Introduction

In this chapter, the wide variety of eye movement systems is described and their functions analyzed. For discussion are such issues as:

The functional significance of moving eyes.

What enables the eye to focus.

Where the eyes converge and focus when in complete darkness.

Seeing single with two eyes.

Why some eye movements are rapid and jerky, whereas others are slow and smooth.

Eye movements that respond to linear and angular acceleration of the head.

The natural intelligence of eye-movement control systems.

Oculomotor systems in space.

Types of Eye Movements

Eye movements come with a wide variety of characteristics and seem to have evolved to provide rather specific functions. For example, saccades, which are flicks of the eyeball also known as rapid eye movements (REMs) when occurring during sleep, move a peripheral retinal image rapidly onto the fovea. Saccades occur when reading or whenever inspecting objects of interest (Stark & Ellis, 1981) and can be over in just a few milliseconds. Therefore, Saccades function to minimize the amount of time the eye is in flight, when retinal images may be subject to intense smear. Pursuit movements, however, permit the eye to move with the same velocity as the retinal image so that a moving target may be tracked and surveilled continuously. This holds for eye velocities as high as 100 degs sec−1 (Meyer, Lasher, & Robinson, 1985), but saccades can be up to ten times as fast.