SACCADIC SUPPRESSION AND STIMULUS UNCERTAINTY

Saccadic suppression is a decline in detectability of a weak flash presented during a saccadic eye movement. We examined the hypothesis of Matin [Psychol. Bull. 81, 899 (1974)] that saccadic suppression may be due to increased stimulus uncertainty during the saccade. Uncertainty could arise from variability and inhomogeneities in the visual frame of reference translation that must accompany a saccade. We measured an average 0.6-log-unit suppression for a brief foveal 1-degrees flash in a light-adapted detection task. Receiver-operating-characteristic (ROC) slopes for flash detection during saccades, compared with those when fixating, were reduced, indicating the presence of increased uncertainty. The magnitude of this uncertainty change was estimated and found to be consistent with that required to account for the measured detectability decline. When a flashed pedestal was employed to reduce the effect of uncertainty, there was no saccadic suppression and no ROC slope change. Also, spatially separate flashed markers, intended to reduce uncertainty, led to a significant reduction in saccadic suppression for one of two subjects. Our results are consistent with the hypothesis that a saccade leaves the observer with increased uncertainty as to which subjective visual direction to attend for a stimulus of fixed retinal locus. The magnitude of this uncertainty change can account fully for the saccadic suppression measured.