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Abstract:
Flies improve the efficiency of search for rewarding targets by comparatively simple strategies of orientation which have been studied in fixed flying or free walking animals. The results demonstrate the evaluation of at least three properties of the preferred targets: Proximity. Using motion parallax between figure and ground as a criterion, searching flies are likely to select the nearest targets for exploration. This increases the number of trials per pathlength. Remote figures appear to be embedded in the ground, and do not elicit long lasting curiosity. Novelty. Choice between two or more inaccesible figures can be characterized by a high rate of trials and by an equidistribution of visits, independent of the differences in figure-specific attraction. This is achieved by sustained spontaneous alternation (SSA) of the preferred target. SSA disengages the flies from non-rewarding targets. The strategy is reminiscent of sustained spontaneous depth reversal in human perception of ambiguous figures such as as the Necker cube. SSA is likely to exist in other experimental animals, and may have concealed their ability for pattern discrimination and learning. Ubiquity. The persistence of direction in the trajectories of flies gradually increases with the time spent in the absence of favourable sensory cues. This strategy is reversible and extends the radius of area-covering search by a factor of up to ten until the flies hit upon rewarding targets.
