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Neurophysiological studies indicate the existence of an area in the extrastriate monkey cortex specialized for the processing of stimulus motion. The present investigation was conducted to determine whether a homologous area exits in the human cortex that underlies the processing and short-term storage of velocity information. Contrast detection and velocity discrimination thresholds were measured in a group of 23 patients with unilateral focal damage to either the lateral occipital, temporal, or posterior parietal cortex. Their results were compared to those of 23 age-matched control subjects. Detection and discrimination thresholds were determined for spatially truncated sinewave gratings presented 4 degrees eccentric of fixation randomly in either the left and right visual fields. Contrast detection thresholds were measured in a spatial two-alternative forced-choice paradigm for three different drift rates (1, 2, and 4 Hz) for leftward and rightward drift directions. Simultaneous velocity discrimination thresholds were determined for reference and test gratings presented 4 degrees left and right of fixation. Sequential velocity discrimination thresholds were measured using a delay, with a interstimulus interval (ISIs) of 1, 3, and 10 sec. In a subset of five patients with superior temporal lobe damage, spatial frequency discrimination thresholds for stationary gratings were also determined. The results indicate the following: (1) contrast detection thresholds for drifting gratings did not significantly differ between the patient and control groups; (2) velocity discrimination thresholds were significantly elevated in the patients; (3) velocity discrimination thresholds significantly increased with increasing ISI in the patients; (4) velocity discrimination thresholds were elevated most when the patients had a lesion in the superior temporal cortex; (5) in the subgroup of five patients with superior temporal lobe damage, spatial frequency discrimination thresholds were not significantly elevated. The results suggest that there is a visual area in the human posterior temporal cortex that is involved in the processing and short-term storage of the velocity of moving visual stimuli.

Visual short-term memory of stimulus velocity in patients with unilateral posterior brain damage