RT Journal Article SR Electronic T1 Pupil Shape and Chromatic Aberration Can Provide Spectral Discrimination for “Color Blind” Animals JF bioRxiv FD Cold Spring Harbor Laboratory SP 017756 DO 10.1101/017756 A1 Alexander L. Stubbs A1 Christopher W. Stubbs YR 2015 UL http://biorxiv.org/content/early/2015/04/09/017756.abstract AB The only known mechanism for color vision requires spectrally diverse photoreceptor types (1). However color vision comes at a cost: a reduction in the signal to noise ratio in low light conditions and angular resolution in each spectral channel. Coleoid cephalopods (octopus, squid, cuttlefish) have a single photoreceptor type (2,3,4) and lack the ability to determine color by comparing detected photon intensity across multiple spectral channels. Nevertheless, cephalopods produce vividly colorful mating displays and use adaptive camouflage to accurately match the color of their natural surroundings. This presents a paradox - behaviors that imply an ability to determine color in creatures with a monochromatic visual system - that has long puzzled vision scientists and biologists (5,6,7). Here we propose a novel mechanism for spectral discrimination: the exploitation of chromatic aberration (the wavelength-dependence of focal length) by organisms with a single photoreceptor type. Through numerical modeling we show how chromatic aberration can yield useful chromatic information via the dependence of image acuity on accommodation. The peculiar off-axis slit and annular pupil shapes in these animals enhance this chromatic signature. This picture is consistent with existing data on cephalopod behavior and retinal morphology, and may have broader applicability in other species.