Summary

At every moment, the natural world presents animals with two fundamental pragmatic problems: selection between actions that are currently possible, and specification of the parameters or metrics of those actions. It is commonly suggested that the brain addresses these by first constructing representations of the world on which to build knowledge and make a decision, and then by computing and executing an action plan. However, neurophysiological data argues against this serial viewpoint. In contrast, it is proposed here that the brain processes sensory information to specify, in parallel, several potential actions that are currently available. These potential actions compete against each other for further processing, while information is collected to bias that competition until a single response is selected. The hypothesis suggests that the dorsal visual system specifies actions which compete against each other within the fronto-parietal cortex, while a variety of biasing influences are provided by prefrontal regions and the basal ganglia. A computational model is described which illustrates how that competition may take place in the cerebral cortex. Simulations of the model capture qualitative features of neurophysiological data and reproduce various behavioural phenomena.

Introduction

At every moment, the natural environment presents animals with many opportunities and demands for action. The presence of food offers an opportunity to satiate hunger, while the appearance of a predator demands caution or evasion. An animal cannot perform all of these behaviours at the same time because they often share the same effectors (you only have two hands; you can only transport yourself in one direction at a time, etc.). Thus, one fundamental issue faced by every behaving creature is the question of action selection. That question must be resolved, in part, by using external sensory information about objects in the world, and in part, by using internal information about current behavioural needs.