Efficient coding of natural time varying images in the early visual system.

We investigate the hypothesis that the early visual system efficiently codes natural time varying images, first by tracking part of the image, then by matching the spatiotemporal properties of the neural pathway to those of the tracked image. A representation for the time varying image is formulated which consists of two spatiotemporal components, a velocity field component and a stationary component. We show, using digitized sequences of natural images, that the spatiotemporal spectrum and other attributes of the image markedly differ before and after tracking. The temporal frequency bandwidth and velocity distribution of the velocity field component are diminished in the region of tracking and broaden with increasing eccentricity from this region. On the other hand, the spectrum of the stationary component is unaffected by tracking. Comparison of the properties of the tracked image to those of the M and P pathways suggests that each pathway transmits different attributes of the tracked image. A retinal architecture which varies with eccentricity also matches the properties of the tracked image.