Figure 4.
Opponent cells in superior retina showed relatively balanced M/S antagonism. A, Response waveforms (PSTHs, in blue) of an S+/M− opponent cell from superior retina in response to flashed monochromatic spots (diameter ∼850 μm; flash duration 300 ms; flash onset at 100 ms in the plots). Same format as Figure 2C. The flash intensities were 3.99 × 104, 5.68 × 104, 3.23 × 104, and 2.40 × 105 quanta/μm2/s (440, 460, 530, and 610 nm). The response amplitudes were measured from the fitted waveforms at either flash onset or offset, depending on the polarity of the response (see Appendix A). The background produced 4.11 (M), 4.06 (S), and 4.70 (Rod) log10 Rh*/photoreceptor/s. Data shown are from the first block of trials for this cell. B and C also show data from this block of trials for the same cell and background intensity. The morphology of this cell is shown in the second panel from top in Figure 7A. B, Flash contrast-response function. Response amplitudes of either ON (solid gray circles) or OFF (solid blue circles) responses to monochromatic flashes of wavelengths from 420 to 620 nm were fitted with two static nonlinearities (solid red line for ON responses; dashed red line for OFF responses) as described in Appendix B. The x-axis of the plot is the weighted input contrast, Cinput, derived from the model fit (see Eq. B1 in Appendix B). C, Action spectrum of an S+/M− opponent cell in superior retina. The same data as in B are plotted as a spectral sensitivity. The solid and dashed red lines represent the magnitude of the weighted sum of M, S, and rod contrast sensitivities as determined by the model fit. The solid line represents the wavelength region where there was an ON response, while the dashed line represents the wavelength region where there was an OFF response. The relative photopigment weights used to produce the action spectrum were M: −0.41, S: 0.58, and rod: −0.02 and are shown by the horizontal bars in the inset (magnitudes of the M, S, and rod weights are represented by green, blue, and gray bars). Sensitivity dropped significantly between 460 and 480 nm, indicating the spectral neutral point (see also Fig. 3). The overall shape of the action spectrum here and in F resembles the guinea pig increment-threshold spectral sensitivity measured behaviorally by Jacobs and Deegan (1994). The vertical location of the data points on the spectral plots has been corrected for variation in stimulus intensity across wavelength and for the shape of the cells' ON and OFF static nonlinearities (see Appendix B) (Yin et al., 2006). D, Response waveforms (PSTHs, in blue) of an M+/S− opponent cell from superior retina to flashed monochromatic spots (diameter ∼850 μm; flash duration 300 ms). Same format and background intensity as A. The flash intensities were 3.42 × 104, 5.08 × 104, 2.96 × 104, and 2.12 × 105 quanta/μm2/s (440, 460, 530, and 610 nm). Data shown are from the first block of trials for this cell. E and F also show data from this block of trials. The morphology of this cell is shown in the second panel from top in Figure 7B. E, Flash contrast-response function. Same format as B. F, Action spectrum of an S+/M− opponent cell from superior retina. Same format as C. The relative weights were M: 0.42, S: −0.51, and rod: 0.07 and are shown in the inset. Because the response amplitude to the flash at 470 nm was zero, no data point is plotted for that wavelength.