Click on the image to see a PDF version (for zooming in)

Fig. 15.2. Scaling retinal density. Each column shows a LISSOM orientation map from one of three matched 96 × 96 networks with retinas of different densities. The parameters for each network were calculated using Equation 15.2, and each network was then trained independently on the same random stream of input patterns. The size of the input pattern in retinal units grows as the retinal density is increased, but its size as a proportion of the retina remains constant. All of the resulting maps are similar as long as R is large enough to represent the input faithfully, with almost no change above R = 48. Thus, a low value can be used for R in practice. Such scaling of retinal density is useful for modeling species and areas with higher receptor resolution, and for matching the cortical magnification factor of a model to that of a particular species.