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Neural responses that keep the world from fading

Susana Martinez-Conde

Harvard University

When retinal images are stabilized the visual world fades from perception. When we voluntarily fixate our gaze, however, the world does not fade. The reason is that during fixation we produce tiny eye movements of which we are unaware. These eye movements, called microsaccades, refresh the retinal image several times a second, thus preventing adaptation and visual fading. Neural activity correlated with microsaccades may then be important to convey the visibility of a stimulus. To determine the nature of this neural activity, we trained macaque monkeys to fixate their gaze on a small spot while recording from cells in the early visual system. We presented bars of light to the receptive fields of the cells we recorded from. We then correlated the occurrence of microsaccades during fixation with neural activity. We found that microsaccades are best correlated with bursts of spikes in the LGN and area V-1. This suggests that bursts of spikes may best represent the visibility of a stimulus to higher visual areas.