Fig. 4. Results of Expt 2, shape discrimination and generalization from luminance contrast to colour contrast and motion contrast. Bees were trained with a black diamond (positive) versus a black disc (negative) placed against a white background (inset). (A) The black-and-white bar on the left shows the choice frequency (CF) obtained during the training. Bees were then given transfer tests with a diamond vs a disc, which were both either blue or yellow, again on the white background (blue and yellow bar, respectively, with a white margin), and with black, blue and yellow shapes placed on a patterned background (bars with patterned margins). (B) Bees choosing between the learned diamond and a novel shape, a square, placed on a white background. The pair of test shapes is black, blue or yellow. (C) Control tests showing that the bees' choice behaviour constitutes a generalization performance, as explained in the text. In all three panels, the total number of choices (N) on which the CFs are based is given above each bar.