Visual consciousness revisited: magnocellular and parvocellular contributions to conscious and nonconscious vision

Current theoretical approaches to consciousness and vision associate the dorsal cortical pathway, in which magnocellular (M) input is dominant, with nonconscious visual processing and the ventral cortical pathway, in which parvocellular (P) input is dominant, with conscious visual processing. We explored the known differences between M and P contrast-response functions to investigate the roles of these channels in vision. Simulations of contrast-dependent priming revealed that priming effects obtained with unmasked, visible primes were best modeled by equations characteristic of M channel responses, whereas priming effects obtained with masked, invisible primes were best modeled by equations characteristic of P channel responses. In the context of current theoretical approaches to conscious and nonconscious processing, our results indicate a surprisingly significant role of M channels in conscious vision. In a broader discussion of the role of M channels in vision, we propose a neurophysiologically plausible interpretation of the present results: M channels indirectly contribute to conscious object vision via top-down modulation of reentrant activity in the ventral object-recognition stream.