Abstract
When visual stimuli are presented at the onset of a saccadic eye movement they are seen compressed onto the target location of the saccade. This peri-saccadic compression is believed to result from internal feedback pathways between oculomotor and visual areas of the brain. This feedback enhances vision around the saccade target at the expense of localization ability in other regions of the visual field. Although saccades can be targeted at only one object at a time, often multiple potential targets are available in a visual scene, and the oculomotor system has to choose which target to look at. If two targets are available, preparatory activity builds-up at both target locations in oculomotor maps. Here we show that, in this situation, two foci of compression develop, independent of which of the two targets is eventually chosen for the saccade. Our results suggest that theories that use oculomotor feedback as efference copy signals for upcoming eye movements should take the possibility into account that multiple feedback signals from potential targets may occur in parallel before the execution of a saccade.
Highlights
Saccadic gaze shifts during the viewing of a scene result from a complex interplay between target selection, allocation of attention, movement planning, and movement initiation
In the double target condition, saccade landing positions were distributed between the two target locations with a bias toward the upper location which was consistently chosen more often than the lower target location in three of the four subjects
Our results show that the focus point of peri-saccadic compression does not depend on the executed saccade
Summary
Saccadic gaze shifts during the viewing of a scene result from a complex interplay between target selection, allocation of attention, movement planning, and movement initiation. Even when only a single target is present, as in many typical experiments on saccades, a number of processes have to be completed in the latency period before saccade initiation: The target is sensed and represented in visuomotor areas, attention is allocated to the target location (Kowler et al, 1995; Deubel and Schneider, 1996; Bisley and Goldberg, 2003), preparatory activity begins to build-up in motor regions (Glimcher and Sparks, 1992; Munoz and Wurtz, 1995; Hanes and Schall, 1996), fixation is released (Fischer and Boch, 1983; Dorris and Munoz, 1995), and the saccade is initiated by a burst of activity of motor neurons (Bruce and Goldberg, 1985; Munoz and Wurtz, 1995; Hanes and Schall, 1996) The bulk of these activities takes place within the last 50 ms or so before saccade initiation. These phenomena are often related to the insurance of perceptual continuity across the saccade, and are believed to involve an efference copy signal or corollary discharge of the saccade command
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