A close-up of a computer-simulated human eye during fixation, with an inset view of the visual scene. 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 the very center of the retina is displayed as a line on the figure in the inset. This plot reveals three types of fixational eye movements: fast microsaccades, slow drift, and oscillatory tremor.

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