Figure 7.

Spatial properties: contrast dependency. Besides the effect on OFR magnitude just reported (Figure 6), contrast also affects the interaction index. Here we compare responses to 8% and 64% stimuli. The responses to strip pairs (top panels) and the interaction index (bottom panels) are shown, as a function of the separation of the strips. OFRs to strip pairs essentially scaled with contrast. However, contrast did not simply rescale all responses: Lowering the contrast of the stimulus reliably increased the value of I_I, so that suppression observed at high contrast was either reduced or even replaced by facilitation. Error bars indicate ±SEM. The responses to strip pairs are fitted with a cubic polynomial, whereas for the interaction index we used the exponential function.