TUTHILL, J.C.*; JOHNSEN, S.; Swarthmore College; Duke University: Polarization vision in crayfish enhances motion detection

Many animals can discriminate between two stimuli based solely on differences in the orientation of polarized light. Although this capacity has been demonstrated in some vertebrates, the most common examples are invertebrates such as cephalopods, insects, and crustaceans. The functions of polarization sensitivity are as diverse as the organisms that use it, including such tasks as orientation, navigation, inter-specific communication, camouflage-breaking, and possibly contrast enhancement and motion detection. We tested the hypothesis that polarization vision can enhance visual sensitivity to motion by examining the escape response of crayfish reacting to a visual threat. A transparent, polarization-active model was advanced toward individual crayfish isolated in a chamber illuminated by either partially polarized or depolarized light. Under partially linearly polarized light conditions comparable to an aquatic environment, 88% of crayfish (n=40) responded to the threat by meeting a predetermined response criterion. Under depolarized illumination of identical intensity, only 24% responded to the same visual cue (n=40). While the potential for polarization sensitivity has been shown in neurophysiological and structural studies of the crayfish visual system, our results provide the first behavioral evidence for polarization vision in crayfish, and the first demonstration of polarization vision as a tool for motion detection. Polarization discrimination may serve a purpose analogous to color vision, improving detection and recognition of moving objects in a partially polarized environment.