Psychophysical signatures associated with magnocellular and parvocellular pathway contrast gain: comment.

The recent paper by Pokorny and Smith [J. Opt. Soc. Am. A 14, 2477 (1977)] describes psychophysical data that correlate well with the physiology of the magnocellular and the parvocellular pathways. One of the critical differences between cells in these two pathways is the contrast of the visual input for which the responses of these cells start to saturate. In the analysis of their data, Pokorny and Smith have to assume values for the saturation contrast of the putative pathways that mediate detection. Here I reanalyze their model and show that this assumption is unnecessary, since values of the saturation contrast follow directly from their data.