A close-up of a computer-simulated human eye during fixation, with an inset view of the central retina. Although the eye is voluntarily “fixated” on the edge of a figure, it nevertheless makes tiny eye movements with distinct characteristics. The moving position of one point of the figure is displayed as a line on the retina in the inset. This plot reveals three types of fixational eye movements: fast microsaccades, slow drift, and oscillatory tremor, all of which move the stimulus by different amounts across the photoreceptor cells of the retina.

Eye movement animations courtesy of the Barrow Neurological Institute: Mark Schornak, Michael Hickman, Marie Clarkson, Susana Martinez-Conde, and Stephen L. Macknik