A new cue for visual discrimination by the honeybee has been demonstrated. Bees detected the position of the centre of symmetry of radial patterns of spokes, sectors, and circles relative to their point of choice in the learning process, irrespective of the pattern. When trained with one of these patterns versus a blank target, the bees discriminated a shift in the position of the centre of symmetry by as little as 5°, in some cases with unfamiliar test patterns. A pattern of spokes or rings also stabilized the vision of the bees in the horizontal plane so that the position of a plain black area could then be discriminated. In other experiments, bees discriminated half of a pattern of radial spokes or concentric circles from the other half, cut either vertically or horizontally, and irrespective of scale. Therefore these patterns were not detected by preformed combinations of orientation detectors or global templates with a single output. Instead, the crucial cue for detecting edges as radial or circular was the coincidence of responses of numerous local edge detectors having the appropriate convergence to a hub. Edges that converged towards a hub were detected by the bees as radial, and edges at right angles to these were parts of circles, irrespective of the actual pattern. Breaking the patterns of spokes or circles into rows of squares spoiled the discrimination if the squares were separately resolved. Alternatively, breaking the pattern into short bars that were separately resolved spoiled the discrimination when the bars subtended less than 3°. The local feature detectors for spokes and circles therefore resembled those of the orientation detectors in being short, independent, and unable to span gaps of more than 3°. In conclusion, radial and circular patterns were identified by the regional coincidences and convergence of local detectors of edge orientation, and the positions of the centres of symmetry were remembered as landmarks that helped locate the reward, but the patterns themselves were not remembered. © 2006 Elsevier Ltd. All rights reserved.
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