The dual role of sensory systems: reporting on stimuli and affordances

This paper addresses a long-standing debate concerning the information-conveying function of sensory systems. The debate comes into focus with sensory systems in their most elemental form. These most basic systems consist of structurally distinct receptor (input) and effector (output) units. The receptor element has evolved under selective pressure exerted by an environmental stimulus and the effector has evolved under selective pressure exerted by a positive or negative affordance (a resource or threat). Take, for example, moth auditory systems dedicated to responding to the threat of predation posed by bats: the input side has been shaped by high-frequency sound, while the output (flight response) is adapted to the threat. When a sensory system has been shaped in this way by both a stimulus and an affordance, we face a question fraught with controversy. Does the system have the job of reporting on the stimulus or the affordance? Karen Neander has argued convincingly that the viewpoint from mainstream cognitive science supports the stimulus answer. The aim of this paper is to show that basic sensory systems also channel information about affordances. The argument of the paper draws on foundational assumptions of sensory ecology, a branch of biology concerned with the informational needs of organisms and how organisms have evolved to satisfy these needs. The viewpoint from sensory ecology complements the perspective familiar from cognitive science, revealing a critical role for sensory information about affordances.