Parallel Convergences: A Glimpse To The Magno- And Parvocellular Pathways in Visual Perception

Carlo Aleci, Elena Belcastro

The processing of an image, which begins in the retina and continues on the cortex, is provided by two distinct, parallel cellular pathways: the parvocellular (P-) or sustained system, and the magnocellular (M-) or transient system. The P-system is made of small ganglion cells and arranged in receptive fields of small size. In turn, the M-system, is made of larger ganglion cells making up wider receptive fields. Like their anatomical features, also the information carried by the M- and P-cells is different and basically complementary, at least at the subcortical level. A common opinion in the last decades supports the idea that a model based on this parallel M/P complementary processing of the image may account for the various aspects of visual perception. Yet, tracing separately M- and P- information beyond the striate cortex turns difficult due to the diffuse anatomical crossroads, functional intermixing, and to the overlapping of the psychophysical response. The present paper aims at making the point on this issue, pinpointing the already reported caveat for an attractive, albeit probably too simplified (and therefore potentially misleading) schematization.