A simulated human fovea: the L-type cells of the magnocellular pathway.

A static model of the human fovea is used to study the properties of L-type amacrine cells (L-AC) that link the cones with the magnocellular pathway. Sine and square wave gratings are used to obtain response spectra of L-ACs and C-type bipolar cells (C-BC); these two types of cells are compared in both central fovea, where there are no blue-sensitive cones and parafovea, where the blue-sensitive cones 12% of the population. Three dispersion conditions are used: no, aberration-free, and chromatic dispersions. The abilities of L- and C-type cells to resolve a two-bar image are also compared. The findings are consistent with the magnocellular pathway having higher contrast luminance and chromatic sensitivity gains than those of the parvocellular pathways, but under specified conditions. And under specified conditions the findings are also consistent with both pathways being involved in the detection of chromatic and achromatic signals. Nevertheless when all factors are considered the parvocellular pathway appears to be involved with fine spatial and chromatic tuning while the magnocellular pathway appears to deal with coarser tuning.