Temporal encoding in the visual system

A new model for temporal and spatial encoding in the visual system is developed and presented. The model indicates that spatial information is encoded in a manner similar to the encoding of temporal information. Experimental evidence related to this model is presented and analyzed.

The temporal part of the model has been further developed. The model is based on two integrators in series with a temporal differentiator. The outputs of a varying number of similar, surrounding parallel cells can be pooled together in spatial integration.

The length of the integration time as well as the number of cells spatially pooled together are controlled by the amount of spatial and temporal integrated light falling in and around every point on the retina.

Three series of experiments were conducted to validate the model. The experiments used (1) a TV display of random, dynamic noise and (2) a specially developed stimulus generator which is able to produce very large hom~geneous visual fields which can be easily modulated to reproduce a large variety of temporal waveforms having a rise time longer than 1 msec.

The obtained results support the proposed model. The principal findings are: (1) Time integration of the eye is locally controlled and set across the retina and has very fast dynamics. (2) The obtained CFF curves suggest a correlation between the frequency at which maximum sensitivity is obtained and the sensitivity itself. (3) As predicted by the model, temporal bands are developed in the visual system for stimuli showing temporal discontinuity points. The width of the temporal bands was measured and a strong correlation was found between the temporal band width and the integration time. The width of the temporal bands is a function of the luminance level at which they are produced; it is not dependent on the stimulus slope. The apparent brightness of the temporal band is, however, dependent on the slope of the stimulus.

The present findings about the temporal and spatial integration of the eye-brain system suggest that they work as a fast adaptation mechanism and that they play a central role in visual perception, explaining homogeneously such disparate phenomena as the spatial Mach bands and their assymetry, the Broca-Sulzer effect, and backward masking.

Suggestions about further research are offered.