How the visual system prevents the world from fading

Abstract

Our visual system contains a built-in contradiction: when we fixate our gaze on an object of interest, our eyes are never still. Instead we produce, several times each second, small eye movements of which we are unaware, called “microsaccades”. Amazingly, if we eliminate these eye movements in the laboratory, our visual perception fades. By knowing the brain activity that occurs as result of a microsaccade, we can know the type of activity that is important for keeping objects visible. To address this, we trained macaque monkeys to fixate their eyes on a small spot and we correlated their neuronal activity with their eye movements. We learned that microsaccades increase the activity of neurons in the primary visual cortex (area V1). This increased activity tends to occur in clumps, also called “bursts”. Bursts of neuronal impulses would seem to be the type of activity most effective in sustaining a visible image.