Flies, optic flow and multisensory stabilization reflexes

Abstract

Besides sensing flow in air and water by means of mechanosensory mechanisms, visually oriented animals, including humans, exploit optic flow to control their behavior. The rather intuitive term optic flow has been coined more than six decades ago by J. J. Gibson in his accounts on human visual perception and describes the direction and magnitude of image motion due to movements of the visual system relative to a static environment. Ever since Gibson proposed the potential significance of optic flow for the control of behavioral action, a large number of studies on animal models across phyla were dedicated to identify the neuronal mechanisms underlying the processing of optic flow. A necessary prerequisite for using optic flow to estimate and ultimately control locomotion and balance in space is the capability of the nervous system to analyse the direction of visual motion. In this chapter I will describe fundamental properties of optic flow, review the functional structure of elementary movement detectors which analyse visual motion, and outline how the visual system overcomes notorious problems of local sensor measurements, i.e. their noisiness and ambiguity. I will focus on a specific species, the dipteran blowfly, which has been studied for many years, in particular in the context of multimodal stabilization reflexes, both at the behavioral and neuronal levels.