Figure 7.  Representation of a selective attention task in which a pigeon categorized rectangles depending on whether they were narrower or wider than a fixed criterion width. Top panel: Two contours of equal likelihood are shown for each category. For each category, the smaller and larger circular contours are 1 and 2 s.d.’s from the mean (filled circle) of the corresponding normal bivariate distribution. Bottom panel: The two exemplars corresponding to the means of categories B and A, respectively. See Figure 3 and related text in Herbranson, Fremouw, and Shimp (1999) for additional details.