Microsaccadic eye movement generation is sufficient to enhance peripheral visual sensitivity

Microsaccades have been convincingly linked to extrafoveal covert attention shifts for more than two decades. However, the direction of causality between individual microsaccade generation and an alteration in both extrafoveal visual sensitivity and behavior remains debated: do microsaccades merely reflect, perhaps probabilistically, an altered extrafoveal sensitivity, or is the act of generating microsaccades sufficient, on its own, to modify such sensitivity? Using a novel exploitation of real-time retinal image stabilization, behavior, and neurophysiology in the superior colliculus of rhesus macaque monkeys, we show that exclusive experimental control over foveal oculomotor state is entirely sufficient to influence extrafoveal sensitivity. This happens for eccentricities as large as ~50 times those associated with microsaccades, and it also takes place in the absence of any differential attentional demands. Most importantly, such influence is mediated through well-known, classic pre- and post-saccadic visual processing changes. These results were also confirmed and extended to larger saccades, using human psychophysical experiments. Thus, seemingly-innocuous subliminal eye movements do constitute an integral component of cognitive processes like attention.