Summary

I have sought to describe the many functional properties of oculomotor systems and also to show that among them, several contribute to the spatial qualities of experience: convergence and accommodation signal distance in near space (Fisher & Ciuffreda, 1988; Mon-Williams & Tresilian, 1999), and also modulate the sense of depth and size (van Damme & Brenner, 1997); saccades and the fixation reflex they subserve signal the direction of a target from the egocenter (Matin & Pearce, 1965; Lewald & Ehrenstein, 2000). Not quite so obvious is the fact that this directional information also controls other perceptual qualities such as apparent slant and inclination of surfaces as well (Ebenholtz & Paap, 1973, 1976; Backus, Banks, van Ee, & Crowell, 1999).

On the dynamic side, evidence has shown that the slow pursuit system imparts the quality of motion and length of movement path to fixated objects (Mack & Herman, 1972; Honda, 1990) regardless of whether they actually are in movement: when engendered as compensation for optokinetic nystagmus (OKN) or the vestibulo-ocular reflex (VOR), the pursuit system imbues a fixated and stationary object with illusory movement (Mach, 1906/1959; Post & Leibowitz, 1985). Also to be noted is that, from a methodologic perspective, studies have been emphasized that have demonstrated changes in space perception as a result of modulation of the control parameters or the states of various oculomotor systems (e.g., Gauthier & Robinson, 1975; Ebenholtz & Fisher, 1982; Mon-Williams & Tresilian, 1999).

Implications

What are the implications of failing to recognize the perceptual contributions of oculomotor systems? The foremost and simplest answer is that it would lead to incomplete knowledge of our visual and perceptual systems.