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Abstract
During saccadic eye movements, the processing of visual information is transiently interrupted by a mechanism known as “saccadic suppression” [1] that is thought to ensure perceptual stability [2]. If, as proposed in the premotor theory of attention [3], covert shifts of attention rely on sub-threshold recruitment of oculomotor circuits, then saccadic suppression should also occur during covert shifts. In order to test this prediction, we designed two experiments in which participants had to orient towards a cued letter, with or without saccades. We analyzed the time course of letter identification score in an “attention” task performed without saccades, using the saccadic latencies measured in the “saccade” task as a marker of covert saccadic preparation. Visual conditions were identical in all tasks. In the “attention” task, we found a drop in perceptual performance around the predicted onset time of saccades that were never performed. Importantly, this decrease in letter identification score cannot be explained by any known mechanism aligned on cue onset such as inhibition of return, masking, or microsaccades. These results show that attentional allocation triggers the same suppression mechanisms as during saccades, which is relevant during eye movements but detrimental in the context of covert orienting.
Highlights
Visual exploration is performed mostly by moving the eyes and head in order to place the image of objects of interest onto the fovea, the most sensitive portion of the retina
In Experiment 1, we have shown that, in a dual saccadic and attentional task, the time course of perceptual performance is timelocked to the preparation and execution of the saccade, in agreement with earlier studies [16,24,25,26,27]
We extended this finding to a covert attention task, by inferring the time course of saccadic preparation from the latencies of saccades performed in an overt version of the same task
Summary
Visual exploration is performed mostly by moving the eyes and head in order to place the image of objects of interest onto the fovea, the most sensitive portion of the retina. The influential premotor theory of attention proposed, more than 30 years ago, that the implementation of attentional shifts results from the covert programming of a saccade which is not executed [3] In agreement with this view, the same brain structures have been shown to be responsible for overt and covert exploration mechanisms [5,6,7]. We are unaware of this motion because the perception of the movementinduced translation of the visual image is actively suppressed by our visual system, allowing the maintenance of perceptual stability [17]. This mechanism depends on a transient disruption of visual processing around the saccade onset [1], called ‘‘saccadic suppression’’ and is commonly thought to rely, at least partly [18], on an efference copy signal originating from oculomotor centers [2,19]
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