Saccade

Saccades are the minute lateral eye movements the eye makes that allow you to see. Since photoreceptor cells in the retina are activated by a change in the light, the eye must make these movements to keep these receptors firing and providing visual information to the primary visual cortex located in the occipital lobe of the brain.

                   thalamus    __
              ---        |     | \
           / \     \_____o_____|  \
           \ /     /           |__/
              --                    visual cortex
            eye         

Some monks who practice one point meditation have reported their vision temporarily blurring out when these movements stop.

You might imagine that when you look over a person's picture, or a live face in conversation, your eyes engage in a smooth, studied course of activity, some logical left-to-right or top-to-bottom sweep of it. But in fact, that's not how seeing things works, and what your eyes are really doing is darting around to the most visually interesting details before them, giving your brain snapshots of tiny pieces of the whole, which it quickly assembles into the idea of what you think you see. For no good reason, these are called saccades, and one way in which a human can be told from a robot has been the absence of such movement in robots. Until now, naturally, when who else but Disney has built a robot capable of producing saccades. Not, mind you, random eye movements (which would be more easily programable), but eye movements driven by an artificial intelligence which mimic the human pattern of darting to those interesting spots. So, subconsciously, you will perceive this robot, as it looks at your face, as darting its eyes back and forth to your own eyes, to your mouth, to the edges, and you will feel as if it is looking at you in an uncannily human way.

Sac*cade" (?), n. [F.] Man.

A sudden, violent check of a horse by drawing or twitching the reins on a sudden and with one pull.

© Webster 1913.