A COMPARATIVE-ANALYSIS OF SPATIAL MEMORY PROCESSES

This paper reviews spatial memory processes in three highly evolved ta xa: hymenoptera, birds and mammals. In these three taxa, the goal loca tion can be memorized egocentrically as a vector specifying the head-r eferred direction and the distance to the goal, and/or exocentrically as a view specifying the spatial layout of the surrounding landmarks p erceived by the animal when standing at the goal. The egocentric codin g process requires a path-integration mechanism to update the memorize d goal location as a function of the animal's current position. Change s of direction are estimated allothetically (by reference to an extern al compass) in hymenoptera, idiothetically (on the basis of internal m ovement-related information) in mammals, and probably in both ways in birds. Computer simulations have shown that path-integration is very s ensitive to random errors occurring in idiothetic but not in allotheti c estimations. When using the exocentric coding process, hymenoptera s tore the bearings and angular sizes of landmarks in a compass-oriented colour snapshot taken at the goal. They ay then return to the goal by moving so as to reduce the discrepancy between the current view of la ndmarks and the memorized snapshot. In mammals, this process can be ac counted for by a neurobiologically plausible model which highlights th e fundamental role of exploration of the environment. The way this pro cess is implemented in birds is less clear.