The Journal of Neurophysiology Vol. 83 No. 4 April 2000, pp. 1900-1911
Copyright ©2000 by the American Physiological Society
Integration of Foveal Orientation Signals: Distinct Local and
Long-Range Spatial Domains
Scott L.
Brincat and
Gerald
Westheimer
Division of Neurobiology, University of California, Berkeley,
California 94720
Brincat, Scott L. and
Gerald Westheimer.
Integration of Foveal Orientation Signals: Distinct Local and
Long-Range Spatial Domains. J. Neurophysiol. 83: 1900-1911, 2000. Human observers can discriminate
the orientation of a stimulus configuration composed of a pair of
collinear visual patterns much better than that of a single component
pattern alone. Previous investigations of this type of orientation
signal integration and of other similar visual integrative functions
have shown that, for closely spaced elements, there is integration only
for stimuli with the same contrast polarity (i.e., both lighter or both
darker than the background) but, at greater separations, integration is
independent of contrast polarity. Is this effect specific to differences in contrast polarity, which is known to be an important parameter in the organization of the visual system, or might there be a
cluster of other stimulus dimensions that show similar effects, indicating a more widespread distinction between the processes limiting
integration at local and long-range spatial scales? Here, we report a
similar distance dependence for orientation signal integration across
stimulus differences in binocular disparity, direction of motion, and
direction of figure-ground assignment. We also demonstrate that the
selectivity found at short separations cannot be explained only by
"end-cuts," the small borders created at the junction of abutting
contrasting patterns. These findings imply the existence of two
distinct spatial domains for the integration of foveal orientation
information: a local zone in which integration is highly selective for
a number of salient stimulus parameters and a long-range domain in
which integration is relatively unselective and only requires that
patterns be roughly collinear.
