@article {Stubbs017756, author = {Alexander L. Stubbs and Christopher W. Stubbs}, title = {Spectral Discrimination in {\textquotedblleft}Color Blind{\textquotedblright} Animals via Chromatic Aberration and Pupil Shape}, elocation-id = {017756}, year = {2015}, doi = {10.1101/017756}, publisher = {Cold Spring Harbor Laboratory}, abstract = {We present a mechanism by which organisms with only a single photoreceptor, that have a monochromatic view of the world, can achieve color discrimination. The combination of an off-axis pupil and the principle of chromatic aberration (where light of different colors focus at different distances behind a lens) can combine to provide {\textquotedblleft}color-blind{\textquotedblright} animals with a way to distinguish colors. As a specific example we constructed a computer model of the visual system of cephalopods, (octopus, squid, and cuttlefish) that have a single unfiltered photoreceptor type. Nevertheless, cephalopods dramatically change color both to produce chromatically-matched camouflage and to signal conspecifics. This presents a paradox {\textendash} an apparent ability to determine color in organisms with a monochromatic visual system {\textendash} that has been a long-standing puzzle. We demonstrate that chromatic blurring dominates the visual acuity in these animals, and we quantitatively show how chromatic aberration can be exploited, especially through non-axial pupils that are characteristic of cephalopods, to obtain spectral information. This mechanism is consistent with the extensive suite of visual/behavioral and physiological data that have been obtained from cephalopod studies, and resolves the apparent paradox of vivid chromatic behaviors in {\textquotedblleft}color-blind{\textquotedblright} animals. Moreover, this proposed mechanism has potential applicability in any organisms with limited photoreceptor complements, such as spiders and dolphins.}, URL = {https://www.biorxiv.org/content/early/2015/10/26/017756}, eprint = {https://www.biorxiv.org/content/early/2015/10/26/017756.full.pdf}, journal = {bioRxiv} }