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-generated random patterns were explored in 23 patients with a postsurgicallesion in one of the cortical hemispheres. Their results are compared withthose of 23 age-matched volunteers. In a same- different forced-choicediscrimination task, d' and log beta (measures of sensitivity and bias), aswell as reaction time (RT) were determined. All participants viewedpatterns defined either by luminance contrast or isoluminant red-greencolor contrast, the amplitude of which was adjusted to be 10 times therespective detection threshold level. Block patterns consisting of a 6 x 6matrix of light and dark (red and green) checks were randomly configured oneach presentation. They were presented in pairs, randomly in two visualquadrants for a duration of 200 msec. Three presentation conditions wereused: simultaneous presentation of reference and test stimulus, sequentialpresentation with a short delay (interstimulus interval, ISI = 3 s), andsequential presentation with a long delay (ISI = 6 s). The results indicatethat patients with a lesion in the occipitotemporal cortex, the superiortemporal cortex and the frontal cortex were significantly impaired on bothluminance-contrast and color-contrast pattern discrimination. Patients withdamage in the anterior inferotemporal cortex showed no overall impairment.The results suggest that performance in visual discrimination andrecognition memory tasks rely on distributed neural processes with morethan one neocortical location.