SPATIAL MEMORY IN LARGE-SCALE MOVEMENTS - EFFICIENCY AND LIMITATION OF THE EGOCENTRIC CODING PROCESS

The orientation abilities exhibited by many species are based on spatial memorization. The location of a place to which an animal intends to return may be memorized either independently of the animal's position (location and orientation) by an exocentric coding which consists of processing the location-based (site-dependent) information provided by nearby landmarks perceptible both from the animal's location and the place, or in relation to the animal's position by an egocentric coding which consists of processing the route-based (site-independent) information provided by the animal's movements (rotations and translations). An animal seldom has the opportunity of processing useful location-based information during large scale movements in its home range, except during the terminal adjustment of its path. Consequently, it may memorize the directions and the distances of the preferential places in its home range by processing route-based information. The efficiency of this egocentric coding process was quantified as a function of the path characteristics and the type and magnitude of route-based information estimation errors. This process was found to require a high degree of accuracy in idiothetic (internal) estimations of rotatory movements but not in estimations of translatory movements or in allothetic (compass-based) estimations of rotatory movements. The complementarity of the exocentric and egocentric coding processes during large scale movements is discussed. © 1990 Academic Press Limited All rights reserved.