THEORETICAL PREDICTIONS OF SPATIOTEMPORAL RECEPTIVE-FIELDS OF FLY LMCS, AND EXPERIMENTAL VALIDATION

1. A theory is presented that utilizes the structure of natural images, and how they change in time, to produce spatiotemporal filters that maximize information flow through a noisy channel of limited dynamic range. For low signal-to-noise ratios (SNRs) the filter has low-pass, and for high SNRs band-pass characteristics, both in space and time. 2. Theoretical impulse responses are compared to measurements in Large Monopolar Cells (LMCs) in the fly (Calliphora vicina) brain. Two different spatial stimuli (point source and wide field) were given at background intensities over a 5.5 log unit wide range. Theory and experiment correspond well, and they share the following properties: impulse responses get much faster and more biphasic with increasing background intensity (SNR); they show larger off-transients for wide field stimuli than for point sources; the half-width of the spatial receptive field changes only slightly with increased intensity, and lateral inhibition increases; contrast efficiency increases with intensity.