Journal of Neuroscience, Vol 15, 1940-1950, Copyright © 1995 by Society for Neuroscience
The role of striate cortex in visual function of the cat
T Pasternak, J Tompkins and CR Olson
Department of Neurobiology and Anatomy, University of Rochester, New York 14627.
We examined the contribution of area 17 to visual function in two cats
whose fixation was monitored by means of scleral search coils. Ibotenic
acid lesions were made within the physiologically identified representation
of the lower left visual field of area 17. In a detection task in which the
cats simply indicated the presence or absence of a vertical grating,
contrast sensitivity loss was greatest at middle spatial frequencies with
no loss in spatial resolution. However, when cats were required to
discriminate between vertical and horizontal gratings, sensitivity loss was
profound at both middle and high spatial frequencies with an octave loss of
spatial resolution. This greater loss was not due to disrupted orientation
discrimination since sensitivity to the orientation of coarse gratings was
unaffected in the lesioned hemifield. We also found deficits in the ability
to discriminate the direction of grating motion, but only at higher spatial
and lower temporal frequencies. The role of area 17 in perceiving the
global motion of complex patterns was also studied with high contrast,
dynamic random dots drifting at high speeds. Paradoxically, area 17 lesion
improved the perception of global motion. This improvement was eliminated
by spatially filtering the dot patterns to remove high spatial frequencies,
suggesting that the lesion has enhanced performance by interfering with
masking by high spatial frequencies. Our results demonstrate that the
performance of traditional detection tasks may be insensitive to the
effects of area 17 lesions. Discrimination tasks, on the other hand,
revealed that area 17 neurons play a major role in the perception of higher
spatial frequency stimuli as long as they move or flicker at low rates, but
contribute little to these functions when the stimuli are coarse and move
at high speeds.