Processing by the human visual system of the light and dark contrast components of the retinal image

摘要

The investigation is concerned with the processing of light and dark bar patterns by the human visual system. A response phenomenon, the frequency shift effect, is studied with particular attention being given to the most suitable parametric description. Previous investigations of the effect showed that the perceived spatial frequency of a test grating pattern can be changed, transiently, after a period of adaptation to a grating of different frequency. In the present work it is shown that the perceived width of the bars of one polarity (i.e. light or dark) in the test grating can be changed independently of the width of bars of the opposite polarity both in the test grating and in the adaptation grating. It is shown that there is no simple interpretation of this result in terms of the spatial frequency spectra of the gratings. It is suggested that the human visual system processes positive and negative contrast polarities in independent channels. The results are discussed in relation to the on- and off-centre receptive field characteristics obtained in microelectrode recordings from vertebrate visual systems.