Behavioural Analysis of Spatial Vision in Insects

Abstract

Two aspects of spatial visual orientation in insects constitute the central theme of this chapter: The detection of movement and the evaluation of the position of contrast elements in the visual world. In the first section the visual stimulus situation of an insect moving freely in its natural surround is described. The received “flow field” can be decomposed into three components which result from rotatory and translatory self-movement of the animal and from moving objects (e.g. birds). The next section on basic behavioural phenomena outlines the techniques of open- and closed-loop experiments and describes a few simple experiments on visual movement and position detection in flies. On the basis of these experiments an expression is derived which describes the rotatory component of a fly’s flight path through space. The equation is equivalent to the phenomenological equation of Reichardt and Poggio (1976). The third section investigates the basic principles underlying movement and position detection. Comparison of two schemes for movement detection, the gradient scheme and the correlation scheme, with measured behavioural responses demonstrates that the visual system of flies utilises a correlation-based mechanism for the detection of large- field movement. For position detection again two schemes are discussed which are based on flicker detection and movement detection. A final decision on which of the two schemes might be more relevant for fixation and tracking of moving objects by flies seems not yet possible. In the fourth section interactions between elementary movement and position detectors are deduced from behavioural experiments. In the discussion various more sophisticated aspects of visual spatial orientation behavior of insects are reviewed with emphasis on recent literature (1979 & later).