Abstract
We will review evidence showing that vision is an active process even at its finest scale in the foveola. The need for an active foveola does not only originate from the fact that the visual system is primarily sensitive to changes and absence of retinal motion impairs visual perception in the fovea, but it also originates from the non-uniformity of fine spatial vision across the foveola. Using high-precision eye-tracking and a system for gaze-contingent display capable of localizing the line of sight with arcminute precision, we first demonstrate that visual crowding does not affect the whole foveola equally, as a result, under normal viewing conditions with crowded foveal stimuli, acuity drops considerably even a few arcminutes away from the preferred locus of fixation. We then illustrate the mechanisms through which active vision at this scale is achieved and its benefits. In particular, we show that ocular drift, the incessant jitter of the eye, enhances fine spatial vision to the point that acuity can be directly predicted from this oculomotor behavior. We show that microsaccades, saccades smaller than half degree, are actively used by the visuomotor system to explore the foveal stimulus and are driven by visual saliency and relevance effectively implementing strategies for visual search at this tiny scale. Finally, we discuss the interplay of attention and microsaccades in the foveola. The benefits of microsaccades also come from the ultra-fine resolution of pre-microsaccadic attention, which leads to highly localized perceptual enhancements around the goal location of microsaccades.