Electrophysiological and Psychophysical Studies of the Effects of the Duration of Presentation of Textures on Recognition Thresholds

The relationships between the number of correct responses, reaction time, and the main characteristics of visual evoked potentials (VEP) on the one hand, and the duration of stimulus presentation on the other were studied in tasks based on recognition of the dominant orientation of textures with different levels of ordering. Stimuli were presented for 30, 60, 130, 250, 500, and 1000 msec. The duration of presentation at which all subjects coped with the task was no greater than 130 msec in our experiments, and this coincided with the duration of stimulus presentation at which differences in EP depending on recognition task difficulty were seen. The first significant changes in EP depending on task difficulty developed 300 msec after the beginning of stimulus presentation and consisted of increases in the amplitude of the P300 component in response to the matrixes which were easiest to recognize. The coincidence of the recognition time thresholds and the appearance of differences in EP suggest that individual VEP waves may reflect activity associated with image recognition processes. The time characteristics of these processes were found to differ in different subjects. Two groups of observations were identified, with different time characteristics for perception and EP development.