Spectral reflection curves of the stimuli used in our experiments and relative absorptions of the three honeybee’s photoreceptors, S, M and L (shown in gray). The colors distances between these colors in two perceptual spaces proposed for the honey bee, the color hexagon (Chittka, ) and the color opponent coding space (Backhaus, ) were high enough as to allow discrimination in all cases (Dyer et al., ; see Table ).

Training and testing procedure. The bees had to choose between stimuli varying only in size. At each foraging bout, the bees faced stimuli of two different sizes taken randomly between the six available sizes (from 1 to 6 cm with 1 cm step). Depending on testing group, the smallest or the largest stimuli were rewarded with a sucrose solution while the alternative stimuli were associated with a quinine solution. Each stimulus was presented twice. Four stimuli (two identical S+ and two identical S−) were then simultaneously offered to the bees. During training, stimuli shapes and size combinations varied to facilitate concept learning. Once training was completed, the bees were subjected to non-rewarded transfer tests intermingled with refreshing training trials. Note that only a subset of all possible tests was proposed to each bee (see text for details). The insert show a representation of the rotating screen on which the four stimuli are vertically presented in a random spatial organization (Dyer et al., ).

Performance of the tested honeybees. Percentage of correct choices in the training (left panel) and tests (right panel) phases. Performance of the bees rewarded on the larger stimuli are presented in black while performance of the bees rewarded on the smaller stimuli are presented in white. The dashed line indicates chance level performance. Data shown are means +s.e.m. n = 26 for the acquisition curve and learning test. 10 of the 26 bees were tested in the “blue stars transfer test” while the others were tested in the “violet stars transfer test” (***: p < 0.001; n.s: p > 0.05).