Areas V3 and V4 are commonly thought of as individual entities in the primate
visual system, based on definition criteria such as their representation of
visual space, connectivity, functional response properties, and relative
anatomical location in cortex. Yet, large-scale functional and anatomical
organization patterns not only emphasize distinctions within each area, but also
links across visual cortex. Specifically, the visuotopic organization of V3 and
V4 appears to be part of a larger, supra-areal organization, clustering these
areas with early visual areas V1 and V2. In addition, connectivity patterns
across visual cortex appear to vary within these areas as a function of their
supra-areal eccentricity organization. This complicates the traditional view of
these regions as individual functional “areas.” Here, we
will review the criteria for defining areas V3 and V4 and will discuss
functional and anatomical studies in humans and monkeys that emphasize the
integration of individual visual areas into broad, supra-areal clusters that
work in concert for a common computational goal. Specifically, we propose that
the visuotopic organization of V3 and V4, which provides the criteria for
differentiating these areas, also unifies these areas into the supra-areal
organization of early visual cortex. We propose that V3 and V4 play a critical
role in this supra-areal organization by filtering information about the visual
environment along parallel pathways across higher-order cortex.