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Fig. 9.5. Distribution of orientation preferences in animals and in HLISSOM. The thin line with circles delineates a histogram of orientation preferences for a typical adult ferret visual cortex (replotted from Coppola et al. 1998; measured through optical imaging in an oval 8.4 mm × 3.3 mm area). The thick line shows a similar histogram for the "ND+Nature" network from Figures 9.3, 9.4, and 9.6. Both adult ferrets and the HLISSOM model have more neurons representing horizontal or vertical than oblique contours, reflecting the statistics of the natural environment. HLISSOM maps trained on internally generated patterns alone instead have an approximately flat distribution, as seen in the histograms of Figure 9.1.