Contrast gain measurements and the transient/sustained.
We measure threshold for a vertical test grating superimposed on a fixed-contrast horizontal background grating of the same spatial and temporal frequency. The rate of change of this threshold with increasing contrast of the background grating is a measure of the contrast gain of the responding mechanism. Large slopes (high contrast gains) occur when spatial frequency is low and temporal frequency is high; small slopes (low contrast gains) occur when both spatial and temporal frequencies are low and when spatial frequency is high. This division of the spatiotemporal frequency domain into low- and high-gain regions is consistent with the transient/sustained dichotomy found in previous psychophysical studies. Furthermore, our results suggest that the mechanism responsible for detecting low spatial frequencies has a gain characteristic similar to that of cat retina Y cells and that the mechanism responsible for detecting high spatial frequencies has a gain characteristic similar to that of cat retina X cells, as found by Shapley and Victor [J. Physiol. (London) 285, 275-298 (1978)].
D006801:Humans; D008905:Minicomputers; D010364:Pattern Recognition, Visual / Q000502:physiology; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology*; D014785:Vision, Ocular / Q000502:physiology*