Fig. 5.

Evolved double opponency. (A) Average receptive field based on random single-opponent responses that led to a strong output response (>0.75) for the best-performing network in the 10 simulated runs of evolution. Values greater than 0.5 indicate a preference for relatively longer wavelengths, whereas values less than 0.5 indicate a preference for relatively shorter ones. The evolved networks were relatively insensitive to inputs from information beyond the central region of the patterns (dashed outline). (B) Radial averages (red circles) of the receptive field that led to strong responses. The blue curve is a maximum likelihood fit to a difference of Gaussians function; error bars show ±1 SE. (C and D) Average receptive field that led to weak responses (<0.25) for the best-performing networks in the 10 simulations. Whether a network evolved a yellow (LM)-ON center (shown here) or a blue (S)-ON center receptive field depended on whether it evolved to match the conditional cumulative probability function of LM or S cone increments or of LM or S decrements. While the evolved double-opponent receptive received input from only one type of single opponent neuron [(LM)-ON neurons], in experimental animals the double-opponent receptive field center is signaled by strong activation arising from the input of one type of spectrally preferring single-opponent neurons and weak activation arising from spectrally opposite preferring type. Conversely, the surround is determined by the opposite input from single-opponent neurons.