High-acuity vision in the fovea and fine oculomotor behavior

Humans rely on the foveola, a small region approximately half the width of a thumb at arm’s length, for seeing fine spatial detail.  Outside this region, it is well established that many visual functions progressively decline with eccentricity.  Within the foveola, instead, vision is believed to be approximately uniform, however this hypothesis has never been rigorously tested, primarily because of the very presence of microscopic eye movements. In fact, mapping foveal vision is an extremely challenging task; these eye movements, which include incessant drifts and microsaccades, prevent isolation of small retinal regions. Fixational eye movements effectively homogenize measurements across adjacent retinal locations.

Eye movements during fixation.

A reconstruction of the retinal input during a period of fixation recorded
with a high-resolution eye tracker.

Using fine control of the retinal input achieved with state-of-the-art gaze-contingent technology, and high-precision eyetracking, my research has revealed that visual acuity is not uniform within the foveola and that microscopic gaze relocations are finely tuned to center visual details on the point of highest visual acuity within this small region (Poletti et al, 2013, Current Biology).

2D distribution of gaze position during fixation for one observer when performing a fine discrimination task.
White rectangles represent stimuli locations. Gaze shifts are in the order of one fourth of a degree.

Ongoing research in the lab further examines the precision, accuracy and adaptability of these microscopic gaze shifts and how these factors are linked with the distribution of visual capabilities across the foveola.