PERCEPTUAL DISCRIMINATION IN MONKEYS - RETROACTIVE VISUAL MASKING

Five monkeys were trained to discriminate between a square and a triangle presented in a 5 msec tachistoscopic flash with 95-100 per cent accuracy. An essential feature of this trained performance was a programmed sequence of events in which the monkey learned to attend following self-triggering of the stimulus flash. When the monkeys had learned to make the perceptual discrimination with nearly 100 per cent accuracy, the test flash (T) presenting the patterns was followed by a nonpatterned blanking flash (B) at various interstimulus intervals (ISI). When the ISI was 40 msec or greater B had no effect on the perceptual discrimination of T and correct performance of the task remained at 95-100 per cent as in the case of T presented alone. At ISIs of 30-40 msec performance level decreased, suggesting partial masking of T by B; at ISIs of 15-25 msec performance in the visual discrimination task fell to a chance level indicating complete retroactive or backward masking of T by B. These results are in accord with human perceptual blanking or masking studies and have opened the way to investigation of the locus of visual masking by electrophysiological recording in the visual system of monkeys. © 1969.