Abstract
Many researchers have attempted to use suprathreshold contrast stimuli of low or high spatial frequencies to selectively stimulate (or bias stimuli for) the magnocellular or parvocellular subcortical visual pathways. While this can be done at contrast threshold, the possibility of doing so at suprathreshold contrasts is less clear and is reviewed here. Research on monkeys indicates that (1) magno-and parvocellular neurons are similar when compared at the same visual field eccentricity. Also, (2) koniocellular neurons seem comparable to magno-and parvocellular cells with regard to spatial properties. In addition, (3) cortical neurons are highly selective for spatial frequencies making it possible that response differences associated with high and low spatial frequencies reflect cortical rather than subcortical factors. It is concluded, that the manipulations of spatial frequency in suprathreshold stimuli provides a poor means for separating the magnocellular and parvocellular systems.
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