Response properties of X and Y cells. (A) Responses of an X (left) and Y (right) cell to contrast modulated gratings at several spatial positions. At two positions, temporal modulations of the contrast of the grating produce little or no response in the X cell, as the light and dark regions canceled. For the Y cell, the grating produced responses at all spatial positions. This panel is adapted, with permission, from Enroth-Cugell and Robson (1966). (B) Response of a mouse ganglion cell with properties resembling a Y cell to temporal modulation of low and high spatial frequency gratings. Temporal modulation of a single spot produced a strong response at the temporal frequency of modulation (top). Temporal modulation of a high spatial frequency grating produced a temporal response at twice the modulation frequency, that is, a frequency-doubled response. The spatial extent of the ganglion cell dendrites is compared with the gratings in the far left panels.