•  39
    Although symmetry has been discussed in terms of a major law of perceptual organization since the early conceptual efforts of the Gestalt school (Wertheimer, Metzger, Koffka and others), the first quantitative measurements testing for effects of symmetry on processes of Gestalt formation have seen the day only recently. In this study, a psychophysical rating study and a “foreground”-“background” choice response time experiment were run with human observers to test for effects of bilateral symmet…Read more
  •  100
    Colour for behavioural success
    I-Perception 2 (9): 1-23. 2018.
    Colour information not only helps sustain the survival of animal species by guiding sexual selection and foraging behaviour but also is an important factor in the cultural and technological development of our own species. This is illustrated by examples from the visual arts and from state-of-the-art imaging technology, where the strategic use of colour has become a powerful tool for guiding the planning and execution of interventional procedures. The functional role of colour information in term…Read more
  •  110
    Evolution and geometry generate complexity in similar ways. Evolution drives natural selection while geometry may capture the logic of this selection and express it visually, in terms of specific generic properties representing some kind of advantage. Geometry is ideally suited for expressing the logic of evolutionary selection for symmetry, which is found in the shape curves of vein systems and other natural objects such as leaves, cell membranes, or tunnel systems built by ants. The topology a…Read more
  •  18
    Perceptual Categories Derived from Reid’s “Common Sense” Philosophy
    with Adam Reeves
    Frontiers in Psychology 8. 2017.
    The 18th-century Scottish ‘common sense’ philosopher Thomas Reid argued that perception can be distinguished on several dimensions from other categories of experience, such as sensation, illusion, hallucination, mental images, and what he called ‘fancy.’ We extend his approach to eleven mental categories, and discuss how these distinctions, often ignored in the empirical literature, bear on current research. We also score each category on five properties (ones abstracted from Reid) to form a 5 ×…Read more
  •  35
    The experience dependent dynamics of human consciousness
    Open Journal of Philosophy 8 (2): 116-143. 2018.
    By reviewing most of the neurobiology of consciousness, this article highlights some major reasons why a successful emulation of the dynamics of human consciousness by artificial intelligence is unlikely. The analysis provided leads to conclude that human consciousness is epigenetically determined and experience and context-dependent at the individual level. It is subject to changes in time that are essentially unpredictable. If cracking the code to human consciousness were possible, the result …Read more
  •  337
    2D geometry predicts perceived visual curvature in context-free viewing
    Computational Intelligence and Neuroscience 2015 (708759): 1-9. 2015.
    Planar geometry was exploited for the computation of symmetric visual curves in the image plane, with consistent variations in local parameters such as sagitta, chordlength, and the curves’ height-to-width ratio, an indicator of the visual area covered by the curve, also called aspect ratio. Image representations of single curves (no local image context) were presented to human observers to measure their visual sensation of curvature magnitude elicited by a given curve. Nonlinear regression anal…Read more
  •  13
    A simple working taxonomy with three classes of pictorial completion is proposed as an alternative to Pessoa et al.'s classification: area, surface, and contour completion. The classification is based on psychophysical evidence, not on the different phenomenal attributes of the stimuli, showing that pictorial completion is likely to involve mechanistic interactions in the visual system at different levels of processing. Whether the concept of “filling-in” is an appropriate metaphor for the visua…Read more
  •  134
    Color and figure-ground: From signals to qualia (edited book)
    with Adam Reeves
    Routledge. 2014.
    The laws which predict how the perceptual quality of figure-ground can be extracted from the most elementary visual signals were discovered by the Gestaltists, and form an essential part of their movement (see especially Metzger, 1930, and Wertheimer, 1923 translated and re-edited by Lothar Spillmann, 2009 and 2012, respectively). Distinguishing figure from ground is a prerequisite for perception of both form and space (the relative positions, trajectories, and distances of objects in the visual…Read more
  •  729
    Phenomena of illusory form: Can we bridge the gap between levels of explanation?
    with Lothar Spillmann
    Perception 24 1333-1364. 1995.
    The major theoretical framework relative to the perception of illusory figures is reviewed and discussed in the attempt to provide a unifying explanatory account for these phenomena
  •  19
    The biological significance of color
    with Keith Langley
    In D. Skusevich & P. Matikas (eds.), Color Perception: Physiology, Processes and Analysis, Nova Science Publishers. pp. 110--115. 2009.
    How the visual systems of different species enable them to detect and discriminate colour patterns and how such visual abilities contribute to their survival is discussed. The influence of evolutionary and environmental pressures on both perceptual capacity and colour trait production is to be considered. Visual systems with different functional anatomy have evolved in response to such pressures.
  •  22
    External regularities and adaptive signal exchanges in the brain
    Behavioral and Brain Sciences 24 (4): 663-664. 2001.
    Shepard's concept of internalization does not suggest mechanisms which help to understand how the brain adapts to changes, how representations of a steadily changing environment are updated or, in short, how brain learning continues throughout life. Neural mechanisms, as suggested by Barlow, may prove a more powerful alternative. Brain theories such as Adaptive Resonance Theory (ART) propose mechanisms to explain how representational activities may be linked in space and time. Some predictions o…Read more
  •  98
    Beyond the classic receptive field: the effect of contextual stimuli
    with Lothar Spillmann and Chia-Huei Tseng
    Journal of Vision 15 1-22. 2015.
    Following the pioneering studies of the receptive field (RF), the concept gained further significance for visual perception by the discovery of input effects from beyond the classical RF. These studies demonstrated that neuronal responses could be modulated by stimuli outside their RFs, consistent with the perception of induced brightness, color, orientation, and motion. Lesion scotomata are similarly modulated perceptually from the surround by RFs that have migrated from the interior to the out…Read more
  •  95
    Why the Brain Knows More than We Do
    Brain Sciences 2 1-21. 2011.
    Scientific studies have shown that non-conscious stimuli and représentations influence information processing during conscious experience. In the light of such evidence, questions about potential functional links between non-conscious brain representations and conscious experience arise. This article discusses models capable of explaining how statistical learning mechanisms in dedicated resonant circuits could generate specific temporal activity traces of non-conscious representations in the br…Read more
  •  308
    Light increment thresholds were measured on either side of one of the illusory contours of a white-on-black Kanizsa square and on the illusory contour itself. The data show that thresholds are elevated when measured on either side of the illusory border. These elevations diminish with increasing distance of the target spot from the white elements which induce the illusory figure. The most striking result, however, is that threshold elevations are considerably lower or even absent when the target…Read more
  •  201
    Does consciousness exist independently of present time and present time independently of consciousness
    with Jean Durup
    Open Journal of Philosophy 2 (1): 45-49. 2012.
    While some are currently debating whether time may or may not be an illusion, others keep devoting their time to the science of consciousness. Time as such may be seen as a physical or a subjective variable, and the limitations in our capacity of perceiving and analyzing temporal order and change in physical events definitely constrain our understanding of consciousness which, in return, constrains our conceptual under-standing of time. Temporal codes generated in the brain have been considered …Read more
  •  350
    Poorly saturated colors are closer to a pure grey than strongly saturated ones and, therefore, appear less “colorful”. Color saturation is effectively manipulated in the visual arts for balancing conflicting sensations and moods and for inducing the perception of relative distance in the pictorial plane. While perceptual science has proven quite clearly that the luminance contrast of any hue acts as a self-sufficient cue to relative depth in visual images, the role of color saturation in such fi…Read more
  •  250
    The Communication Contract and Its Ten Ground Clauses
    Journal of Business Ethics 87 (3): 415-436. 2008.
    Global society issues are putting increasing pressure on both small and large organizations to communicate ethically at all levels. Achieving this requires social skills beyond the choice of language or vocabulary and relies above all on individual social responsibility. Arguments from social contract philosophy and speech act theory lead to consider a communication contract that identifies the necessary individual skills for ethical communication on the basis of a limited number of explicit cla…Read more
  •  32
    We question the ecological plausibility as a general model of cognition of van der Velde's & de Kamps's combinatorial blackboard architecture, where knowledge-binding in space and time relies on the structural rules of language. Evidence against their view of the brain and an ecologically plausible, alternative model of cognition are brought forward.
  •  325
    The perceived strength of darkness enhancement in the centre of surfaces surrounded or not surrounded by illusory contours was investigated as a function of proximity of the constituent elements of the display and their angular size. Magnitude estimation was used to measure the perception of the darkness phenomenon in white-on-grey stimuli. Darkness enhancement was perceived in both types of the stimuli used, but more strongly in the presence of illusory contours. In both cases, perceived darkne…Read more
  •  659
    Interaction of color and geometric cues in depth perception: When does red mean "near"?
    with Christophe Guibal
    Psychological Research 69 30-40. 2004.
    Luminance and color are strong and self-sufficient cues to pictorial depth in visual scenes and images. The present study investigates the conditions Under which luminance or color either strengthens or overrides geometric depth cues. We investigated how luminance contrasts associated with color contrast interact with relative height in the visual field, partial occlusion, and interposition in determining the probability that a given figure is perceived as ‘‘nearer’’ than another. Latencies of ‘…Read more
  •  184
    Psychophysical measures of illusory form: Further evidence for local mechanisms
    with Claude Bonnet
    Vision Research 33 759-766. 1993.
    Detection thresholds for a small light spot were measured at various distances from the colinear inucer edges of white inducing elements on a dark background. The data show that thresholds are elevated when the target is located close to one or more inducing element(s). Threshold elevations diminish with increasing distance of the target from colinear edges and decreasing surface size of the inducing elements. gradients show the same tendencies. Tbe present observations add empirical support to …Read more
  •  57
    Double, double, toil and trouble – fire burn, and theory bubble!
    Behavioral and Brain Sciences 26 (4): 409-410. 2003.
    Lehar's Gestalt Bubble model introduces a computational approach to holistic aspects of three-dimensional scene perception. The model as such has merit because it manages to translate certain Gestalt principles of perceptual organization into formal codes or algorithms. The mistake made in this target article is to present the model within the theoretical framework of the question of consciousness. As a scientific approach to the problem of consciousness, the Gestalt Bubble fails for several rea…Read more
  •  251
    This bookreview discusses Piccolino and Wades' book on Galileo's impact on contemporary perception science
  •  44
    The heuristic value of Pylyshyn's cognitive impenetrability theory is questioned in this commentary, mainly because, as it stands, the key argument cannot be challenged empirically. Pylyshyn requires unambiguous evidence for an effect of cognitive states on early perceptual mechanisms, which is impossible to provide because we can only infer what might happen at these earlier levels of processing on the basis of evidence collected at the post-perceptual stage. Furthermore, the theory that early …Read more
  •  7
    Isoluminant color contrast does not fill in surfaces
    with C. Wehrhahn
    In Enrique Villanueva (ed.), Perception, Ridgeview. pp. 25--26. 1996.
    Results from a brightness matching procedure lead to suggest that green color Kanizsa square inducers placed on isoluminant red color backgrounds do not produce phenomenal surface enhancement.
  •  142
    A Plastic Temporal Brain Code for Conscious State Generation
    with Jean Durup
    Neural Plasticity 2009 1-15. 2009.
    Consciousness is known to be limited in processing capacity and often described in terms of a unique processing stream across a single dimension: time. In this paper, we discuss a purely temporal pattern code, functionally decoupled from spatial signals, for conscious state generation in the brain. Arguments in favour of such a code include Dehaene et al.’s long-distance reverberation postulate, Ramachandran’s remapping hypothesis, evidence for a temporal coherence index and coincidence detec…Read more
  •  138
    Visual spatial learning of complex object structures through virtual and real-world data
    with Chiara Silvestri, Rene Motro, and Bernard Maurin
    Design Studies 31 364-380. 2010.
    This article probes the visual spatial représentations underlying the creative conceptual design of complex objects.
  •  7
    The laws and principles which predict how perceptual qualities can be extracted from the most elementary visual signals were discovered by the Gestalt psychologists(e.g., Wertheimer,1923; Metzger,1930, translated and re-editedbySpillmann in 2009 and2012, respectively). Their seminal work has inspired visual science ever since, andhas led to exciting discoveries which have confirmed the Gestalt idea that the human brain would have an astonishing capacity for selecting and combining critical visua…Read more
  •  329
    Depth perception from pairs of overlapping cues in pictorial displays
    with Severine Durand and Stephen Grossberg
    Spatial Visions 15 255-276. 2002.
    The experiments reported herein probe the visual cortical mechanisms that control near–far percepts in response to two-dimensional stimuli. Figural contrast is found to be a principal factor for the emergence of percepts of near versus far in pictorial stimuli, especially when stimulus duration is brief. Pictorial factors such as interposition (Experiment 1) and partial occlusion Experiments 2 and 3) may cooperate, as generally predicted by cue combination models, or compete with contrast factor…Read more
  •  315
    Simultaneous brightness and apparent depth from true colors on grey: Chevreul revisited
    with Adam Reeves
    Seeing and Perceiving 25 (6): 597-618. 2012.
    We show that true colors as defined by Chevreul (1839) produce unsuspected simultaneous brightness induction effects on their immediate grey backgrounds when these are placed on a darker (black) general background surrounding two spatially separated configurations. Assimilation and apparent contrast may occur in one and the same stimulus display. We examined the possible link between these effects and the perceived depth of the color patterns which induce them as a function of their luminance co…Read more