Comparison of the Responses to Moving Texture Patterns of Simple and
Complex Cells in the Cat's Area 17.
Casanova, C., T. Savard, J.P. Nordmann, S. Molotchnikoff, K. Minville.
Departments of Surgery-Ophthalmology and of Physiology and Biophysics,
Faculty of Medicine, University of Sherbrooke, Sherbrooke, Quebec, Canada, J1H
5N4.
APStracts 2:0131N, 1995.
SUMMARY AND CONCLUSIONS
1. Whether complex (C) cells are the only truly texture-sensitive units in the
cat's primary visual cortex remains controversial. In view of the strong
physiological significance of having putatively only one class of cells
sensitive to visual noise in the striate cortex, we reinvestigated this issue.
Sensitivities of simple (S) and C cells to noise were quantitatively studied
and compared in order to clearly document the response properties of cells in
the striate cortex to visual noise and to establish whether one can
unequivocally segregate S from C cells based on those specific properties. 2.
Receptive fields were stimulated with all relevant stimuli i.e., drifting
sine-wave gratings, electronically generated noise pattern of 256 x 256
elements (ratio 1:1 of dark and light elements), and flashing and moving bars
(both bright and dark). 3. A total of 60 S cells out of 85 (70.6%) and 90 C
cells out of 101 (81.8%) responded to the motion of visual noise. Responses of
most C cells were sustained i.e. their discharge rate was maintained at a
constant level throughout presentation of the stimulus. On the other hand,
responses of the majority of S cells were characterized by several bursts of
discharges. On average, optimal firing rates were greater for gratings than
for noise. 4. For practically all cells, responses to noise varied as a
function of direction of motion. The mean direction bandwidths were
respectively 43 +/- 24 o and 48 +/- 23 o for S and C cells. In both groups,
neurons were more broadly tuned for the direction of noise than that of
gratings (t test, p<0.001). We rarely observed bimodal tuning curves for
noise, with each peak lying on either side of the orientation curve. These
results could be expected if one considers texture stimuli not in the space
domain [as dot patterns] but in the frequency domain, i.e., patterns
containing all spatial frequencies and orientations. 5. In general, the
direction indices of S and C cells were similar whether they were stimulated
by drifting noise or gratings. S cells had a slight tendency to be more
direction selective for noise than for gratings. 6. For all S and C cells
tested, responses to noise varied as a function of drift velocity. The mean
optimal velocity was 12.9 and 10.2 o /sec for S and C cells respectively (t
test, >0.05). Most cells were bandpass with mean bandwidths of 2.2 and 2.7
octaves for S and C cells, respectively. Enlarging the size of pattern
elements yielded an increase in response amplitude and bandwidth in both cell
groups. 7. Texture-sensitive units were distributed in all layers. Strong
texture-sensitive C cells were generally located in the infragranular layers.
There was no clear relationship between laminar distribution and noise
responsiveness for S cells. 8. Our study shows that, except for response
profile and strength, there were no significant differences between response
properties of S and C cells with respect to their noise sensitivity. These
data suggest that visual noise does not allow one to clearly segregate S from
C cells. Also, they do not support the notion that C cells receive inputs not
mediated by S cells.
Received 18 August 1994; accepted in final form 17 April 1995.
APS Manuscript Number J519-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 2 May 1995.