Fast Perceptual Learning in Orientation Discrimination: An ERP Study

Abstract:
Abstract: Several studies have established that perceptual learning on simple visual stimuli can be observed after a very short phase of training. Because this learning does not transfer to slightly modified stimuli, it is usually regarded as evidence that early levels of visual processing are influenced. The aim of the present study was to investigate the time course of this rapid visual learning in orientation discrimination. Four blocks (48trials) of gratings distributed around a given oblique orientation were presented ; learning transfer was assessed by presenting four blocks of gratings in the orthogonal orientation. Subjects had to discriminate delayed pairs of gratings that differed by 4°. Thirteen out of 20 subjects showed a significant improvement in their performance (71% of correct responses to 91%) during the first 4 blocks; the remaining subjects performed at ceiling from the 1st bloc. Nevertheless both groups showed an abrupt decrement of performance when transfer to the orthogonal orientation was assessed. Recordings of evoked potentials revealed that modulations (smaller latencies and larger amplitudes) of early visual P1 component occurred solely in subjects who improved their performance; the later visual N1 component was altered for all subjects. These results suggest that fast learning in orientation discrimination takes place at an early stage of visual information processing.