One of the remarkable properties of the eyes of some animals is the ability to detect the special physical property of polarization of light. Polarized light is particularly important underwater, and there is circumstantial evidence that some marine animals use polarized light to detect environmental cues. Many cephalopod molluscs (cuttlefish, squid, and allies) have highly developed visual systems. Cuttlefish not only may use polarized light cues for wide-field environmental cues, but may use it also for displays of patterns on the body, as they do with color patterns for camouflage and social displays. This project combines photometery (using a new underwater imaging polarimeter), electrophysiology, microscopy, and ethological studies of cuttlefish as an excellent model system for exploring how polarized light might be an important environmental and behavioral visual stimulus. Results will be important beyond visual neuroscience, for a better understanding of important marine organisms, and for potential applications in aquaculture and in the design of optical sensors and machine vision.