The magnocellular system versus the dorsal stream

In his opinion paper, Breitmeyer (2014) sought to identify the contributions from the magnoand parvocellular systems to conscious and unconscious vision. One approach employed in this attempt was to study the effect of contrast. This was based on the well established finding that magnoand parvocellular cells differ in their contrast-response functions (Kaplan and Shapley, 1986): Magnocellular responses increase rapidly with contrast at low contrast levels but saturate at medium contrasts. Parvocellular responses, on the other hand, increase with contrast at a relatively constant rate. In his Figure 5, Breitmeyer makes the suggestion based on the effect of contrast, that visible priming reflects magnocellular activity whereas invisible priming reflects parvocellular responses. In Figure 1 is shown (solid line) the function: