Spatio-temporal contingency of saccade-induced chronostasis

During fast, saccadic eye movements visual perception is suppressed. This saccadic suppression prevents erroneous and distracting motion percepts resulting from saccade induced retinal slip. Although saccadic suppression occurs over a substantial time interval around the saccade, there is no "perceptual gap" during saccades. The mechanisms underlying this temporal perceptual filling-in are unknown. When subjects are asked to perform temporal interval judgements of stimuli presented at the time of saccades, the time interval following the termination of the saccade appears longer than subsequent intervals of identical length. This illusion is known as "chronostasis", because a clock presented at the saccade target seemingly stops for a moment. We test whether chronostasis is a global mechanism that may compensate for the temporal gap associated with saccadic suppression. We show that a clock positioned halfway between the initial fixation point and the saccade target does not exhibit prolongation of the interval following the saccade. The characteristical distortion of temporal perception occurred only in the case of a clock being located at the saccade target. This result suggests a local, object-specific mechanism underlying the stopped clock illusion that might originate from a shift in attention immediately preceding the eye movement.