A few observations on linking VEP responses to the magno- and parvocellular systems by way of contrast-response functions

It has been proposed that magno- and parvocellular contributions to Visually Evoked Potentials (VEPs) can be isolated, or differentiated, by noting the contrast-response relationships of the responses. This suggestion is examined quantitatively by determining the similarity between various sets of VEP data that have been attributed to the magno- and parvocellular systems and previously reported contrast-response functions for different kinds of neurons (magno- and parvocellular neurons and V1, V4, and MT cells) and combinations of the contrast-response functions for these neurons. It is found that other neurons, or combinations of other neurons, typically give better fits to the data than do magno- and parvocellular cells. Thus, to attribute VEP responses to the magno- or parvocellular systems based on contrast-responses properties faces difficulties.