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Abstract:
When a visual image consists of a figure against a
background, V1 cells are physiologically observed to give higher
responses to image regions corresponding to the figure relative to
their responses to the background. The medial axis of the figure
also induces relatively higher responses compared to responses to
other locations in the figure (except for the boundary between the
figure and the background). Since the receptive fields of V1 cells
are very small compared with the global scale of the figure-ground
and medial axis effects, it has been suggested that these effects
may be caused by feedback from higher visual areas. I show how
these effects can be accounted for by V1 mechanisms when the size
of the figure is small or is of a certain scale. They are a
manifestation of the processes of pre-attentive segmentation which
detect and highlight the boundaries between homogeneous image
regions.
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