Figure 6.

Pooling indices. The pooling index (Equation 8) describes how a pair of image statistics interact: It is the ratio of the thresholds when they have opposite signs, to when they have the same sign; values larger than one indicate cancellation in the opposite-sign condition. For individual subjects, pooling index is calculated from all trials. For the group means, the pooling index is calculated from all trials (solid bar), and for the subsets of trials separated according to whether the background was structured or the target was structured. N = 6 for pairings within order (second- or third-order), N = 4 for pairings between orders.