of the drug treatments. During conditioning, fear was measured using skin conductance, fear potentiated startle and subjective measurements and conditioned responding was defined as the difference between responses to CS+ and CS-. Both groups showed a comparable conditioned response on all measures after the acquisition session. Throughout the extinction session, the THC group showed a smaller conditioned response compared to the placebo group as measured by startle (marginally significant) and first interval skin conductance responses. Two days later, the difference between groups continued to be present in the startle data during extinction retention. There were no significant effects of DCS, which is in line with other recent studies in healthy human volunteers that indicate a lack of room for improvement of the NMDA-mediated extinction process in healthy subjects. These are the first results that suggest a role of the cannabinoid system in the extinction of conditioned fear in humans. Martijn Agterberg - Quantitative analysis of surviving spiral ganglion cells in BDNF-treated cochleas of deafened guinea pigs Electrical stimulation and application of exogenous neurotrophins can enhance spiral ganglion cell (SGC) survival in deafened animals. Shepherd et al. (2005) have also observed that average SGC size in cochleas treated with brain-derived neurotrophic factor (BDNF) is larger than in cochleas of normal hearing guinea pigs. In this study, we have performed quantitative analyses of the SGCs at the light-microscopical (packing densities) and ultrastructural level (perikaryal area, nuclear area) in deafened guinea pigs after delayed neurotrophic treatment. Guinea pigs were deafened by means of co-administration of kanamycin and furosemide. The functional effect of the deafening technique was confirmed by measuring the auditory brainstem responses (ABRs). Two weeks after deafening, the right cochleas were implanted with an electrode and cannula, which was attached to an Alzet mini-osmotic pump filled with BDNF (100 µg/ml). BDNF was infused into the cochlea over a period of four weeks. Left cochleas were not treated with BDNF and served as controls. Six weeks after deafening, both left and right cochleas were fixed and processed for ultrastuctural examination and quantitative analysis. Data were compared with those obtained from normal hearing animals. SGC packing densities in the right (BDNF-treated) cochleas were 2-3 times higher than in the left (non-treated deafened) cochleas. Delayed BDNF treatment (right cochleas) resulted in a significant increase in the average SGC perikaryal area as compared to non-treated deafened (left) cochleas. These data confirm Shepherd’s findings. Martijn Schonewille - Interneurons in the molecular layer of the cerebellum are required for consolidation of motor learning Over the past decades studies on cerebellar motor learning have been mainly focused on possible roles of plasticity at the excitatory parallel fiber to Purkinje cell synapse. Here we studied the role of the inhibitory input from stellate cells and basket cells onto Purkinje cells.


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To this end we created and tested a mouse mutant in which the GABAA-receptor subunit γ2 was selectively deleted from Purkinje cells (L7-γ2 mice). Purkinje cells from homozygous L7-γ2 mice lack GABAA receptor-mediated inhibitory postsynaptic currents. Surprisingly, L7-γ2 mice show a relatively normal motor performance in that they are not ataxic and that the gain and phase values during the vestibulo-ocular reflex and optokinetic reflex are only mildly affected. Moreover, the simple spike and complex spike firing frequencies and patterns appear unaffected during the optokinetic reflex. In contrast, the L7-γ2 mice were not able to reverse the gain of their vestibulo-ocular reflex during a multiple day visuo-vestibular training paradigm. Most prominently, they were unable to consolidate their adapted gain values in between training sessions. These data indicate that the inhibitory interneurons in the molecular layer of the cerebellum are dispensable for general motor performance, but instead appear essential for the consolidation of cerebellar motor learning. Michiel Vermaak-Towards an objective diagnostic test for cerebral visual impairment Cerebral Visual Impairment (CVI) is caused by a disorder or multiple disorders in the cerebral visual tracks and/or cerebral visual processing area’s. Those disorders are nowadays mostly caused by brain haemorrhages in premature born children and perinatal asphyxia. Other causes are asphyxia as a result of near drowning, trauma or meningitis/encephalitis. The term “CVI” contains a wide variety of pathology in the cerebral processing of visual information. It may also affect a child’s cognitive and perceptual development. The majority of children with CVI also have intellectual disabilities (ID) resulting from the same aetiology mentioned earlier. As a result they may not be able to cooperate in lengthy and (for them) difficult neuropsychological testing. Being aware of a person’s visual capacities and functional problems can greatly improve communication and quality of life. An early diagnosis, preferably before the age of 2 years, also may be of paramount importance for children with CVI to optimally stimulate the development of cognitive visual processing. Therefore a quick and objective diagnostic test that can be used in (very) young children and in children and adults with ID is needed. Because eye and head movements are sensitive indicators for the processing of visual information, we are investigating a new way to diagnose specific cerebral visual processing disorders by presenting visual stimuli which specifically impinge on specific cerebral visual pathways and functions. Those visual stimuli will be combined with a (user friendly) video based head and eye movement recording system which will enable us to objectify visual function in CVI patients. Rob van Beers - Recalibration of arm movement planning Planning of a goal-directed arm movement is a difficult task for our brain because an arm is a complicated mechanical system with many muscles. As a result, movement planning is generally inaccurate, resulting in movement errors. To avoid large reaching errors, the movement planning system uses errors in previous movements to adjust planning of future movements. However, determining such a correction is not trivial because the movement planner does not know to what extent a previous error resulted from inaccurate planning and to what extent from noise in the motor system. It is generally assumed that a correction consists of an adjustment of the aim point, the point where a movement would end if there were no motor noise. Here we show that the human arm movement planning system does not make corrections relative to the aim point of the previous movement, but relative to its actual endpoint. In this way, the ambiguity about the origin of the error is irrelevant, so that movement planning can have maximal accuracy. To make this mechanism possible, the movement planning system must have access to a copy of the previous movement’s actual motor commands, i.e., the commands including the noise in that particular movement. This mechanism is near optimal in the sense of minimizing the expected movement error. Titia Gebuis - Of colored numbers and numbered colors: interactive processes in grapheme-color synesthesia Grapheme-color synesthetes experience a specific color when they see a number but they do not experience a number when a color is perceived. In this study, we investigate whether color can still evoke number-processes even when a vivid number experience is absent. We used color-number and number-color priming, both revealing faster responses in congruent compared to incongruent conditions. A numerical distance effect was present only in the color-number priming experiment. A more indirect parity judgment experiment, in which synesthetes had to judge the parity of a colored number revealed faster responses in parity congruent compared to parity incongruent trials. The results of both experiments demonstrate that synesthesia is indeed bi-directional and, more importantly, illustrate the precise nature of the interaction between color and number, and that the direction of this interaction is determined by task demands, not the more vividly experienced aspect of the stimulus.


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Tobias Borra - Orientation matching depends on the point of rotation Vertical and horizontal object orientations are perceived more accurately than oblique orientations (the oblique effect). If observers have to rotate a test stimulus to the same orientation as a reference stimulus, does the location of the point of rotation influence matching accuracy? First we established orientation matching accuracy for a two-dot stimulus rotating around it’s center of mass. Results show a standard oblique effect: high orientation matching for 0°, and lower orientation matching for 15°, 30° and 45°. In the second experiment the same two-dot stimulus was used, but the point of rotation was set so that the two dots and the point of rotation together form an imaginary rectangled triangle (with angles of 30°, 60° and 90°). Results show that orientation matching for the 30° condition improves dramatically as a result of this shift of the point of rotation, compared with the 30° condition from experiment 1. In an orientation matching task, performance is influenced by the location of the point of rotation, even though physical stimulus orientations are identical in both experiments. Hubert Fonteijn - Probabilistic Q-Ball Imaging DTI has been proven to be very useful for elucidating white matter structure in vivo. It is however limited in its capacity to resolve more than one fibre direction per voxel. Q-Ball Imaging was therefore proposed as an alternative, which focuses on the Orientation Distribution Function (ODF), which is formed by the radial integration of the diffusion probability function. Tuch has shown that measurements on a sphere in Q-Space are related to this ODF by the Funk-Radon transform. Anderson and Hess et al. have furthermore proven that this transform can be reformulated as an analytical relationship between the Spherical Harmonics (SH) coefficients of the signal and the SH coefficients of the ODF. In this abstract, we use this formulation in a Bayesian framework, to determine which order of Spherical Harmonics is appropriate to describe the diffusion-weighted signal in each voxel and to get an estimate of the uncertainty about the fibre directions, derived from Q-Ball Imaging. Good performance is shown in voxels which are hypothesized to contain more than one fibre population.


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proceedings of the 4 helmholtz retreat...proceedings of the fourth helmholtz retreat 13-15 june 2007...

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