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Illumination as a contextual cue to color choice behavior in bumblebees.
The principle challenge faced by any color vision system is to contend with the inherent ambiguity of stimulus information, which represents the interaction between multiple attributes of the world (e.g., object reflectance and illumination). How natural systems deal this problem is not known, though traditional hypotheses are predicated on the idea that vision represents object reflectance accurately by discounting early in processing the conflating effects of illumination. Here we test the merits of this general supposition by confronting bumblebees (Bombus terrestris) with a color discrimination task that can only be solved if information about the illuminant is not discounted, but maintained in processing, and thus available to higher-order learned behavior. We show that bees correctly use the intensity and chromaticity of illumination as a contextual cue to guide them to different target colors. In fact, we trained bees to choose opposite – rather than most similar – target colors after an illumination change. This performance cannot be explained with a simple color constancy mechanism that discounts illumination. Further tests show that bees do not use a simple assessment of the overhead illumination, but the spectral relationships between a floral target and its background. These results demonstrate that bees can be ‘color constant’ without discounting the illuminant; that in fact they can use the illumination itself as a salient source of information.
Lotto, R.B. and Chittka, L. (2005)