Spatiotemporal Coupling and Scaling of Natural Images and Visual Sensitivity

The visual system is concerned with the perception of objects in a dynamic world. A signi cant fact about natural time-varying images is that they do not change randomly over space-time; instead image intensities at di erent times and/or spatial positions are highly correlated. We measured the spatiotemporal correlation function { equivalently the power spectrum { of natural images and we nd that it is non-separable, i.e., coupled in space and time, and exhibits a very interesting scaling behaviour. When expressed as a function of an appropriately scaled frequency variable, the spatiotemporal power spectrum is given by a simple power-law. We point out that the same kind of spatiotemporal coupling and scaling exists in human visual sensitivity measured in psychophysical experiments. This poses the intriguing question of whether there is a quantitative relationship between the power spectrum of natural images and visual sensitivity. We answer this question by showing that the latter can be predicted from measurements of the power spectrum. To whom correspondence should be addressed. Email: [email protected]