THE DETECTION AND RECOGNITION OF COLOR STIMULI BY HONEYBEES: PERFORMANCE AND MECHANISMS

ABSTRACT

In a detection paradigm, honeybees Apis mellifera were trained to distinguish between the presence and the absence of a rewarded colored spot, presented on a vertical, achromatic plane in a Y-maze. In a recognition paradigm, bees were trained to distinguish between a trained colored disk and alternative stimuli differing in their green contrast and/or chromatic contrast. Results from the first experimental paradigm allowed the establishment of α_min, the visual angle subtended by a colored target at the bee eye at which the bees detect a given stimulus with a probability P _o = 0.6. This angle was 5° for stimuli presenting both chromatic contrast and green contrast, and 15° for stimuli presenting chromatic but no green contrast. Therefore, green contrast contributes decisively to the detection task. Results from the second experimental paradigm showed that chromatic and green contrasts are alternatively used depending on the visual angle subtended by a trained chromatic target and that bees also learn the green-contrast difference between a trained and a nonrewarded alternative. Finally, when trained at different visual angles with an achromatic stimulus providing green contrast, bees were capable of learning and detecting the achromatic target only for visual angles from 10° to 5°. Thus, green-contrast and chromatic-contrast channels are tuned to signals of different angular sizes: the chromatic channel conveys the signals of objects of large angular size, while the green contrast channel conveys those of objects of reduced angular size.