DELAYED PATTERN-DISCRIMINATION IN PATIENTS WITH UNILATERAL TEMPORAL-LOBE DAMAGE

Behavioral and neurophysiological studies in macaque monkeys suggest a role of the inferior temporal cortex in pattern discrimination and vi sual memory. To determine whether this cortical area is also involved in human short-term visual memory, we measured spatial frequency discr imination thresholds for sequentially presented stimuli in 17 patients with unilateral, postoperative focal damage to the temporal cortex (1 1 left, 6 right hemisphere). These results are compared to those of 17 age-matched control subjects. Contrast detection thresholds and diffe rence thresholds for spatial frequency were determined for spatially t runcated sine wave gratings presented in the left and right visual fie lds. Detection thresholds were measured for sine wave gratings in a sp atial two-alternative forced-choice procedure for three spatial freque ncies [2.5, 5, and 10 cycles (c)/degree] for each hemifield. Discrimin ation thresholds were determined for two gratings sequentially present ed either 4-degrees to the left or right of fixation. Grating contrast was five times the value of detection threshold and reference frequen cy was 5 c/degree. Within each trial, the gratings were separated in t ime by 1, 3, and 10 sec interstimulus intervals (ISIs), and subjects s ignaled which grating had the higher spatial frequency. The results in dicate that (1) contrast detection thresholds overall did not differ b etween patient and control groups; (2) spatial frequency discriminatio n thresholds were, however, significantly elevated in patients and thi s elevation was significantly more pronounced in the visual field cont ralateral to the damaged hemisphere; and (3) patients with inferotempo ral damage exhibited higher discrimination thresholds for the longest ISI, whereas patients with medial/superior temporal lobe damage did no t show this effect. The results suggest that visual areas in human tem poral cortex are involved in the higher visual processes underlying de layed pattern discrimination.