Journal of Neuroscience, Vol 7, 482-500, Copyright © 1987 by Society for Neuroscience
Spatial and temporal selectivity in the suprasylvian visual cortex of the cat
TJ Zumbroich and C Blakemore
We recorded from single units in the medial and lateral banks of the
posterolateral suprasylvian visual cortex (PMLS/PLLS) of the cat. The
responses to drifting high-contrast gratings of optimum orientation and
direction of motion, but varying in spatial and temporal frequency, were
examined quantitatively for a sample of cells, whose receptive fields
covered a wide range of eccentricities. The optimum spatial frequencies
(average about 0.2 cycles/deg) were low compared to the values reported for
striate cortex but similar to those for area 18. The mean spatial bandwidth
(about 2 octaves) was slightly broader than that of cells in other cortical
visual areas. The cut-off spatial frequencies ("acuities") covered a wide
range, from 0.05 to 2.1 cycles/deg, similar to those of cells in area 18.
Responses to drifting sinusoidal gratings were usually dominated by an
unmodulated elevation of discharge, although some modulation occurred at
the temporal frequency of drift, especially at low spatial frequencies.
Modulated responses were relatively stronger in PMLS than in PLLS. For
those cells that responded to flashed stimuli, stationary,
contrast-modulated gratings presented at different spatial positions
typically evoked small responses at the fundamental frequency (dependent on
spatial phase) and a larger component at the second harmonic of temporal
frequency, with no overall "null-position." The optimum spatial frequency
was usually higher than would be predicted by simple summation within the
dimensions of the receptive field. Thus, neurons in PMLS and PLLS, like
complex cells in areas 17 and 18, behave nonlinearly and their spatial
selectivity is determined by "subunits" smaller than their receptive
fields. The range of preferred temporal frequencies ranged from less than
2.5 Hz to more than 10 Hz. In their temporal selectivity neurons in PMLS
resembled cells in area 17, with little attenuation at low temporal
frequencies, whereas there was a tendency for cells in PLLS to prefer
higher temporal frequencies, as is common in area 18.