High-resolution polarisation vision in a cuttlefish

Figure 1. High-resolution polarisation vision in Sepia plangon improves image contrast. (A) S. plangon responded to looming stimuli that differed in angle of polarisation from the background with an innate deimatic diplay (brightening of body colour). Left portion = pre-stimulus; right portion = post stimulus. (B) Normalized response strength (see Supplemental Information for further details) decreased as the difference between the e-vector angle of the stimulus and background decreased (solid line). The minimum e-vector discrimination was 1.05° (one-sided paired t-test between normalized level of response and a baseline level of body colour change one and a half seconds prior to stimulus onset). A Benjamini-Hochberg correction for repeated measures was used (see Supplemental Information for further details). Error bars represent mean +/1 S.E. Black numbers over error bars indicate the number of individuals tested. Red numbers below error bars are p-values. (C-F) Imaging polarimetry of an unidentified penaeid shrimp (C and D) and a small perciform fish, black bream (Acanthopagrus australis) (E and F). The reflections from both animals appear to match the angle of the background e-vector closely when the images are processed with standard, low-resolution imaging polarimetry (C and E). However, more information is available in the polarisation dimension when using high-resolution analysis/sensitivity (D and F), where the false colour palette (colour wheel insert in C and E indicating e-vector angle) is compressed into a 45° range (See Supplemental Information for further details). As evident from C and E almost all the polarisation information falls within this angular range. These images model polarisation information (which humans are unable to detect) and convert it to colour, but it is important to note that they are only a model that highlights the information available at higher resolutions and are not an accurate representation of what cuttlefish see. High-resolution polarisation vision in a cuttlefish