Example 551

As a first example of calculating the effects of LI predicted by the model, assume k(x) = ko exp(-a |x|). (As noted above, experimental workers have found that K decreases with the interommatidial distance parameter, x.) Thus, K(u) = 2 a ko/(u2 + a2), and from Equation 5.3-8, L(u) = (u2 + a2)/(u2 + 2ako + a2). This L(u) attenuates the E-cell rate of firing, r(x), for low spatial frequencies; thus, for u < -^2ako + a2 ,

To examine the behavior of this model further, let the input be a general dc level of illumination, B, plus a bright spot over x = 0. That is, e(x) = B + AS(x). Fourier transforming yields

E(u) = J B exp(-jux) dx + J A 5(x)exp(-jux)dx = 2n B 5(u) + A 5.3-9 Now one can use the inverse Fourier transform to find r(x). Clearly, R(u) = L(u) E(u).

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