Visual illusions are both fascinating and useful for understanding the sensory and cognitive processes involved in perception. Interspecies comparisons of perceptual illusions, in particular, are interesting because they allow insight into the evolution of visual strategies. Here we investigate the Ebbinghaus illusion, a size illusion, which is well know in human perception: a central dot appears larger/smaller when surrounded by smaller/larger dots (see Fig. 1). It is thought to result from computing the size of an object in relation to it’s surrounding, a crucial step towards size constancy.
Previous studies found that bees use the optic flow field in order to analyse an objects 3D shape¹. But what kind of strategy do bees use for the computation of object size? And do bees posses concepts like “smaller” and “larger” ? The existence of the Ebbinghaus Illusion in honeybee vision was tested in a serious of behavior experiments. Our results show that (1) bees can learn and use the concept of “smaller” and larger”; (2) the bees size perception is indeed fooled by the Ebbinghaus arrangement. We conclude that bees compute the relative, and not the absolute size of objects, whereby the underlying neuronal computations take into account the relations to other objects in the surrounding, ultimately enabling size constancy.

References:

Werner,A., Stürzl, W., Zanker, J. (2016). Object Recognition in Flight: How Do Bees Distinguish between 3D Shapes? PLoS ONE 11(2): e0147106.