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Visual confidence refers to an observer's ability to judge the accuracy of her perceptual decisions. Even though confidence judgments have been recorded since the early days of psychophysics, only recently have they been recognized as essential for a deeper understanding of visual perception. The reluctance to study visual confidence may have come in part from obtaining convincing experimental evidence in favor of metacognitive abilities rather than just perceptual sensitivity. Some effort has thus been dedicated to offer different experimental paradigms to study visual confidence in humans and nonhuman animals. To understand the origins of confidence judgments, investigators have developed two competing frameworks. The approach based on signal decision theory is popular but fails to account for response times. In contrast, the approach based on accumulation of evidence models naturally includes the dynamics of perceptual decisions. These models can explain a range of results, including the apparently paradoxical dissociation between performance and confidence that is sometimes observed.

AbstractAttention Deficit/Hyperactivity Disorder (AD/HD) is often reported in gifted children. Several authors, however, suggest that gifted children, in fact display AD/HD-like behaviors, especially at school due to boredom resulting from academically understimulating environments. In order to clarify this issue, a study was conducted on 37 gifted children based on four different observational assessments of hyperactivity disorder (father, mother, teacher, child), using the Conners Rating Scale - Revised. The main results show that teachers at school observe less hyperactivity disorder than parents at home, and their perception is similar to that of the children. These fi ndings underline the importance of understanding hyperactive behavior situationally, i.e., in the context of the relational dynamics arising between a child expressing him or herself through a particular behavior and an environment that perceives this particular behavior and responds to it with different tolerance thresholds according to the observers.

Our two eyes receive different views of a visual scene, and the resulting binocular disparities enable us to reconstruct its three-dimensional layout. However, the visual environment is also rich in monocular depth cues. We examined the resulting percept when observers view a scene in which there are large conflicts between the surface slant signaled by binocular disparities and the slant signaled by monocular perspective. For a range of disparity–perspective cue conflicts, many observers experience bistability: They are able to perceive two distinct slants and to flip between the two percepts in a controlled way. We present a Bayesian model that describes the quantitative aspects of perceived slant on the basis of the likelihoods of both perspective and disparity slant information combined with prior assumptions about the shape and orientation of objects in the scene. Our Bayesian approach can be regarded as an overarching framework that allows researchers to study all cue integration aspects—including perceptual decisions—in a unified manner.

Psychophysical studies have shown that human observers resolve shapefromshading ambiguities by assuming that light is coming from aboveleft. Using eventrelated potentials ERPs, we measured the processing time of the perception of an ambiguous shaded pattern. We found that the N2 component followed the change of perceived shape with stimulus orientation.We also found that the P1 component in occipital and temporal areas was correlated with the observers' idiosyncratic bias for light source position. The precocity of the correlated ERP components suggests that the light source is represented early in the visual system. Altogether, our results indicate that shapefromshading is a mostly bottomup mechanism. NeuroReport14971–975 © 2003 Lippincott Williams & Wilkins.

Shadows provide a strong source of information about the shapes of surfaces. We analyze the local geometric structure of shadow contours on piecewise smooth surfaces. Particular attention is paid to intrinsic shadows on a surface: that is, shadows created on a surface by the surface’s own shape and placement relative to a light source. Intrinsic shadow contours provide useful information about the direction of the light source and the qualitative shape of the underlying surface. We analyze the invariants relating surface shape and light-source direction to the shapes and singularities of intrinsic shadow contours. The results suggest that intrinsic shadows can be used to directly infer illuminant tilt, qualitative global surface structure, and, at intersections with surface creases, the concavity/convexity of a surface. We show that the results obtained for point sources of light generalize in a straightforward way to extended light sources, under the assumption that light sources are convex.

Abstract:  When reaching for an object, the proximity of the object, its orientation, and shape should all be correctly estimated well before the hand arrives in contact with it. We were interested in the effects of the object’s orientation on manual prehension. Subjects were asked to reach for an object at one of several possible orientations. We found that the trajectory of the hand and its rotation and opening were significantly affected by the object’s orientation within the first half of the movement. We also detected a slight delay of the wrist relative to the forearm and a small bias of the orientation of the fingers’ tips toward the orientation of the table on which the object lay. Finally, the aperture of the hand was proportional to the physical size of the object, which shows that size constancy was achieved from the variation of the object’s orientation. Taken together, these results indicate that the three components of the movement – the transport, rotation, and opening of the hand – have access to a common visual representation of the object’s orientation.

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How do we estimate the duration of a temporal interval in a familiar context? A new study finds that it is appropriate, perhaps even advantageous, to tolerate a small bias in our estimate to reduce the overall temporal uncertainty.