Role and mode of action of the extraretinal factors documenting the orientation of the eyes in the orbit, in the localization of the objects in space

Abstract

The role of the extraretinal factors in the programmation of goal-directed arm movements and in the elaboration of an internal representation of the visual space was investigated. The experimental method used for understanding these mechanisms is the analysis of the final precision of visually guided arm movements. The results of the author's study suggest that (1) the target location is internally represented in a body-centred reference system, (2) this information is used to control the final arm position and (3) orienting the eyes towards the target changes the egocentric axis of reference used for building the internal representation of the body midline (eyes axis replaced by head-trunk axis). This hierarchical organization could be explained by the necessity of a stable body-related reference point in order to ensure a stable visual perception of the surrounding space, despite moving one of the egocentric axes with respect to the others.

Key Words:

• extraretinal factors
• space orientation