Ecological visuomotor tasks during prism adaptation cause larger aftereffects than repeated pointings in healty participants

Elena Calzolari, Paola Fortis, Roberta Ronchi, Marcello Gallucci and Giuseppe Vallar

Prism adaptation (PA) is an effective procedure for improving spatial neglect (Rossetti et al, 1998, Nature, 395(6698), 166-169). Recently, an ecological PA protocol (Fortis et al, 2010, Neuropsychology, 24(6), 681-697) was developed, consisting in executing visuomotor activities manipulating daily-life objects. This approach, combined with the classic repeated pointing method (Frassinetti et al, 2002, Brain, 125(3), 608-623), provided encouraging results in a recent study in right-brain-damaged patients with left neglect. Here, we compared the two paradigms in young and elderly healthy participants, to assess putative similarities and differences in producing adaptation and aftereffects. Participants underwent PA in two consecutive days, in which they performed the two tasks. In pre- and post-exposure sessions, participants performed three 'straight-ahead' tasks (proprioceptive, visual, visuo-proprioceptive). Results showed adaptation to both treatments. Interestingly, the 'ecological approach' induced greater aftereffects in the proprioceptive (young and old groups), and in the visual and visuo-proprioceptive tasks (young group only), and was rated as more enjoyable by participants. These results highlight the efficacy of the 'ecological' PA paradigm, which appears to be more effective than the traditional pointing procedure in bringing about aftereffects, whose size appears to be related to the PA-induced improvement of neglect.

Filling-in with Afterimage after MIB without Adaptation while MIB

Ryo Shohara, Makoto Katsumura and Seiichiro Naito

Introduction: The Motion Induced Blindness (MIB) is supposed that its origin is V2 or higher and MIB is independent of V1 adaptation. We examined a simple and undeniable justification that the filled-in luminance or color by MIB never led any adaptation. Methods: On the red background the 8 yellow filled circles with 3.5 degree diameter were arranged at 10 degree diameter circle periphery. Each of the yellow circles was disappeared in turn in a rotation manner by MIB. (1) We conducted the prolonged observation of filling-in color, while MIB we examined whether any aftereffects or adaptations were perceived. (2) The half of the targets remained appeared without MIB. After prolonged observation, we examined the afterimages whether any difference between MIB and no-MIB areas was perceived. Results: (1) We perceived the red filling-in color which was exactly the same to the background and never changed while prolonged observation. (2) We perceived exactly the same afterimage for the no-MIB and MIB area, one was always a real yellow, the other was the half chance of the yellow and the other half chance of filled-in red. Conclusions: Filling-in by MIB was at least at the higher visual area than the adaptation was relevant.

MIB and Filling-in with Transient Change of Background, Target or Both

Makoto Katsumura, Ryo Shohara and Seiichiro Naito

Introduction: The conventional Motion Induced Blindness (MIB) requires that the background and target should be unchanged for maintaining adaptation while the inducing texture is moving. (1) We changed the background or target luminance and color at the moment of disappearance and examined MIB. (2) We changed the background while the target was invisible by MIB such a way that after the black background adaptation, at the moment of disappearance the background was changed to dark yellow then, while MIB, it tuned to be blue then black again. We examined MIB, if not destroyed, what percepts were obtained. The findings suggested the novel independence of the adaptation for filling-in of MIB. Methods: The two white stationary filled circles with 6.5 degree of diameter were presented at 8 degree upper and lower of the center fixation point. The 5 white concentric rings appeared at the border of the circle and expanded to 8 degree radius consecutively and disappear at 8 degree radius in 1000ms, in an alternating manner at the upper or lower circle. Results: We perceived the newly changed background color after disappearance for all experiments. Conclusions: MIB and Filling-in did need the fixation, but not necessarily needed the adaptation.

Top-down control modulates face aftereffects

Pamela Pallett, Donald MacLeod and Ming Meng

Adaptation is often coined the psychophysicist's electrode. Accordingly, studies of face aftereffects indicate that face processing relies upon norm-based coding mechanisms. Here we tested whether face aftereffects are influenced by top-down control or purely bottom-up driven. Participants discriminated differences in typicality and eye-to-mouth distance while adapted to either a vertically compressed or vertically elongated face. Notably the stimuli and procedure were identical for both tasks, thus the only variable was top-down in nature (i.e., task type). As expected, we observed significant aftereffects for the typicality judgments. Adaptation to the compressed face produced a perceived 'normal' that was more compressed than the original, undistorted face. Similarly, adaptation to the elongated face produced a perceived 'normal' that was more elongated than the original, undistorted face. By contrast, we found no effect of adaptation on eye-to-mouth distance discrimination. This could occur if participants used analytical processing to isolate and compare the visual angles between the eyes and the mouth of each face; such a comparison should be unaffected by shifts in the perceived norm of faces. These results suggest that top-down control can produce qualitative differences in the neural encoding of faces .

Reduced face identity aftereffects in relatives of children with autism

Chiara Fiorentini, Laura Gray, Gillian Rhodes, Linda Jeffery and Elizabeth Pellicano

Autism is a developmental condition with complex etiology. To aid the discovery of genetic mechanisms, researchers are trying to identify potential endophenotypes - subtle neurocognitive traits present in individuals with autism and their 'unaffected' relatives. Relatives of individuals with autism often exhibit face processing atypicalities, which are similar in nature albeit of lesser degree, to those found in individuals with autism. However, the mechanisms underlying such atypicalities have yet to be clarified. We investigated whether atypicalities in adaptive norm-based coding of faces are present in relatives of children with autism, similar to those reported in children with autism (Pellicano et al, 2007, Current Biology, 17, 1508-1512). To test this possibility, we administered a face identity aftereffect task in which adaptation to a particular face biases perception towards the opposite identity, so that a previously neutral face (i.e., the average face) takes on the computationally opposite identity. Parents and siblings of individuals with autism showed significantly smaller aftereffects compared to parents and siblings of typically developing children, suggesting that adaptive face-coding mechanisms might be less efficient in relatives of children with autism. This finding suggests that diminished adaptive mechanisms may represent a neurocognitive endophenotype for autism.

In pursuit of afterimage perception: Interactions with eye movements and contours

Georgie Powell, Aline Bompas and Petroc Sumner

Observers have long been directed to avoid making eye movements during colour afterimage experiments, with the assumption that they suppress afterimage visibility. One hypothesis is that saccadic eye movements lead to afterimage suppression because they distinguish an illusory afterimage from a real stimulus in a way that fixation cannot. Unlike an afterimage, no real stimulus remains at the same retinal location after a saccade, providing a cue that the afterimage is not real. Thus, pursuit eye movements would be less likely to result in afterimage suppression as real objects can remain predominantly stationary on the retina when pursed. Contrary to these predictions, we found no difference in afterimage duration in conditions when observers made saccadic and pursuit eye movements and when their eyes remained fixed. We also explored whether providing an additional cue that the afterimage may be real - a surrounding luminance contour- influenced afterimage duration across eye movement conditions. Results revealed that afterimage duration in the pursuit and fixation conditions was increased by the contour to a greater extent than the saccade condition. Thus, while eye movements appear not to interact directly with afterimage perception, saccades may alter their perception by interacting with other cues known to enhance afterimages.

Race-contingent face aftereffects: A result of perceived racial typicality or racial categorisation?

O. Scott Gwinn and Kevin Brooks

Models of face perception suggest that faces are perceived with reference to face 'prototypes' or 'norms'. Research has shown that race-contingent aftereffects can be simultaneously induced using faces of two different races, distorted in opposite directions, as adaptation stimuli. Subsequently, a test face of a certain race will appear transformed in a manner consistent with the adaptation images used for that race, suggesting the existence of multiple prototypes. We examined whether race-contingent aftereffect size is predicted by levels of perceived racial typicality or by dichotomous racial categorisation. In experiment 1, faces with a range of 'morph levels'(i.e. relative contributions of Asian/Caucasian faces) were either rated on a continuous scale for Asian/Caucasian typicality, or simply categorised as Asian/Caucasian. As expected, typicality ratings showed a shallow slope (observers were sensitive to morph level over a broad range), while dichotomous racial categorisation showed a steep slope (rapid switch from categorisation as Asian-Caucasian). In experiment 2, race-contingent adaptation was assessed using test faces with various morph levels. Aftereffect size showed a shallow slope, more closely resembling racial typicality than categorisation data. This suggests that faces are not exclusively coded against one prototype, but instead the visual channels processing faces are broadly tuned.

Influence of visual illusions on some dynamic parameters of human vertical posture.

Svetlana Rychkova, Natalya Holmogorova and Galina Rozhkova

The visual system exerts both a nonspecific and a specific influence on human vertical posture. The first one depends upon the ambient illumination level. It is mediated through a modulation of the postural muscle tone. The second one depends upon the spatial interpretation of the visual input. The visual systems of internal body and external space representation are involved in the control of the reference positions and the postural reactions. We studied the influence of visual illusions on human vertical posture. The stabilograms and ballistograms were recorded in 20 young adults (aged 18-25 years) who had to maintain a vertical posture under various visual conditions. The visual stimuli included dynamic patterns that evoked the stereokinetic illusion of depth (SKI) or the illusion of ambiguous rotation (ARI). In some experiments, the subjects wore goggles producing a horizontal visual inversion (HVI). The greatest changes in the control parameters of the dynamic stabilization of the verticalposture were observed under monocular viewing conditions the case of SKI. HVI had no significant influence in the case of SKI but, in the case of ARI, was always accompanied by an increase of the dynamic indexes.

The positional motion aftereffect is spatially selective in world coordinates

Marco Turi and David Charles Burr

We measured spatiotopicity with the classical motion aftereffect (illusory motion following adaptation to motion) and the positional motion aftereffect (the change in apparent position after adaptation to motion). Subjects adapted to small (1°) vertically aligned patches of gratings (1 c/deg), drifting in opposite directions at 3 deg/sec. They saccaded 12° rightwards to a target, then test gratings (same size and spatial frequency) appeared for 500 ms, in the same retinal or the same screen position (or both, with no intervening saccade). The MAE was strictly retinotopic, but the PMAE showed a strong spatiotopic component. We also measured the PMAE with test gratings that were apparently stationary (with illusory MAE annulled) and found that under these conditions, the effects were almost entirely spatiotopic, with no statistically significant retinotopic component. Finally we measured the time required to generate a spatiotopic representation. After displaying the saccade target, we waited for a variable period before extinguishing the fixation point, the signal to saccade. For short exposure of the saccade target (300 ms) the effects were more retinotopic, for longer durations more spatiotopic. The results provide clear evidence for a spatiotopic map in humans, which takes time to build up.

Motion-form interactions beyond the motion integration level: psychophysical evidence for interactions between orientation and optic flow signals

George Mather, Rosilari Bellacosa Marotti and Andrea Pavan

Motion and form encoding is closely coupled in the visual system. A number of physiological studies have shown that neurons in the striate and extrastriate cortex (e.g., V1 and MT) are selective for motion direction orthogonal to their preferred orientation, but some neurons also respond to motion parallel to their preferred spatial orientation. Recent psychophysical research [Mather et al, 2012, Neuropsychologia, 50(1), 153-159] has demonstrated that the strength of motion adaptation is modulated by simultaneously presented orientation signals, and suggests that the interaction occurs at the level of motion integrating receptive fields in extrastriate cortex. In the present psychophysical study we investigated whether motion-form interactions take place at a higher level of neural processing where optic flow components are extracted. We measured the duration of the motion after-effect (MAE) generated by contracting or expanding dot fields in the presence of either radial (parallel) or concentric (orthogonal) counter-phase pedestal gratings. The results showed that motion adaptation (as measured with the MAE) is suppressed most by orientation signals orthogonal to optic flow direction, suggesting that motion-form interactions also take place at the level where optic flow is processed.

The role of stationary and dynamic test patterns in rapid forms of motion aftereffect

Maris Skujevskis and Andrea Pavan

Sub-second adaptations to directional motion can produce motion aftereffect (MAE). Unlike the characteristics of the classical MAE - produced by adaptations of several seconds up to minutes - the properties of the rapid form of MAE (rMAE) have been less well explored. In a series of experiments, we assessed the role of stationary and dynamic test patterns (counter-phase flickering gratings) in generating rMAE. In particular, we varied the duration, temporal frequency, and spatial phase of the adapting stimuli. Our results revealed that the strongest rMAE is produced when using dynamic test patterns. The dynamic rMAE shows a strong dependency on the adaptation duration and temporal frequency, but not on the spatial phase of the adapting pattern. In addition, similarly to the classical dynamic MAE, the temporal frequency tuning of the dynamic rMAE suggests the involvement of both low-pass and band-pass visual channels. In contrast to the dynamic rMAE, our results did not show any evidence for the static rMAE, suggesting, in addition to some recent physiological and psychophysical findings, that the static rMAE is primarily dependent on the properties of the stimuli and the specific experimental procedures employed.

Retinal and extra-retinal motion aftereffects compared

Tom C Freeman, Eleanor Boot, Helen Brown and J Rhys Davies

Recent work has shown that extra-retinal motion aftereffects (erMAE) exhibit properties that are distinctly different from retinal motion aftereffects (rMAE). In particular, adapting to reflexive eye movements produce erMAE that does not store, while oblique pursuit produces erMAE that changes direction over time. Here we provide further evidence of marked differences between erMAE and rMAE. Experiment 1: Following adaptation to pursuit or retinal motion, a small stationary test presented in complete darkness produced negligible rMAE (mean duration 0.8s) but compelling erMAE (17.2s). Conversely, when the test was surrounded by a large texture field, rMAE was now seen (4.7s) and erMAE considerably reduced (4.4s). Experiment 2: erMAE was strongly modulated by adaptation direction, with durations following horizontal pursuit at least half that following vertical pursuit. For high frequency adaptation (1Hz sawtooth wave), upward pursuit produced much longer erMAE (8.7s) than either downward (4.3s) or horizontal (2.9s). Conclusions: The reduction of erMAE by a texture field suggests that a non-retinotopic extra-retinal signal can, during MAE, be downweighted in favour of a stationary prior. On the other hand, the effects of direction on erMAE would seem to reside at an earlier stage of processing, perhaps within the oculomotor system itself.

The reference frame of the motion after effect

Niia Nikolova and Sabine Raphael

We examined the reference frame of the motion after effect to centripetally or centrifugally moving dots. The strength of the after effect was measured by matching the perceived velocities of transparently moving expanding and contracting dots in a briefly presented test (350ms). The test was always positioned in the center of the screen. In the Control-condition the fixation point, and the focus of expansion/contraction of the adapter was in the center of the screen. In the Roaming-Fixation (RF) condition the focus of the adaptor was in the center of the screen and the position of the fixation point was changed randomly along the 4deg circumference from the center of the adapter once every second. Thus any given retinal point received a mixture of adapting motion directions over time. In the Roaming-Adapter (RA) condition fixation was kept steady but the focus of expansion/contraction of the adapter changed randomly along the 4deg circumference from the fixation point once every second. Results: The strongest effect of adaptation was observed in the Control-condition. Weaker adaptation was found in the RF condition, whereas in the RA condition the effect was negligible. Conclusion: The reference frame for centrifugal and centripetal movement is not entirely spatiotopic or retinotopic.

Crossmodal adaptation aftereffects following observation of human hand actions

Stephen Page and Nick Barraclough

Repeated exposure (adaptation) to visual actions can induce adaptation aftereffects biasing subsequent perception of visual actions [Barraclough et al, 2009, Journal of Cognitive Neuroscience, 21, 1805-1819]. Crossmodal aftereffects have been observed to more simple stimuli, for example adaptation to visual motion in depth causes auditory loudness aftereffects [Kitagawa and Ichihara, 2002, Nature, 416, 172-174]. In order to investigate multimodal action coding, we tested whether action sound perception was influenced by prior adaptation to different stimuli (auditory only, visual only, or audiovisual representations of actions). After adapting to auditory action sounds (hand knocking and hand slapping), subsequent test stimuli (blended 'knock'and 'slap'sounds) sounded less like the adapting stimulus, a repulsive auditory aftereffect. This auditory aftereffect showed a characteristic increase with repetition of the adapting stimulus. We also observed significant crossmodal aftereffects following audiovisual and visual only adaptation. These high-level crossmodal aftereffects suggest multimodal coding of actions in humans, and may result from adaptation in multimodal neurons selective for actions as have been found in the monkey [Barraclough et al, 2005, Journal of Cognitive Neuroscience, 17, 377-391].

Adaptation transfer effects are moderated by the similarity to the adaptors

Stella Faerber and Claus Christian Carbon

Most studies on visual adaptation refer to adapting within identical material between adaptation and test. Here we extend the adaptation literature by systematically investigating the impact of similarity between adaptation (inspection) and test (rating) phase on the size of adaptation. To get deeper knowledge on the impact of such adaptation processes on aesthetic dimensions, we employed two important variables of aesthetic appreciation (typicality and liking) within a test-adaptation-test paradigm. We used four 3D-based models of chairs as stimulus material, varying on two design dimensions (proportion and colour saturation). Three out of the four models differed in their similarity to the adaptor chair model (transfer condition), while the fourth model was identical with the adaptor chair (no-transfer condition). As predicted we found significant adaptation effects for typicality as well as liking in the no-transfer condition. More importantly, we found adaptation effects for the transfer condition with similarity of the regarding chair model to the adaptor model being positively related to the size of the effects. These results are discussed in a theoretical framework where we propose a recalibration mechanism of the central prototype or norm within a multidimensional space framework moderated by the distance of each exemplar to the adaptor.

Effects of Perceived Strength of Illusory Contours on Tilt Aftereffects

Gurjyot Singh, Gennady Erlikhman, Tandra Ghose and Zili Liu

We examined the tilt after-effect (TAE) for illusory contour stimuli, similar to those in Paradiso, Shimojo, & Nakayama (1989, VisRes,29), where two groups of half-circles faced each other, with their arc-ends precisely aligned to form a sharp-IC ('Normal-IC'). We weakened illusory contour strength in two ways: (1) by adding randomly sized rings to the arc-ends that support the contour 'Ringed-IC', and (2) by changing the overlap between the arc-ends by a constant angle 'Perturbed-IC'. We compared TAE for these conditions to the Normal-ICs in a 2X2 design. Adaptors were oriented at 15º or -15º (0º was vertical). The test orientations were ±1º, ±1.5º, ±2º, and ±2.5º, interleaved randomly. Subjects indicated whether the test stimulus was tilted to the left or right. Subjects' perceived vertical was measured prior to adaptation. Surprisingly, the sigma (1/slope) of the fitted psychometric functions was greater for Normal-ICs than the Ringed-IC or Perturbed-IC. We also found that the magnitude of the TAEs was positively correlated with the variance of the perceived vertical. Moreover, sigma increased with adaptation for all stimuli. These results suggest that TAE magnitude is predicted by the noise of the tilt-estimation processes rather than the perceived strength of IC.

How Expectation changes the appreciation of arts.

Peter Kraemer and Claus-Christian Carbon

Information about authenticity seems to be very important in appreciating artworks due to the relevance of originality in the fine arts. To examine the influence of authenticity regarding the evaluation of arts, we exposed participants in a within-subject-design to famous pictures which were labelled as originals or copies, although both versions were physically the same. As we were mainly interested in participants'spontaneous impressions, we asked them to firstly describe the pictures verbally, followed by ratings on several explicit scales. We found evidence, that so-labelled genuine pictures were rated higher than so-labelled copies on the explicit scales of suitability of used colours, general appreciation, painter's talent and quality of the picture. Results of qualitative data analysis further indicated that genuine pictures are more appreciated due to suitability of colours. Most importantly, the qualitative analysis of the given statements pointed to important directions of the specific cognitive processes being in action when people perceive so-called 'originals' vs. 'fakes'. For instance most statements referred to colours which could mean that assumed differences among the pictures are suspected in colour in the first place. In sum, this study underlines the importance for an artwork of being unique to be evaluated as masterpiece.

The boundary conditions of priming of attentional choice: From passive viewing through task-relevant working memory load

Arni Kristjansson, Styrmir Saevarsson and Jon Driver

Priming of attentional choice has been shown to have a dominating effect upon attentional shifts and is thought to play a decisive role in visual stability between shifts. Despite this importance, the nature of the memory representations underlying priming remain controversial, and the processing necessary and sufficient for such priming to occur is not well understood. To understand more fully the necessary conditions for priming we contrasted passive versus active viewing of visual search arrays in experiment 1. There was no priming from passive viewing of search arrays, while it was strong for active search of the same exact displays. In experiment 2 we introduced working memory load during visual search in an effort to disrupt priming. The observers had to perform visual search while retaining in memory visual search arrays similar to the ones that they searched. The memorized items had either the same or different colors from the visual search items. Retaining items in working-memory abolished priming of the working-memory task-relevant colors, while interference was miniscule for unrelated colors. The picture that emerges of priming is that it requires active attentional processing of the search items in addition to the operation of visual working memory, where task-relevance of the working-memory load plays a key role.

High attentional load improves saccadic adaptation

Peggy Gerardin, Alessandro Farne and Denis Pélisson

Adaptation processes maintain saccade accuracy against various events (e.g. growth, aging, neuro-muscular lesions). The adaptation substrates for reactive and voluntary saccades (Gerardin et al., 2012) closely match the cortical substrates of exogeneous and endogeneous attention control (Corbetta and Shulman, 2002). However, it is still unknown whether attention can directly affect saccadic adaptation. To test this hypothesis, we manipulated attention during adaptation by combining a perceptual task with an adaptation double-step paradigm. During the on-going saccade, the target was simultaneously shifted (to induce adaptation) and changed into a Gabor patch of randomized orientation. Eight subjects performed, in a counterbalanced order, two adaptation sessions that only differed in the task difficulty: in the 'Easy'session subjects had to report whether the Gabor was tilted horizontally or vertically whereas in the 'Challenged'session, subjects reported whether the Gabor was slightly tilted to the left or to the right. Our results show that the build-up and retention of saccadic adaptation induced by the repetition of stepping targets were larger in the 'Challenged'than in the 'Easy'perceptual task. These results support the hypothesis that attention affects adaptation of saccades. Corbetta M, Shulman GL. 2002. Control of goal-directed and stimulus-driven attention in the brain. Nat Rev Neurosci. 3, 3: 201-215. Gerardin P, Miquée A, Urquizar C, Pélisson D. 2012. Functional activation of the cerebral cortex related to sensorimotor adaptation of reactive and voluntary saccades, accepted in NeuroImage: 10.1016/j.neuroimage.2012.03.037.

Visual search with covert adapted saccades

Annegret Meermeier, Katharina Havermann and Markus Lappe

Covert visual search may involve covert eye movement planning processes to shift attention within the search display. Saccadic adaptation is a process by which the amplitude of a saccade to a visual target is shortened, such that target location and saccade landing position become dissociated. Saccadic adaptation influences perceptual localization and perhaps deployment of attention. The present study examines the effect of saccadic adaptation on reaction times in a visual search task. The search task implied an overt and a covert condition, differing in whether the execution of saccades was allowed or not. Performance was measured by the reaction times subjects needed to find a target letter out of an array of twelve different letters. Thirteen subjects participated in an experiment consisting of a baseline measurement of search performance, a phase of saccadic adaptation, and a post-adaptation measurement of search performance. Saccadic adaptation was hypothesized to interfere with visual search resulting in elongated reaction times. In both conditions this effect of elongated reaction times after adaptation of eye movements was found. Thus saccadic adaptation indeed affects covert visual search. These findings suggest that covert saccade planning processes are involved in visual search.

Dividing attention into multiple modalities impairs the motor-visual temporal recalibration

Masaki Tsujita and Makoto Ichikawa

Prolonged exposure to fixed temporal lag between participant's keypress and visual feedback recalibrates motor-visual temporal relationship, and consequently shifts the point of subjective simultaneity (PSS) in subsequent temporal order judgments between the keypress and visual flash (Stetson et al., Neuron, 51, 651-659). In this study, we examined whether dividing attention into different sensory modalities affected the adaptive shift. In the adaptation phase, the participants constantly pressed a key accompanied by a visual feedback. We injected 0ms or 200ms fixed temporal lag between the keypress and visual feedback. In addition, we presented either of visual flashes around the fixation point or auditory beeps as targets for attention task in each block. In the test phase, the participants conducted temporal order judgment between the keypress and visual flash. If participants attended to the visual targets in the adaptation phase, PSS shifted significantly although, if they attended to the auditory targets, there was no significant shift in PSS. These results suggest that the high level cognitive processing, such as attention, plays important roles in the temporal recalibration, and that turning attention away the modality which is engaged in the motor-visual temporal relationship impairs the adaptive shift.

Lightness constancy can be enhanced by optimal exploratory gaze

Rob Lee and Hannah Smithson

We perceive the lightness of surfaces as relatively invariant across illumination conditions. The corollary of such constancy is that when the luminance of light reaching the eye from two differently reflective surfaces under differing illumination is the same the two surfaces appear different, as seen in Adelson's Checker Shadow illusion (Adelson, 1995, ion.html). The apparent similarity of these surfaces, however, depends on the amount the observer moves their gaze around the image. We measured eye-movements as observers made relative judgements of the lightnesses of reference and test probes that were superimposed on two patches with different reflectances but identical luminances. We found a relationship between the spatial extent of exploratory eye movements and the shift in the point of subjective equality when the reference was presented on one or other patch. If eye movements sample regions of the image that fall under the same simulated illumination, local adaptation with an extended time-course can produce retinal regions adapted to one or other illumination. Secondly we compared conditions in which eye movements were directed to sample across vs. within illumination regions. We analysed the observed differences between conditions in terms of an adaptation model with particular spatial and temporal summation constants.

Adaptation to binocularly fused colors

Hiroshi Yamano and Eiji Kimura

A purely binocular color system, which integrates inputs from different eyes only when the two eyes are stimulated simultaneously, has been implicated in both binocular color-mixture and adaptation studies. The former studies reported color mixture or color fusion between different colors presented dichoptically. The latter studies reported adaptation effects specific to simultaneous binocular stimulation with the same colors presented binocularly (e.g., Shimono et al., 2009, Vision Research, 49, 202-210). This study explored the relationship between the binocular color systems implicated in different conditions by investigating the adaptation effect of a binocularly fused color. Comparison was made in the adaptation effect between the simultaneous and alternating adaptation conditions. Under the simultaneous condition, red and green stimuli of 18 cd/m² were presented simultaneously to the left and right eyes, respectively, whereas under the alternating condition the same color stimuli were presented alternately to the same eyes. Color stimuli were flickered at 5 Hz to facilitate binocular fusion. We found almost identical adaptation effects under the simultaneous and alternating conditions, although observers reported stable color fusion under the simultaneous condition. These findings suggest that binocular color processing does not always produce differential adaptation effects.

Predicting categorical colour perception in successive colour constancy

Jordi Roca, C. Alejandro Parraga and Maria Vanrell

Colour constancy is a perceptual mechanism that seeks to keep the colour of objects relatively stable under an illumination shift. Experiments have shown that its effects depend on the number of colours present in the scene. We studied categorical colour changes under different adaptation states, in particular, whether the colour categories seen under a chromatically neutral illuminant are the same after a shift in the chromaticity of the illumination. To do this, we developed the chromatic setting paradigm [J Vis 2011;11:349], which is as an extension of achromatic setting to colour categories. The paradigm exploits the ability of subjects to reliably reproduce the most representative examples of each category, adjusting multiple test patches embedded in a coloured Mondrian. Our experiments were run on a CRT monitor (inside a dark room) under various simulated illuminants and restricting the number of colours of the Mondrian background to three, thus weakening the adaptation effect. Our results show a change in the colour categories present before (under neutral illumination) and after adaptation (under coloured illuminants) with a tendency for adapted colours to be less saturated than before adaptation. This behaviour was predicted by a simple affine matrix model, adjusted to the chromatic setting results.

Conformity of dichromate colour samples to colorimetry, colour appearance, and psychophysics

Sergejs Fomins, Maris Ozolinsh and Kaiva Luse

Following the characterization of printers colour reproduction, candidate samples corresponding to deuteranopy and protanopy confusion lines were printed with inkjet and photographic technology. Samples saturation changed from neutral gray to fully saturated colours with slight variations along to dichromate confusion lines. The task of colour deficient subjects was to estimate the samples for neutrality or presence of chroma under standard fluorescent (daylight, cool white fluorescent, TL84) and incandescent light sources. Samples spectral reflectance was measured and colorimetric values calculated for mentioned light sources according to ASTM 308 standard with appropriate colour matching functions. Change of illumination source produced pronounced effect on colour and neutral samples preferences of colour deficient subjects. We compared psychophysical results to the colorimetric changes due to illumination. Alternatively colour appearance models were applied to check for conformity of colorimetric values to psychophysical results. Our results showed good agreement between psychophysical evaluation of dichromate colour vision persons and colour appearance models. To model the performance of modern solid state illumination colour appearance for warm and cool LED lights was calculated.

High-level color adaptation for familiar objects

Teresa López Hernan Perez, Claus Christian Carbon and Vera Hesslinger

High-level aftereffects have mainly been researched in the domains of face and object perception to date: Exceeding mere short-term perceptual changes they also affect mental representations, e.g. of highly familiar faces for which sustained aftereffects lasting several days have been revealed [Carbon and Ditye, 2012, Frontiers in Perception Science, 3, 1-6]. With regard to color perception aftereffects are part of the classical research canon - but only on a low-vision level. To investigate higher-level aftereffects, i.e. the impact of adaptation on the mental representation of colors, we used highly familiar logos with very distinct, unambiguous color layouts like the yellow Deutsche Post emblem and the red Coca-Cola signet. Aftereffects were triggered by massive exposure to versions of these logos that had been generated by altering the hue 90 degrees (clockwise direction) away from the original one as defined by the HSB (Hue-Saturation-Brightness) color system. To ensure continuous attention participants were asked to indicate the respective orientation of these adaptors (rotated left/ upright/ rotated right). Results showed clear adaptation effects concerning the colors of the employed logos demonstrating high flexibility of the mechanism of color representation, which implicates an extension of high-level aftereffects to the domain of color perception.

The speed of adaptation as a function of eccentricity and fields luminances adaptation

Alejandro H. Gloriani, Beatriz M. Matesanz, Isabel Arranz, C. de La Rosa, Luis Issolio, José Antonio Menéndez, Alicia Galindo, Santiago Mar and Juan Antonio Aparicio

There is a growing interest in studying mesopic since in this range rods and cones are simultaneously active. It has been suggested that rods cone interactions could be responsible for alterations in temporal and spatial visual response. By employing a two-channel Maxwellian view optical system we measured thresholds luminance at a steady adapting field (LA) and a transient adapting field (SOA 300), considering retinal eccentricities between 0º and 15º, and adaptation fields from 0.06 to 100 cd/m2. We determined the speed of adaptation as the ratio between the steady and transient thresholds. We found very different functional behaviors with eccentricity for adaptation to mesopic and photopic ranges. While at mesopic levels speed increases from fovea to parafovea and decreases to peripheral retina, for photopic fields speed increases monotonically with eccentricity until 15º. We suggest that this behavior is explained by the different rod and cone distributions and its interaction. Physiology of peripheral cones could be responsible of the increase in the speed with increasing eccentricity but, at lower luminances, rod intrusion could be responsible of the velocity decrease in the peripheral retina.

Steady-state visual-evoked potential adaptation to faces is invariant to orientation, viewpoint and emotions.

Pál Vakli, Kornél Németh, Márta Zimmer and Gyula Kovács

Stimulation of the visual system at a given frequency evokes an oscillatory electrical brain response - the steady-state visual-evoked potential (SSVEP). A recent study has shown that the repetition of the same face results in the habituation of the SSVEP responses compared to a condition in which faces of different identities are presented (Rossion & Boremanse, 2011, Journal of Vision, 11, 1-21). In the present study, our goal was to investigate whether this habituation indeed reflects the recalibration of a neural population engaged in identity-specific processing. First, we could replicate previous findings of SSVEP adaptation: we found greater SSVEP amplitudes for different than for same identity faces over several right hemisphere posterior electrode sites at the stimulation frequency (4 Hz). Further, the SSVEP magnitudes did not differ between these conditions when the faces were presented upside-down, similarly to previous findings. We also observed response habituation when the same identity face was repeated while the 2D orientation or 3D viewpoint, facial expression or the shape of the internal facial features of that face changed continuously. Our results imply the adaptation of a cortical site responsible for the identity-specific representation of faces, independently of orientation, viewpoint and facial expression.

Investigating face identity perception using event-related steady-state visual evoked potentials

Joan Liu-Shuang, Anthony M. Norcia and Bruno Rossion

The perceptual mechanisms underlying humans'ability to individualise faces remain unclear. Here we extend to an event-related mode the recent application of steady-state visual evoked potentials (SSVEP) to study face identity processing [Rossion & Boremanse, 2011, JOV]. We recorded 128-channel EEG in 18 observers presented with 60-second sequences of face stimuli shown at a constant frequency of 6Hz. A 'base face identity' (A) was repeated throughout each sequence with face size randomly varying at every cycle. Different identities were introduced at fixed intervals (every 4 stimuli, or 6Hz/5=1.2Hz), resulting in the following sequence structure: AAAABAAAAC... To ensure that signal at 1.2Hz truly reflected high-level perception of identity, we manipulated orientation (upright vs. inverted, Experiment 1) and contrast (normal contrast vs. contrast reversal, Experiment 2). Both experiments showed marked increases of EEG amplitude at 1.2Hz and its harmonics (2F=2.4Hz, 3=3.6Hz...), with peak values in the right occipito-temporal channels around P8. While the basic 6Hz response was large for inverted and contrast-reversed faces, responses at 1.2Hz and its harmonics - corresponding to identity change detection - were minimal in these conditions. These observations validate the event-related SSVEP approach and prompt its use in further investigations of face identity perception in different human populations.

Adaptation to grating motion reduces pattern selectivity in area MT

Adam Kohn, Carlyn A Patterson and Stephanie C Wissig

Neuronal responses and perception are altered by adaptation, the recent history of stimulation. The hierarchical organization of the visual system, in which higher areas perform computations on input from lower areas, gives rise to distinct issues for understanding how adaptation affects visual processing. While the effects of adaptation have been seen across multiple levels of processing, little is known about how adapted input from early cortex affects computations in downstream networks. To address this issue, we recorded neuronal responses in area MT of macaque monkeys, where some neurons integrate the motion signals represented in early cortex. We find that prolonged exposure to a drifting grating, previously shown to adapt neurons in early cortex, reduces pattern selectivity in MT. A feedforward model demonstrates that changes in MT pattern selectivity can be produced by altering V1 input. Both in the model and in our data, the way in which adaptation alters MT tuning for grating motion is predictive of how pattern selectivity is affected. Grating adaptation also reduces perceived coherence of bi-stable plaids. Our findings suggest computations in higher cortical areas can be disrupted by the altered representation of low level visual features after adaptation.

Spatial specificity and inheritance of adaptation in the human visual system

Sarah Harrison and Jonas Larsson

Stimulus-selective adaptation to simple visual features such as orientation and motion direction has been observed in multiple human visual cortical areas. It is unclear to what extent this adaptation is simply inherited from V1, or whether it reflects local adaptation in extrastriate visual cortex. We used fMRI to measure the spatial specificity of orientation- and direction-selective adaptation to identify the origin of adaptation to these features. If adaptation originated in V1, we would have expected the spatial specificity of stimulus-selective adaptation to match the extent of V1 receptive fields, whereas adaptation in higher extrastriate areas with much larger receptive fields would have predicted the spatial specificity of adaptation to be correspondingly larger. Consistent with single-unit studies in macaque visual cortex, we found that nearly all of the adaptation in extrastriate visual cortex could be explained by simple downstream inheritance of V1 adaptation. For orientation-selective adaptation, there was no evidence of additional adaptation beyond V1. However, the data suggested that some proportion of direction-selective adaptation may originate in motion-responsive dorsal stream areas (MT, V3A, and V7). Interestingly our results indicated that orientation-selective adaptation, but not direction-selective adaptation, is strongly influenced by suppressive surround effects in V1.

Number adaptation does not alter BOLD signal in V1

Elisa Castaldi, David Aagten-Murphy, Michela Tosetti, David Burr and Maria Concetta Morrone

Psychophysical studies suggest that the perception of numerosity is a basic sensory attribute which is susceptible to adaptation. Previous neuroimaging studies have reported fMRI habituation signals in the intra-parietal sulcus (IPS). However, it is not clear if this result reflects the adaptation of the primary visual area. We developed a novel adaptation paradigm, wherein rapid adapting and testing stimuli can be separated by more than 20 seconds, producing strong psychophysical adaptation to number. This procedure is ideally suited to measuring BOLD adaptation with rapid event related design. Indeed it allows for temporal dissociation between activity evoked by the adaptation and test stimuli. In spite of psychophysical evidence for adaptation occurring, we did not observe any significant BOLD signal change in V1 demonstrating that the effect is not due to density. We did, however, find clear changes in BOLD activity in area IPS.

Visuomotor tracking: Minimizing visual error does not rely on visual error alone

Loes Van Dam, Dan Li and Marc Ernst

When tracking visual targets with our visible hand or a cursor, vision is the only modality that provides a direct error signal between target and cursor positions. To align cursor and target we should therefore primarily rely on visual error. However, target and cursor represent different aspects of the task: we actively control the cursor but not the target. We investigated whether sudden visual spatial discrepancies between cursor and target are treated differently depending on the respective reliabilities of the target and cursor position signals, and which of the two caused the error. By moving a stylus on a graphics tablet, participants tracked moving visual targets. In different conditions the relative reliability of target and cursor was manipulated, keeping the reliability of the visual error signal constant. If the tracking mechanism is simply minimizing the visual error, participants should adapt equally quickly to sudden changes regardless of whether the position of target or cursor was changed. Interestingly, the results show a clear difference in adaptation rate between the conditions. Partially, this can be explained by considering proprioceptive information about the movement of the hand. Our results furthermore suggest there may be differences in processing visual information for cursor and target.

Size adaptation affects the perceived size and the BOLD activation of area V1

Arezoo Pooresmaeili, Roberto Arrighi and Maria Concetta Morrone

Most perceptual properties can be affected by adaptation. In this study we show that prolonged viewing of a large, peripherally displayed stimulus causes smaller test stimulus presented to the same region to be perceived smaller than its actual size, while adaptation to a smaller stimulus causes the test to appear larger. Adaptation to a stimulus of the same size did not change perceived size. To explore the neural correlates of this effect, we measured the spatial extent of the BOLD activation of the retinotopically defined primary visual cortex (area V1). We found that the size of the activated V1 surface decreased after adaptation to a larger stimulus and increased when preceded by a smaller adapter, by comparable amounts to those observed psychophysically. Adaptation to a stimulus with the same size did not change the size of the activated V1 surface. The pattern of V1 activation closely matched the behavioral effects of size adaptation. These results corroborate recent findings showing that activity in V1 reflects the perceived size of a stimulus even when this perception is illusory and non-veridical.

Motion-direction specificity for adaptation-induced duration compression depends on temporal frequency.

Aurelio Bruno, Eugenie Ng and Alan Johnston

Adapting to a 20 Hz oscillating grating reduces the apparent duration of a 10 Hz drifting grating subsequently displayed in the same location relative to a stimulus displayed in an unadapted position. The effect is orientation-independent, as it remains for an adaptor rotated 90° relative to the tests (Johnston, Arnold & Nishida, 2006, Current Biology, 16(5), 472-479). However, at 3 Hz, duration compression follows adaptation only when adaptor and test drift in the same direction with no compression when they drift in opposite directions (Curran & Benton, 2012, Cognition, 122(2), 252-257). Here we explore direction dependence for a wider range of temporal frequencies (3-18 Hz). We first measured perceived temporal frequency for the same stimuli after adaptation and we used these estimates to match the apparent rate of the adapted and unadapted tests in the duration task. We found that, while at 3 Hz the effect of adaptation in the opposite direction on apparent duration is indeed marginal, at higher frequencies the amount of duration compression becomes substantial. These results indicate that there are probably two mechanisms at work here: one sensitive to orientation and motion direction at low temporal frequencies, and a direction-independent mechanism at higher frequencies.

Craniotopic adaptation-based changes to perceived event-duration are not accompanied by changes in perceived onset or offset of stimulus.

Tiziana Vercillo, Debora Pittelli, Guido Marco Cicchini and David Burr

Although perceived time is thought to be a supramodal perceptual dimension, recent evidence suggests that perception of duration is subserved by specialized mechanisms selective for stimulus position. A series of studies has shown that adaptation to temporal intervals occurs both in retinotopic as well as craniotopic coordinates. In the current study we reinforce the evidence for craniotopic adaptation by showing that craniotopic adapters of different speeds have opposite effects on perception of duration: adaptation at 20 Hz causes the duration of a 600 ms, 10 Hz test to be underestimated, while a 5 Hz craniotopic adapter causes overestimation of the duration of the 10 Hz test. The difference in perceived duration after separate high- and low-frequency adaptation was 85 ms, consistent across subjects. To control for attention and salience we measured (with an acoustic temporal-order judgment) the perceived onset and offset of the visual test stimulus, and found that neither were affected by adaptation. The results reinforce evidence for craniotopic adaption-induced mechanisms of event duration, and further reinforce suggestions that event duration is measured by different mechanisms than those that measure event onset and offset.