Visual discrimination of radial cues by the honeybee (Apis mellifera)

This is a systematic study of the discrimination of black radially symmetrical patterns presented on a white vertical background and subtending 45° or 50° at the point of choice in a Y-maze apparatus. Before discrimination can occur, the ability to fixate is promoted by any radial pattern irrespective of the number of symmetry axes. A ring of spots can also stabilize the eye before the positions of the spots are discriminated. Cues for discrimination are of two main types. First, with fixed patterns of sectors or spots, the cue is the location of an area of black relative to the fixation point, and the particular number of axes is less important than the size of the individual areas. Secondly, evidence is presented for a family of filters with large fields and coarse tuning that detect patterns of radially symmetrical edges. These filters become more evident when the patterns are made of thin black radial bars or when they are rotated at random during the training. An angular shift of one radial pattern relative to the other, or a difference between numbers of bars, is best discriminated when one of the patterns but not the other has angles of 30°, 60°, or 120° between radial edges, and least when the angles are 90°. Baffles in the apparatus make the bees pause and fixate so that discrimination is improved. When targets are rotated during the learning process, radial cues for discriminations must be presented as edges, not as spots or areas. Besides detecting and fixating flowers, this system could be useful to estimate the perfection of their symmetry.