When interpreting a visual scene, deciding where one object ends, and where the next one starts is the first step. The process of finding the contours of objects is independent of colour information, typically relying on a single, typically longer wave sensitive, photoreceptor. Here, we investigated the possible advantages of this widely described phenomenon, using bees as a model system.
Bees acquire their entire nutrition from flowering plants, and the successful reproduction of those plants hinges on pollination provided by the bees. The strongly mutualistic nature of this plant-pollinator relationship means that evolutionary pressures on both parties act upon the bee’s ability to locate and recognise flowers quickly and efficiently. This provides us with a straightforward model system for studying visual detection mechanisms. Accordingly, we modelled the visual system of bees, and estimated the electrical signals their receptors will generate in response to the light reflected from various flowers.
(click image to enlarge)
Figure: A Mertensia ciliata flower pasted over its leaf, as it appears to human observers, to bees (false coloured image), and the responses produced by the bee's photoreceptors when viewing the image.
We found that when viewing leaves and flowers long-wavelength receptors (peak sensitivity at ~544 nm, i.e. green) generate the most consistent signals with the highest signal-to-noise ratios. Thus, these receptors provide the bee with the most reliable information for identifying whether an object is a flower or a leaf. This result offers an adaptive explanation for using the long-wavelength channel in the initial steps of interpreting a visual scene and highlights a striking example of how ecology and receptor-level processes can shape a visual system.
Reference
Multispectral images of flowers reveal the adaptive significance of using long-wavelength-sensitive receptors for edge detection in bees. Vera Vasas, Daniel Hanley, Peter G. Kevan, Lars Chittka. Journal of Comparative Physiology A, 2017, Volume 203, pp 301–311.