Figure 1.
Complex cells are less orientation selective than simple cells. A, Spike on/off subfields of an example complex cell examined by cell-attached recording. Top, Arrays of PSTHs for spike responses of the neuron to a set of bright (on) or dark (off) flash squares. PSTHs were arranged in 2-D space according to the locations of corresponding stimuli. Each pixel represents visual space of 5°. Red and green ovals depict the elliptic fitting of the on and off subfields, respectively. Spontaneous firing rate is 1.2 Hz. Scale bars, 20 Hz, 300 ms. Bottom, Color maps for spike on (red) and off (green) responses. The brightness of color represents the average evoked firing rate. The maps were smoothed by bilinear interpolation. The white line depicts the RF major axis, defined by the long axis of the oval. B, Orientation tuning of the same cell. Left, PSTHs for its spike responses to drifting gratings at 12 directions. Red arrow indicates the drifting direction. Scale bars, 20 Hz, 250 ms. Right, Orientation tuning curve of evoked spike numbers. The responses to gratings of opposite directions were averaged for each orientation. Red curve indicates the Gaussian fit. Blue dash line indicates the level of spontaneous spiking rate. C, D, An example simple cell. Data are displayed in a similar manner as in A and B. Spontaneous firing rate is 0.6 Hz. Scale bars: C, 21 Hz, 300 ms; D, 21 Hz, 300 ms. E, Distribution of overlap indices in the recorded cell population. The distribution is significantly bimodal (p < 0.05, Hartigan's dip test). Dash line marks OI = 0.33 (which separates simple from complex cells). F, Depth distribution of the recorded cells. G, Plot of F1/F0 ratio against OI. Blue dash line is the best-fit linear regression line. Correlation coefficient r = −0.74. Black dash lines mark OI = 0.33 and F1/F0 = 1, respectively. H, Plot of OSI against OI. OSI was measured from responses to either drifting gratings (open triangle) or drifting bars (gray dots). Blue dash line is the best-fit linear regression line (r = −0.63). Black dash line marks OI = 0.33. Inset, Comparison of mean OSIs of complex (black, n = 57) and simple (gray, n = 42) cells defined by OI values. ***p < 0.001, two-tailed t test. I, Plot of OSI against rRF measured between on and off subregions (r = −0.59). Black dash line marks rRF = 0, which separates complex from simple cells. Inset, Comparison of mean OSIs of complex (n = 54) and simple (n = 45) cells defined by rRF values. ***p < 0.001, two-tailed t test. J, Plot of tuning width against OI (r = 0.54). Inset, Comparison of mean tuning widths of complex and simple cells defined by OI values. ***p < 0.001, two-tailed t test. K, Plot of tuning width against rRF (r = 0.51). Inset, Comparison of mean tuning widths of complex and simple cells defined by rRF values. ***p < 0.001, two-tailed t test. L, Plot of angle of the major axis of on subfield versus that of off subfield for complex cells (n = 43). Red dash line is the identity line. Note that only complex cells with OSI ≥0.3 were selected. M, Plot of angle of the preferred orientation (measured with drifting gratings or bars) and that of RF major axis (measured with flash squares). Red dash line is the identity line.