Temporal decorrelation: a theory of lagged and nonlagged responses in the lateral geniculate nucleus

Natural time-varying images possess significant temporal correlations when sampled frame by frame by the photoreceptors. These correlations persist even after retinal processing and hence, under natural activation conditions, the signal sent to the lateral geniculate nucleus (LGN) is temporally redundant or inefficient. We explore the hypothesis that the LGN is concerned, among other things, with improving efficiency of visual representation through active temporal decorrelation of the retinal signal much in the same way that the retina improves efficiency by spatially decorrelating incoming images. Using some recently measured statistical properties of time-varying images, we predict the spatio-temporal receptive fields that achieve this decorrelation. It is shown that, because of neuronal nonlinearities, temporal decorrelation requires two response types, the lagged and nonlagged, just as spatial decorrelation requires on and off response types. The tuning and response properties of the predicted LGN cells compare quantitatively well with what is observed in recent physiological experiments.