(A,B) Spatial sensitivity of magno- (A) and parvo-cellular neurons (B) as a function of the ratio between the strengths of their center and surround. The responses of both M and P cells were re-normalized to the maximum of the behavioral CSF (curve labeled "Human", replotted from ) Figure 1A for comparison purposes. 'DL' and 'CK' label the ratios measured experimentally by Derrington and Lennie (1984) and Croner and Kaplan (1995) respectively, from the medians of their reported values. All other parameters were set as described in the Materials and methods section. (C, D) Full parametric analysis of the difference in slope at low spatial frequencies between the human CSF and the spatial sensitivity of difference-of-Gaussians models. Each point in the map shows the slope deviation resulting from a particular ratio between surround and center amplitudes (, horizontal axis) and between radii (, vertical axis) in the models (Equation 3). A value of zero represents perfect matching between the CSF and the receptive fields profile; negative/positive values indicate that the neuronal filter is less/more attenuated than the CSF. Values of the parameters for which the slope could not be computed because the receptive field did not exhibit a band-pass behavior are indicated by white. The magenta and greed dots mark parameters measured experimentally by Croner and Kaplan (1995) and Derrington and Lennie (1984) respectively (dashed lines). (D) Ratio between center/surround excitation and inhibition. A value of 1 indicates that center and surround have the same strength. Legends and symbols are as in C. Comparison of panels C and D shows that a slope similar to that of the human CSF can only be obtained for close balance between excitation and inhibition. These values differ greatly from those measured experimentally (magenta dot).