THE ELEMENTARY MOVEMENT DETECTION MECHANISM IN INSECT VISION

In insects, the elementary movement detection (EMD) mechanism is based on a nonlinear asymmetric interaction between signals mediated by adjacent points of the sampling lattice of the eye. The nature of this nonlinear interaction is still somewhat controversial: whereas Schmid & Bulthoff (1988) suggested that it is inhibitory, Franceschini et al. (1989) reported that it is facilitatory. Despite the conflicting reports, we show that experimental evidence to date favours an inhibitory interaction. This paper attempts to resolve the conflict by disproving a hypothesis by Franceschini et al. (1989) suggesting that only a facilitatory mechanism can account for the response of a fly wide-field movement-detecting neuron (H1) to sequential stimulation of a pair of adjacent photoreceptors. It is shown here that the responses of a directionally selective movement-detecting neural network architecture, based on lateral inhibitory interactions, match very well the recorded responses of the fly H1 neuron.