Figure 2

Tuning amplification and contrast invariance of neuronal responses in the network. (A) The random network (center), composed of excitatory (red, 80%) and inhibitory (blue, 20%) neurons, transforms weakly tuned input (green) to highly selective responses (red). The sample tuning curves are shown for unit # 4715, which is an excitatory neuron. Neurons have very similar tuning curves for different contrasts, and they are indistinguishable after normalization by their respective peak value (see inset). EPSP = 0.1 mV. (B) Spikes elicited by the same excitatory neuron as in (A) in response to different orientations of a stimulus at a medium contrast. (C) More samples of output tuning curves from the network, in polar representation. Radial axis encodes the firing rate of the respective neuron at each orientation, indicated by the angle, with the maximum firing rate indicated as a number next to each plot. Both excitatory (red) and inhibitory (blue) neurons are highly selective in their responses, despite their weakly selective inputs (green) and recurrent inputs of mixed selectivities. Lighter colors correspond to tuning curves for lower contrasts, respectively.