Abstract: Perception-action double-system theory of vision argues that the ventral and dorsal streams are distinct systems whose functions are, separately, representing the world and directing the action, which associates with dissociation in their processing. Views on the relation between the two pathways fall into two classes: traditional views that deny such a perception-action division, and cooperative views that emphasize interaction between the two systems. This article summarizes the key issues, empirical evidences, and contributions of each theory/view, and analyzes the conditions that visual processing takes place in a certain system, then concludes that the relative function division between the two systems leads to variety in visual processing.

Key words: vision, visually-directed action, ventral pathway, dorsal pathway.