Barthélemy F, Castet E, Masson G S, 2003, "Contrast response function and spatial summation area of human short-latency ocular following" Perception 32 ECVP Abstract Supplement
Contrast response function and spatial summation area of human short-latency ocular following
F Barthélemy, E Castet, G S Masson
Short-latency ocular following responses in humans involve spatial integration of motion signals across the visual field. We investigated the contrast response function and the spatial summation area of these responses, for both grating and pattern motion. Movements of the right eye were recorded by the scleral search coil technique (three subjects: two authors, one naïve). Vertical moving gratings (0.27 cycle deg-1, 10 Hz) or unikinetic plaids (the sum of a vertical, moving grating, and an oblique, static grating of same SF) were briefly presented (200 ms) on a large (70 deg × 70 deg) projection screen, within a circular window (diameter: 2.5 - 20 deg). Luminance of the display was carefully calibrated. Mean background luminance was of 12.5 cd m-2. The total contrast of gratings and plaids was varied from 2.5% to 80%. Increasing the contrast of a moving grating reduced the latency and increased the amplitude of the earliest tracking responses. Contrast response functions showed a steep increase (half saturation, ~ 10%) followed by a plateau. Increasing the size of the stimulus induced a strong increase in the response amplitude for radius up to ~ 10 deg, followed by a plateau. Spatial summation functions were independent from contrast. Unikinetic plaids elicited an early (~85 ms) component in the grating motion direction and a late (~ 110 ms) component in the pattern motion direction. These components showed different half-saturation contrast values of ~ 10% and ~ 20%, respectively. These results unveil the spatial properties of a 'functional receptive field' for the initiation of tracking eye movements.
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