Abstract not found

Abstract not found

Contour integration in low-level vision is believed to occur based on lateral interaction between neurons with similar orientation tuning. How such interactions could arise in the brain has been an open question. Our model suggests that the interactions can be learned through input-driven self-organization, i.e. through the same mechanism that underlies many other developmental and functional phenomena in the visual cortex. The model also shows how synchronized firing mediated by these lateral connections can represent the percept of a contour, resulting in performance similar to that of human contour integration. The model further demonstrates that contour integration performance can differ in different parts of the visual field, depending on what kinds of input distributions they receive during development. The model thus grounds an important perceptual phenomenon onto detailed neural mechanisms, so that various structural and functional properties can be measured, and predictions can be made to guide future experiments. 1

It is an exciting time to study visual object perception. Although object perception research has a long tradition, lately its visibility in cognitive science and neuroscience has greatly increased. One reason for heightened interest is that diverse areas of research now suggest a central role for objects in many aspects of human cognition, including the

Contour integration in low-level vision is believed to occur based on lateral interaction between neurons with similar orientation tuning. The exact neural mechanisms underlying such interactions, and their developmental origins, are not well understood. This paper suggests through computational simulations that synchronized firing of neurons mediated by patchy lateral connections, formed through input-driven selforganization, can serve as such a mechanism. Furthermore, we argue that different degree of such patchy connections established during development may explain why different areas of the visual field show different degrees of contour integration in psychophysical experiments. Introduction Contour integration in low-level vision means forming a single coherent percept (i.e. a continuous contour) from a discontinuous sequence of line segments. Humans are very good at contour integration; understanding the underlying mechanisms can give us insights into how perceptual...

Previous studies have suggested that the integration of orientation information across space is impaired in amblyopia. We developed a method for quantifying orientation-domain processing using a test format that is suitable for clinical application. The test comprises a graded series of cards where each card includes a closed path (contour) of high contrast Gabor signals embedded in a random background of Gabor signals. Contour visibility in both normals and patients with histories of abnormal binocular vision depends jointly on the spacing of elements on the contour as well as background element density. Strabismic amblyopes show significant degradation of performance compared to normals. Small but significant losses in sensitivity were also observed in a group of non-amblyopic strabismus patients. Threshold measurements made with contrast reducing diffusers indicated that the amblyopic loss is not due to the reduced contrast sensitivity of the amblyopic eye. An abnormal pattern of long-range connectivity between spatial filters or a loss of such connectivity appears to be the primary source of contour integration deficits in amblyopia and strabismus. 2000 Elsevier Science Ltd. All rights reserved.