Modelling the temporal response properties of an insect small target motion detector

Abstract

Insects are an excellent model system for investigating computational mechanisms evolved for the challenging task of visualising and tracking small moving targets. We examined a well categorised small target motion detector (STMD) neuron, the dragonfly centrifugal STMD 1 (CSTMD1). This neuron has an unusually slow response onset, with a time course in the order of hundreds of milliseconds. A parsimonious explanation for this slow onset would be temporal low-pass filtering. However other authors have dismissed this and instead proposed a facilitation mechanism derived from second order motion detectors. We tested the spatial locality of response to continuous motion on non-contiguous paths and found spatial discontinuities in otherwise continuous motion reset the neuronal response. We modelled an array of elementary motion detectors (EMDs) in the insect visual pathway. We found that whilst individual components of the response can be explained simply by modifying the properties of the EMDs, the neurons response considered as a whole requires further elaborations within the system such as the proposed second order motion pathway.