The mapping of visual space is a function of the structure of the visual field

Flanders et al.'s model predicts that subjects use a shouldercentered reference system to determine the position of remembered targets for reaching. Other studies of goal-directed arm movements have found other areas in the bodv architecture to be the center of the coordinate system (e.g.: head-centered: Bard et al. 1990; Biguer et al. 1982; trunk-centered: Yardley 1990). Common to these studies is the suggestion that an egocentric (or bodycentered) reference system is used to process spatial information. Discrepancies among these models arise from the identification of the coordinate system's origin. A body-centered mapping refers to a sensorimotor mode of processing spatial information characterized by a direct dialogue with the physical world by continuously updating proprioceptive information with the registration of gaze direction (Paillard 1986). In addition to bodycentered coordinate systems, there is experimental evidence for the existence of an allocentric frame of reference capable of cognitively processing spatial information and thus determining the position of an object in space (Bridgeman et al. 1979; 1989; Paillard et al. 1981; 1991). This allocentric system derives from a memory-based internal construct built from extracting the stable covariant features of a structured visual environment. It corresponds to the representational (Paillard 1986) or the cognitive (Bridgeman 1989) mode of processing spatial information.