Spatial memory: how egocentric and allocentric combine

Recent experiments indicate the need for revision of a model of spatial memory consisting of viewpoint-specific representations, egocentric spatial updating and a geometric module for reorientation. Instead, it appears that both egocentric and allocentric representations exist in parallel, and combine to support behavior according to the task. Current research indicates complementary roles for these representations, with increasing dependence on allocentric representations with the amount of movement between presentation and retrieval, the number of objects remembered, and the size, familiarity and intrinsic structure of the environment. Identifying the neuronal mechanisms and functional roles of each type of representation, and of their interactions, promises to provide a framework for investigation of the organization of human memory more generally.

Introduction

The nature of the representations underlying human spatial cognition has long been the subject of intense debate [1]. Four years ago, an influential opinion piece [2] suggested that spatial memory was solely supported by ‘egocentric’ representations of location (i.e. centered on parts of the body), together with a representation of the surface geometry of the environment that enables the reorientation of a disoriented individual. This simple model inspired several experiments in cognitive psychology. Here, I review some of these recent results and show how, together with neuroscientific evidence regarding the nature of spatial representation in the brain, they reveal the parallel presence of both egocentric representations and ‘allocentric’ (or ‘geocentric’) representations centered on aspects of the external environment. Further, these results begin to illuminate the complementary contributions to cognition made by egocentric and allocentric representations, and the ways in which they interact.

It has often been argued that the presence of allocentric representations cannot be safely inferred from behavioral results because alternative explanations using solely egocentric representation can often be found [3]. Building upon several elegant experimental findings from their own and other laboratories, Wang and Spelke [2] suggested a simple model of spatial memory that depends upon two types of egocentric process and a ‘geometric module’ 4, 5. The egocentric processes are viewpoint-dependent scene recognition and spatial updating of egocentric locations by self-motion information. The geometric module represents the surface geometry of the surrounding environment, and is used for reorientation of disoriented individuals, but has no direct role in representing object locations. Enduring allocentric representations of location are explicitly absent. Alone among mammals, they argue, humans can go beyond these basic processes by using natural language to combine each with the other, as well as by using artifacts such as symbolic maps.