Interference during eye movement preparation shifts the timing of perisaccadic compression.

Abstract

Our perception of the surrounding environment remains stable despite the fact that we frequently change the retinal position of input by rapid gaze shifts (saccades). There is a long-standing debate whether visual stability depends on an active mechanism using an efference copy of the impending saccadic motor command. Behavioral studies showing changes in perception around the time of saccades are consistent with a predictive mechanism, but previous studies of perceptual effects in humans confounded saccade programming with the resulting physical eye movement. In three experiments, we used a saccadic inhibition (SI) paradigm to delay saccadic onset while participants were performing a perisaccadic localization task. As expected, the perceived position of the probe stimulus was systematically biased (compressed) toward the saccadic goal, already during the presaccadic interval. In the SI condition, the localization error was shifted in time, in line with it following saccade intention rather than execution. The pattern was not the consequence of the probe being captured by the timing of the flashed distractor, but depended instead on the delay in saccadic onset time caused by SI. Importantly, the same configurations of perceptual probes presented with a flashed backward mask when participants maintained fixation did not lead to similar localization errors as saccade trials. This pattern of results is consistent with an active, sensorimotor explanation for perisaccadic mislocalization and, more generally, theories emphasizing the role of motor prediction in visual stability.