PROCESSING BY HUMAN VISUAL-SYSTEM OF LIGHT AND DARK CONTRAST COMPONENTS OF RETINAL IMAGE

A response phenomenon, the frequency shift effect, was studied with particular attention to the most suitable parametric description. Previous investigations of the effect showed that the perceived spatial frequency of a test grating pattern could be changed, transiently, after a period of adaptation to a grating of different frequency. The perceived width of the bars of 1 polarity (i.e., light or dark) in the test grating could be changed independently of the width of bars of the opposite polarity in the test grating and in the adaptation grating. There was no simple interpretation of this result in terms of the spatial frequency spectra of the gratings. The human visual system may process positive and negative contrast polarities in independent channels. The results were discussed in relation to the on- and off-center receptive field characteristics obtained in microelectrode recordings from vertebrate visual systems.