Figure 4. Putative receptive-field maps obtained with the regularized pseudoinverse procedure (see Materials and Methods). Examples from three different cells (A–C) are shown. On the left is the reverse-correlation map (Revcorr) and its two-dimensional Fourier transform, as in Figure 2 (cell in A is the same as Fig. 2 B). For each cell, receptive-field maps (Reginv) are shown after calculation with five different values of the regularization parameter λ, with their two-dimensional Fourier spectra below. When λ is relatively small (left), the fields are dominated by high spatial-frequency noise; when λ is relatively high (center), there is less noise but the fields seem blurred. However, a basic localized and oriented map is visible in all of the reconstructions, and a localized spectral feature is also clearly discernible. When λ is very high (right), the map becomes very blurred, loses the localized features, and is dominated by one polarity. A, The receptive-field maps are 21.5° square; the Fourier transforms measure ±0.70°-1 square. B, The receptive-field maps are 28.7° square; the Fourier transforms measure ±0.52°-1 square. C, The receptive-field maps are 19.8° square; the Fourier transforms measure ±0.76°-1 square.