Spatial and temporal sensitivity of X- and Y-cells in dorsal lateral geniculate nucleus of the cat

Abstract

Spatial and temporal sensitivity of 81 X-cells and 46 Y-cells in the lateral geniculate nucleus of the cats was measured by determining contrast thresholds of single cells to counterphased, sine-wave gratings. The plots of contrast sensitivity (reciprocal of the contrast threshold) as a function of spatial or temporal frequency of the sine-wave grating represent the contrast sensitivity functions. The spatial contrast sensitivity functions were measured at a temporal frequency (counterphase rate) of 2 cycles[c]/s. Contrast sensitivity peaked around 0.5-1.0 c/deg, and decreased at lower and higher spatial frequencies. Temporal contrast sensitivity functions were measured using the spatial frequency to which the cell exhibited the lowest contrast threshold. The shapes of the temporal functions were similar for both X- and Y-cells. The temporal resolution, which was the highest counterphase rate to which the cell responded at 0.6 contrast, was higher for Y-cells than for X-cells within the binocular segment (0-40.degree. eccentricity). In the monocular segment, there was no obvious difference in temporal resolution between X- and Y-cells. For both X- and Y-cells, temporal resolution was fairly constant for all receptive-field eccentricities within the binocular segment. Spatiotemporal interactions were investigated by measuring spatial contrast sensitivity functions at a number of temporal frequencies, in addition to 2 c/s. Grating position within a receptive field was an important factor in the measurement of contrast thresholds for all spatial frequencies for X-cells and for low spatial frequencies for Y-cells. Within Y-cells, the nonlinear subunits exhibited higher spatial and lower temporal resolution than did the linear center/surround portion of the field. Receptive-field center diameter, measured by hand plotting or estimated from area-response functions, correlated weakly with spatial resolution. Area-response functions indicated a strong center-surround antagonism in X-cells and a weak center-surround interaction in Y-cells. This result was related to the different shapes of the spatial contrast sensitivity functions. Y-cells evidently mediate basic spatial pattern vision mainly because of their superior sensitivity to lower spatial frequencies and lack of specificity for stimulus position. X-cells may provide fine spatial detail and position information.