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Philippe G Schyns

Publications and source records attributed to Philippe G Schyns.

At least 19 recordsLinked to original sources
PubMed2006

Channel surfing in the visual brain.

Vision provides us with an ever-changing neural representation of the world from which we must extract stable object categorizations. We argue that visual analysis involves a fundamental interaction between the observer's top-down categorization goals and the incoming stimulation. Specifically, we discuss the information available for categorization from an analysis of different spatial scales by a bank of flexible, interacting spatial-frequency (SF) channels. We contend that the activity of these channels is not determined simply bottom-up by the stimulus. Instead, we argue that, following perceptual learning a specification of the diagnostic, object-based, SF information dynamically influences the top-down processing of retina-based SF information by these channels. Our analysis of SF processing provides a case study that emphasizes the continuity between higher-level cognition and lower-level perception.

Brain↗
PubMed2006

The interplay between perceptual organization and categorization in the representation of complex visual patterns by young infants.

The relation between perceptual organization and categorization processes in 3- and 4-month-olds was explored. The question was whether an invariant part abstracted during category learning could interfere with Gestalt organizational processes. A 2003 study by Quinn and Schyns had reported that an initial category familiarization experience in which infants were presented with visual patterns consisting of a pacman shape and a complex polygon could interfere with infants' subsequent good continuation-based parsing of a circle from visual patterns consisting of a circle and a complex polygon. However, an alternative noninterference explanation for the results was possible because the pacman had been presented with greater frequency and duration than had the circle. The current study repeated Quinn and Schyns's procedure but provided an equivalent number of familiarization trials and duration of study time for the infants to process the pacman during initial familiarization and the circle during subsequent familiarization. The results replicated the previous findings of Quinn and Schyns. The data are consistent with the interference account and suggest that a cognitive system of adaptable feature creation can take precedence over organizational principles with which a perceptual system comes pre-equipped.

Cognition↗
PubMed2006

Perceptual moments of conscious visual experience inferred from oscillatory brain activity.

Transient periods of synchronized oscillating neuronal discharges in the brain have been proposed to support the discrete perceptual moments underlying conscious visual experience. However, the information content of these perceptual moments remains a critical challenge to the understanding of consciousness. We uncovered this information content in four observers who consciously perceived each interpretation of the ambiguous Dali painting Slave Market with the Disappearing Bust of Voltaire. For each individual observer, we isolated the stimulus spatial frequency (SF) features underlying their overt judgments of the input as "the nuns" and "Voltaire". Every 2 ms between stimulus onset and overt response, we derived the sensitivity of the observer's oscillatory brain activity (in the theta, alpha, and beta bandwidths) to these SF features. Then, in each bandwidth, we estimated the moments (between stimulus onset and perceptual judgment) when perception-specific SF features were maximally integrated, corresponding to perceptual moments. We show that the centroparietal beta oscillations support perceptual moments underlying the conscious perception of the nuns, whereas theta oscillations support the perception of Voltaire. For both perceptions, we reveal the specific information content of these perceptual moments.

Behavior↗
PubMed2005

Early selection of diagnostic facial information in the human visual cortex.

There is behavioral evidence that different visual categorization tasks on various types of stimuli (e.g., faces) are sensitive to distinct visual characteristics of the same image, for example, spatial frequencies. However, it has been more difficult to address the question of how early in the processing stream this sensitivity to the information relevant to the categorization task emerges. The current study uses scalp event-related potentials recorded in humans to examine how and when information diagnostic to a particular task is processed during that task versus during a task for which it is not diagnostic. Subjects were shown diagnostic and anti-diagnostic face images for both expression and gender decisions (created using Gosselin and Schyns' Bubbles technique), and asked to perform both tasks on all stimuli. Behaviorally, there was a larger advantage of diagnostic over anti-diagnostic facial images when images designed to be diagnostic for a particular task were shown when performing that task, as compared to performing the other task. Most importantly, this interaction was seen in the amplitude of the occipito-temporal N170, a visual component reflecting a perceptual stage of processing associated with the categorization of faces. When participants performed the gender categorization task, the N170 amplitude was larger when they were presented with gender diagnostic images than with expression-diagnostic images, relative to their respective non-diagnostic stimuli. However, categorizing faces according to their facial expression was not significantly associated with a larger N170 when subjects categorized expression diagnostic cues relative to gender-diagnostic cues. These results show that the influence of higher-level task-oriented processing may take place at the level of visual categorization stages for faces, at least for processes relying on shared diagnostic features with facial identity judgments, such as gender cues.

Adult↗
PubMed2005

Accurate statistical tests for smooth classification images.

Despite an obvious demand for a variety of statistical tests adapted to classification images, few have been proposed. We argue that two statistical tests based on random field theory (RFT) satisfy this need for smooth classification images. We illustrate these tests on classification images representative of the literature from F. Gosselin and P. G. Schyns (2001) and from A. B. Sekuler, C. M. Gaspar, J. M. Gold, and P. J. Bennett (2004). The necessary computations are performed using the Stat4Ci Matlab toolbox.

Classification↗
PubMed2005

Retinotopic sensitisation to spatial scale: evidence for flexible spatial frequency processing in scene perception.

Observers can use spatial scale information flexibly depending on categorisation task and on their prior sensitisation. Here, we explore whether attentional modulation of spatial frequency processing at early stages of visual analysis may be responsible. In three experiments, we find that observers' perception of spatial frequency (SF) band-limited scene stimuli is determined by the SF content of images previously experienced at that location during a sensitisation phase. We conclude that these findings are consistent with the involvement of relatively early, retinotopically mapped, stages of visual analysis, supporting the attentional modulation of spatial frequency channels account of sensitisation effects.

Adult↗
PubMed2005

Applying bubbles to localize features that control pigeons' visual discrimination behavior.

The authors trained pigeons to discriminate images of human faces that displayed: (a) a happy or a neutral expression or (b) a man or a woman. After training the pigeons, the authors used a new procedure called Bubbles to pinpoint the features of the faces that were used to make these discriminations. Bubbles revealed that the features used to discriminate happy from neutral faces were different from those used to discriminate male from female faces. Furthermore, the features that pigeons used to make each of these discriminations overlapped those used by human observers in a companion study (F. Gosselin & P.G. Schyns, 2001). These results show that the Bubbles technique can be effectively applied to nonhuman animals to isolate the functional features of complex visual stimuli.

Animals↗
PubMed2005

Transmitting and decoding facial expressions.

This article examines the human face as a transmitter of expression signals and the brain as a decoder of these expression signals. If the face has evolved to optimize transmission of such signals, the basic facial expressions should have minimal overlap in their information. If the brain has evolved to optimize categorization of expressions, it should be efficient with the information available from the transmitter for the task. In this article, we characterize the information underlying the recognition of the six basic facial expression signals and evaluate how efficiently each expression is decoded by the underlying brain structures.

Adult↗
PubMed2004

Scale invariant adaptation in fusiform face-responsive regions.

Several functional neuroimaging studies have observed response adaptation in face-sensitive regions when repeating identical face stimuli. To address whether this was due to low-level stimulus properties or facial identity, we decomposed pictures of faces into pictures preserving only the lower or higher parts of the normal frequency spectrum. In an event-related functional neuroimaging study, pairs of such pictures were sequentially presented that showed the same or different persons in the same or different frequency bands. This factorial design allowed to separate effects related to repetition of personal identity from those related to identical stimulus properties. In a random effects group analysis, activation in the right fusiform region was affected by repetition of personal identity regardless of changing or constant spatial scale. Responses in the more medial and posterior fusiform and lingual regions adapted with repetition of the same frequency band. An analysis in regions of interest determined individually as face responsive showed that repetition decreases for the same faces in fusiform face-responsive regions generalized across spatial frequency bands. Our results therefore point to a role of this area in discriminating individual faces at a level of representation that is invariant to changes in low-level stimulus properties, as spatial scale. The same invariance could not be detected in more posterior occipital face-responsive regions.

Adaptation, Physiological↗
PubMed2004

No troubles with bubbles: a reply to Murray and Gold.

Murray and Gold discuss two "shortcomings" of the Bubbles method [Vision Research 41 (2001) 2261]. The first one is theoretical: Bubbles would not fully characterize the LAM (Linear Amplifier Model) observer, whereas reverse correlation would. The second "shortcoming" is practical: the apertures that partly reveal information in a typical Bubbles experiment would induce atypical strategies in human observers, whereas the additive Gaussian white noise used by Murray and Gold (and others) in conjunction with reverse correlation would not. Here, we show that these claims are unfounded.

Humans↗
PubMed2004

Receptive fields for flexible face categorizations.

Abstract-Examining the receptive fields of brain signals can elucidate how information impinging on the former modulates the latter. We applied this time-honored approach in early vision to the higher-level brain processes underlying face categorizations. Electroencephalograms in response to face-information samples were recorded while observers resolved two different categorizations (gender, expressive or not). Using a method with low bias and low variance, we compared, in a common space of information states, the information determining behavior (accuracy and reaction time) with the information that modulates emergent brain signals associated with early face encoding and later category decision. Our results provide a time line for face processing in which selective attention to diagnostic information for categorizing stimuli (the eyes and their second-order relationships in gender categorization; the mouth in expressive-or-not categorization) correlates with late electrophysiological (P300) activity, whereas early face-sensitive occipito-temporal (N170) activity is mainly driven by the contralateral eye, irrespective of the categorization task.

Brain↗
PubMed2003

A principled method for determining the functionality of brain responses.

A challenging issue in relating brain function to perception and cognition concerns the functional interpretation of brain responses. For example, while there is agreement that the N170 component of event-related potentials is sensitive to face processing, there is considerable debate about whether its response reflects a structural encoder for faces, a feature (e.g. eye) detector, or something else. We introduce a principled approach to determine the stimulus features driving brain responses. Our analyses on two observers resolving different face categorization tasks (gender and expressive or not) reveal that the N170 responds to the eyes within a face irrespective of task demands. This suggests a new methodology to attribute function to different components of the neural system for perceiving complex stimuli.

Brain↗
PubMed2003

Attention enhances feature integration.

Perceptual processing delays between attribute dimensions (e.g. color, form and motion) [Proceedings of the Royal Society of London Series B 264 (1997) 1407] have been attributed to temporal processing asynchronies resulting from functional segregation of visual information [Science 240 (1988) 740]. In addition, several lines of evidence converge to suggest that attention plays an important role in the integration of functionally processed information. However, exactly how attention modulates the temporal integration of information remains unclear. Here, we examined how attention modulates the integration of color and form into a unitary perception. Results suggest that attending to the location of an object enhances the integration of its defining attributes by speeding up the perceptual processing of each attribute dimension. Moreover, the perceptual asynchrony between attributes remains constant across attended and unattended conditions because attention seems to offer each processing dimension an equal processing advantage.

Attention↗
PubMed2003

Expectancy effects on spatial frequency processing.

We explored top-down modulation of spatial frequency (SF) processing. When auditory pre-cueing directed observers' attention to one of two 4-octaves (SF) apart plaid components observers tended to perceive the cued component, suggesting selective attention to the SF channel they expected to carry task relevant information. In agreement, pre-cueing had no effect with components often processed by the same channel (0.5-octaves apart). Further, effects of expectancy were greater than of uncertainty and were SF tuned. Combined our findings suggest top-down modulation of early, cortical, SF processing. We argue this could similarly explain the previously reported influences of categorisation on SF processing.

Contrast Sensitivity↗
PubMed2003

Superstitious perceptions reveal properties of internal representations.

Everyone has seen a human face in a cloud, a pebble, or blots on a wall. Evidence of superstitious perceptions has been documented since classical antiquity, but has received little scientific attention. In the study reported here, we used superstitious perceptions in a new principled method to reveal the properties of unobservable object representations in memory. We stimulated the visual system with unstructured white noise. Observers firmly believed that they perceived the letter S in Experiment 1 and a smile on a face in Experiment 2. Using reverse correlation and computational analyses, we rendered the memory representations underlying these superstitious perceptions.

Adult↗
PubMed2002

RAP: a new framework for visual categorization.

Cognitive science might almost be defined as several disciplines communicating their different perspectives on the mind, the common object of study. However, domain-specific concepts and techniques can prevent, rather than foster, a communication of viewpoints. In this article, we develop a new framework for visual categorization in which the interaction between Represented (R) information and Available (A) information determine the Potent (P) information (symbolically, R ? A approximately P). We argue and illustrate that this framework helps to establish a common language to articulate issues common to low-, mid-, and high-level vision. More importantly, we present new techniques with which to visualize the so-far elusive constructs of representation and potent information.

Journal Article↗
PubMed2002

Understanding Dali's Slave market with the disappearing bust of Voltaire: a case study in the scale information driving perception.

A generic problem in vision is to know which information drives the perception of a stimulus. We address this problem in a case study that involves the perceptual reversal of an ambiguous image (here, Dali's painting the Slave Market with the Disappearing Bust of Voltaire 1940). In experiment 1, we use 'bubbles' (Gosselin and Schyns, 2001 Vision Research 41 2261-2271) to disambiguate the image and to determine the specific visual information that drives each possible perception (here, the nuns versus the bust of Voltaire). Experiment 2 validates that this information does determine the selective perception of the ambiguous image. We adapted the spatial-frequency channels of observers selectively to the information that mediates one of the two perceptions, to induce the opposite perception of the ambiguous image in a transfer phase. Together, the results suggest a method of revealing the visual information that drives perception.

Art↗