Fig. 1. The experimental apparatus. (A) Plan view; (B) frontal view. Two shapes, one rewarding (termed positive), the other not (negative), are presented simultaneously, each mounted on a 50 mm-long Plexiglas tube that penetrates its centre and connects the front wall of the apparatus to the reward box fixed behind it. The tube associated with the positive shape is open (A, right) whereas the other ends blindly. After training bees with a particular pair of shapes, they are tested by offering them a choice between the positive shape and each of several novel shapes (discrimination tests) or between a novel shape and other novel shapes (transfer tests), as explained in the text. The first choice of each bee on each of its visits is recorded. Choice frequency (CF), i.e. the percentage of choices for a given shape, is calculated from the sum of choices (N) obtained in each type of test.