Mach bands: how many models are possible? Recent experimental findings and modeling attempts.

Mach bands are illusory bright and dark bands seen where a luminance plateau meets a ramp, as in half-shadows or penumbras. A tremendous amount of work has been devoted to studying the psychophysics and the potential underlying neural circuitry concerning this phenomenon. A number of theoretical models also have been proposed, originating in the seminal studies of Mach himself. The present article reviews the main experimental findings after 1965 and the main recent theories of early vision that have attempted to account for the effect. It is shown that the different theories share working principles and can be grouped into three classes: (a) feature-based; (b) rule-based; and (c) filling-in. In order to evaluate individual proposals, it is necessary to consider them in the larger picture of visual science and to determine how they contribute to the understanding of vision in general.