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Determining range information from self-motion: the template model

Insects use a relatively simple visual system to navigate and avoid obstacles. In particular they use self motion to determine the range to objects by the angular velocities of the contrasts across the retina array. Adopting principles learnt from studying insect behaviour and neurophysiology we have modelled aspects of the motion detection mechanism of an insect visual system into a means of categorising edges and computing their motion and thus determining range. Copying insect motion perception a camera is scanned across a scene and a temporal sequence of line images captured. The 8-bit grey scale image is immediately reduced to a 1og23 1. 6 bit image by saturating the contrast. Behind each pixel one state is formed by increasing intensity one by decreasing intensity and a third is indeterminate. Pairs of receptors at two consecutive times forming a 2 by 2 template in space-time give a finite number of combinations of which it is found that only a small subset provide useful motion information. Combinations of selected templates results in a distribution of template responses that is amenable to analysis by the Hough transform. Running the model on real scenes reveals the value of lateral inhibition as well as insights into the effect of different edge types and the use of parallax. The model suggests a possible new neurophysiological construction that can be copied in hardware to provide a fast means inferring 3-d structure in a scene where the observer is moving with a known velocity. 1.