Two methods for calculating the responses of photoreceptors to moving objects.

The responses of photoreceptor cells to moving stimuli are crucial to understanding motion detection in visual systems. However, these responses are not well characterized quantitatively because they result from a combination of spatial optical behavior in the lens systems with temporal behavior in the phototransduction mechanism. While both these processes can now be modeled quite well by relatively simple equations, their combination cannot be easily obtained in a closed form. Here, we present two approaches to this problem, based on well-established models for the lens and photoreceptors systems of the fly compound eye. The first approach leads to a recursive formula for predicting the photoreceptor response to a moving point object. The second method is approximate, but almost equally accurate and more rapid.