Visual scanning behaviour in honeybees
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Freely flying bees were rewarded with sugar solution on a variety of black-and-white shapes as well as on coloured gratings in various training situations (Table 1). In subsequent dualchoice tests, the bees' discrimination between the various shapes was measured. In addition, the bees were video-filmed while flying in front of the shapes. The scanning patterns thus obtained were then quantified in order to (i) characterize scanning behaviour and its relationship to the geometrical parameters of the scanned shapes, (ii) investigate whether scanning plays a role in pattern discrimination and (iii) examine the influence of training on the characteristics of scanning.
The scanning patterns clearly mirror the contours of the scanned shape in all cases (Fig. 3), i.e. the bees fly along the contours contained in the shape. This behaviour does not depend on whether the scanned shape is one that was previously rewarded, or one that is completely novel to the bees.
Comparison of the results of quantifying the scanning patterns with the results of dual-choice tests (Fig. 5) reveals that scanning behaviour is independent of discrimination performance.
On the average, horizontal scanning directions occur more often than vertical directions (Fig. 4).
Variations of the training situation produce measurable differences in scanning behaviour (Fig. 4). However, except in the case of vertical scanning on a vertical grating (Fig. 4), these differences are quite small, indicating that following contours is a largely stereotyped behaviour.
Horizontal gratings are very well discriminated from vertical ones even if they offer contrast to only one receptor type, i.e. blue or green (Fig. 8), demonstrating that the direction of contours is visible to the pattern recognition system even under these conditions. However, vertical and horizontal coloured gratings offering only blue-contrast do not elicit contour-following (Fig. 9 c and d), whereas gratings offering only green-contrast do (Fig. 9 a and b). Thus, the bees' scanning behaviour is colour-blind and most probably governed by the green receptors.
We suggest that contour-following is the byproduct of a behavioural mode which serves to prevent retinal image movement during flight in front of a contoured visual pattern.
KeywordsRetinal Image Stereotyped Behaviour Discrimination Performance Scanning Direction Pattern Discrimination
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