TRANSIENT MOTION OF VISUAL TEXTURE DELAYS SACCADIC EYE-MOVEMENTS

Neurophysiological research has established that a transient stimulus, spatially located outside the receptive field of visual cells, can ac tivate some cells and inhibit firing in others. However, the significa nce of this phenomenon for behavioural responses in man is unclear. Th is study investigated the effect of a transient peripheral event on th e initiation of saccadic eye movements to a luminance increment. In Ex periment 1 human saccadic eye movements to targets that varied in lumi nance were compared on 'shift' trials, in which the saccadic target wa s timed to coincide with a step displacement of a vertical grating in the background, and on 'no-shift' trials, when the background remained stationary. The results showed a significant delay in mean saccadic l atencies on 'shift trials' compared to 'no-shift' trials. Saccadic lat encies were reduced in both conditions with increasing target intensit y. Measurement of visual sensitivity showed a small non-significant in crease in thresholds in the background 'shift' condition. A second exp eriment manipulated visuo-temporal information by varying both target duration and intensity. This experiment revealed significant effects o f target duration and signal intensity on saccadic latency; and a 3-wa y interaction showing that saccades suffered the greatest delay in the background 'shift' condition at the lowest duration and intensity tar gets. These results show that the peripheral motion of visual texture delays the programming of saccadic eye movements and there is a partic ularly marked effect for targets of low signal strength.