Information over function: a reappraisal of the perception-action model

Abstract

In the influential perception-action model, the ventral visual system of the primate brain serves to obtain knowledge of objects in the environment, while the dorsal system serves to control actions in interaction with those objects. In recent years, criticism of the model has gained momentum following reports of evidence that involvement of the two systems may not principally depend on whether observers are engaged in action or perception tasks. This thesis appraises the perception-action model over the course of five experiments that test a number of the model’s central assertions. Evidence for an alternative functional characterization of the dorsal and ventral systems is obtained. Specifically, the evidence suggests that the dorsal system can be involved in both action and perception on the basis of fast egocentric information pickup, while the ventral system can be involved in both perception and action on the basis of slower allocentric information pickup. This raises the possibility that a more fundamental distinction pertains to the characteristics of information pickup by the two systems rather than to the behavioral functions subserved. The thesis develops a stance in which involvement of the two systems in the visual guidance of behavior is dependent on their operational characteristics in combination with the constraints of the task. The proposed relevant task constraints are: (i) whether tasks allow for egocentric and/or allocentric information pickup, (ii) the amount of time that is available for information pickup in a task and, possibly, (iii) whether stimuli are located within or outside functional space (the space that affords action for an observer). Whether a task requires an immediate or a delayed response is of less importance. It is argued that while the typical requirements of perception and action tasks bring about a tight coupling between perception and the ventral system and action and the dorsal system, this coupling is not invariant; perception can involve fast egocentric information pickup and action can involve slower allocentric information pickup. The findings are discussed in the context of higher-level theories of visual perception. It is proposed that the view of the dorsal and ventral visual systems that is suggested by the findings presented in this thesis corresponds better with ecological than with constructivist approaches to visual perception.