Discrimination of single bars by the honeybee (Apis mellifera)

The bees learn to come for a reward to a very simple pattern, a black bar in a fixed position on a white background, in a Y-choice apparatus, with the targets presented in the vertical plane at a fixed range. They were trained on a number of different arrangements of a single bar on one or both targets. The trained bees were then given appropriate tests to discover what cues they had learned. A cue is an essential parameter that is recognized, not the whole pattern. At the choice point they learn exactly which way to look for consistent cues. After training on a single broad bar versus a blank target, they respond in tests to any area of black where they expect to see it, and are less able to detect it the more it has been displaced from the training position. They are more sensitive to vertical than to horizontal displacement of the bar. The cue is anything black of the right size. They do not recognize the shape or orientation of the bar. When trained to discriminate between two bars at right angles to each other, centred on the reward hole, the cue is the edge orientation at the expected places on the targets, and the bees are less able to discriminate the orientation cues the more they are displaced. When trained on a pair of broad black bars in different positions, the cues are the vertical positions of the centres. Division of the bar into squares, or making the edges stepped, removes the orientation cue but not the position cue. Addition of a large black spot or a checkerboard background to the original bar prevents discrimination, as if the spatial reference frame is disturbed. In training, or testing trained bees, parallax does not assist the discrimination of orientation.