Journal of Neuroscience, Vol 12, 1416-1434, Copyright © 1992 by Society for Neuroscience
Periodic-pattern-selective cells in monkey visual cortex
R von der Heydt, E Peterhans and MR Dursteler
Department of Neurology, University Hospital Zurich, Switzerland.
To study the visual processing of periodic and aperiodic patterns, we have
analyzed neuronal responses in areas V1 and V2 of the visual cortex of
alert monkeys during behaviorally induced fixation of gaze. Receptive field
eccentricities ranged between 0.5 degrees and 4 degrees. We found cells
that responded vigorously to gratings, but weakly or not all to bars and
edges. In some cells the aperiodic stimuli even reduced the activity below
the spontaneous level. The distribution of a bar-grating response index
indicated a discrete population of "grating cells" characterized by more
than 10-fold superiority of gratings. We estimated that these cells have a
frequency of 4% in V1 and 1.6% in V2, and that about 4 million grafting
cells of V1 subserve the central 4 degrees of vision. The converse, cells
that responded to isolated bars but not to gratings of any periodicity, was
also observed. The grating cells of V1 were mostly (23 of 26) found in
layers 2, 3, and 4B. They preferred spatial frequencies between 2.6 and 19
cycles/degree (median, 9.3), with tuning widths at half-amplitude between
0.4 and 1.4 octaves (median, 1.0). Their tunings were narrower, and their
preferred frequencies higher, than those of other cells on average. Grating
cells were also narrowly tuned for orientation. Those of V2 were similarly
selective. The responses of grating cells depended critically on the number
of cycles of the gratings. With square waves of optimum periodicity
responses required a minimum of 2-6 grating cycles and leveled off at 4-14
(median, 7.5). The corresponding receptive field widths were 0.34-2.4
degrees (median, 0.78 degrees) for V1 and 0.72-2.4 degrees (median, 1.4
degrees) for V2. Grating cells typically gave unmodulated responses to
drifting gratings, were unselective for direction of motion, and were
strongly activated also by stationary gratings. Half of those of V1 were
monocular, the others binocular, some showing strong binocular facilitation
and disparity sensitivity. Length summation was usually monotonic, but
strong end- inhibition was also observed. In contrast to other cells,
grating cells were not activated by harmonic components. Spatial-frequency
response curves for sine-wave, square-wave, and line gratings were similar.
Square-wave gratings of one-third the preferred frequency failed to excite
the cells, while the isolated 3f component (f = the fundamental of the
square wave) of these gratings evoked strong responses. In spite of the
nonlinear features, grating cells had low contrast thresholds.(ABSTRACT
TRUNCATED AT 400 WORDS)
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