VISUAL-DISCRIMINATION AND SHORT-TERM-MEMORY FOR RANDOM PATTERNS IN PATIENTS WITH A FOCAL CORTICAL LESION

Visual discrimination and short-term recognition memory for computer-g enerated random patterns were explored in 23 patients with a postsurgi cal lesion in one of the cortical hemispheres. Their results are compa red with those of 23 age-matched volunteers. In a same-different force d-choice discrimination task, d' and log beta (measures of sensitivity and bias), as well as reaction time (RT) were determined. All partici pants viewed patterns defined either by luminance contrast or isolumin ant red-green color contrast, the amplitude of which was adjusted to b e 10 times the respective detection threshold level. Block patterns co nsisting of a 6 x 6 matrix of light and dark (red and green) checks we re randomly configured on each presentation. They were presented in pa irs, randomly in two visual quadrants for a duration of 200 msec. Thre e presentation conditions were used: simultaneous presentation of refe rence and test stimulus, sequential presentation with a short delay (i nterstimulus interval, ISI = 3 s), and sequential presentation with a long delay (ISI = 6 s). The results indicate that patients with a lesi on in the occipitotemporal cortex, the superior temporal cortex and th e frontal cortex were significantly impaired on both luminance contras t and color-contrast pattern discrimination. Patients with damage in t he anterior inferotemporal cortex showed no overall impairment. The re sults suggest that performance in visual discrimination and recognitio n memory tasks rely on distributed neural processes with more than one neocortical location.