Abstract
How the visual system achieves perceptual stability across saccadic eye movements is a long-standing question in neuroscience. It has been proposed that an efference copy informs vision about upcoming saccades, and this might lead to shifting spatial coordinates and suppressing image motion. Here we ask whether these two aspects of visual stability are interdependent or may be dissociated under special conditions. We study a memory-guided double-step saccade task, where two saccades are executed in quick succession. Previous studies have led to the hypothesis that in this paradigm the two saccades are planned in parallel, with a single efference copy signal generated at the start of the double-step sequence, i.e. before the first saccade. In line with this hypothesis, we find that visual stability is impaired during the second saccade, which is consistent with (accurate) efference copy information being unavailable during the second saccade. However, we find that saccadic suppression is normal during the second saccade. Thus, the second saccade of a double-step sequence instantiates a dissociation between visual stability and saccadic suppression: stability is impaired even though suppression is strong.
Highlights
How the visual system achieves perceptual stability across saccadic eye movements is a long-standing question in neuroscience
The visual scene sweeps across the retina with high-speed motion
The first problem has been connected with the neurophysiological finding of receptive field remapping: neurons in parietal[1], frontal[2,3] and even in early visual areas[4,5] shift their receptive field before the saccade, to that location the receptive field will cover after the saccade, effectively counteracting the spatial displacement of the retinal image
Summary
How the visual system achieves perceptual stability across saccadic eye movements is a long-standing question in neuroscience. Previous studies have led to the hypothesis that in this paradigm the two saccades are planned in parallel, with a single efference copy signal generated at the start of the double-step sequence, i.e. before the first saccade. There is the high-speed motion of the eye itself, which produces retinal smear, making the fine details in our visual scene effectively invisible. Not all stimuli are invisible during saccades – motion that is too fast to be resolve may become visible only during the saccade, if the movement of the retina counteracts and effectively slows down the motion of the stimulus[13,14] Another passive factor is masking: the blurred intra-saccadic image can be masked by high contrast images acquired before and after the saccade[15]. Much research has attempted to identify the neural underpinnings of such mechanism, these are still unclear[25,26,27]
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