Visual pattern recognition in Drosophila involves retinotopic matching

HONEYBEES remember the shapes of flowers and are guided by visual landmarks on their foraging trips^1,2. How insects recognize visual patterns is poorly understood. Experiments suggest that they try to match retinotopically the incoming visual pattern with a previously stored memory image²⁷. But bees can be conditioned to individual pattern parameters such as orientation of contours, colour or size^2,811. These and other results are difficult to reconcile with simple template matching. In such investigations, freely moving animals are observed; their behaviour and visual input, therefore, are not well known. Mostly, processing strategies are inferred from stimulus design. We have studied visual pattern recognition with tethered flies (Drosophila melanogaster) in a flight simulator and report here that flies store visual images at, or together with, fixed retinal positions and can retrieve them from there only⁵. Position invariance, an acknowledged property of human pattern recognition, may not exist as a primary mechanism in insects.