Introduction

Just how perceptions get to be triggered along with certain motor acts will eventually be answered when the underlying neural networks are better understood. For now, it is clear that although certain oculomotor systems such as convergence and pursuit are associated with conscious states, others such as the VOR and OKN are not. Furthermore, the circumstances under which these systems become active frequently are indirect and not at all apparent. The compensation theories discussed in this chapter provide good examples of how one oculomotor system comes to be turned off or suppressed while another is substituted with frequently surprising perceptual results. Likewise, compensating for the effects of oculomotor adaptations although not requiring substitution of one system for another requires voluntary internal changes in innervation level or directional control. In this way, they also provide the occasion for surprising perceptual outcomes.

In addition to compensating activity, other modulating factors play a role in determining the magnitude of perceptual effects associated with oculomotor systems. Some of these discussed here are ambient light levels, voluntary and reflexive oculomotor activity, and transient vs. steady-state eye movements. Additional topics include the role of eye movements in motion sickness and the remarkable phenomenon of induced self-movement (vection).

Compensation Theories: Role of Reflexive and Voluntary Eye Movements in Normative Perception and Illusions

Early in the development of the modern period of vision sciences, eye movement effort was recognized as a significant factor in controlling egocentric location and apparent movement.