Visual neurons in the lateral geniculate nucleus (LGN) of the cat may be separated into distinct X and Y classes based on a test of the linearity of spatial summation. Y cells produce nonlinear responses especially when the visual stimulus is a fine spatial grating. X cells exhibit mainly linear summation properties. X cells respond mainly at the fundamental modulation frequency of a contrast reversal grating while Y cells respond at the fundamental and at the second harmonic of the modulation frequency. The spatial resolution of X cells' fundamental responses and Y cells' second harmonic responses is about the same, and both are two to eight times higher than the spatial resolution of the Y cells' fundamental response. The conduction velocity of the Y optic tract afferents is greater than that of the velocity of the X afferents. However, the LGN latencies of the responses of the two classes of cells to optic chiasm stimulation overlap considerably.
View details for Web of Science ID A1979HG22000010
View details for PubMedID 477781