Cephalopod Eyes and Light Sensing Skin

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A Novel Mechanism for Color Vision: Pupil Shape and Chromatic Aberration Can Provide Spectral Discrimination for Color Blind Organisms.
Alexander L Stubbs, Christopher W Stubbs 2016 (BioRxRv - pre-peer review PDF)
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 color-blind 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, an apparent ability to determine color in organisms with a monochromatic visual system 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 color-blind animals. Moreover, this proposed mechanism has potential applicability in any organisms with limited photoreceptor complements, such as spiders and dolphins.

video briefly explaining this concept.

Full text with images in the Proceedings of the National Academy of Sciences of the United States of America
 
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DWhatley

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This Squid Has Glowing Eyeshadow That Acts Like An Invisibility Cloak
NatGeo Phenomena Ed Yong 2016

... Amanda Holt and Alison Sweeney from the University of Pennsylvania have now reported in the Journal of the Royal Society Interface that a glass squid’s photophore consists of long, skinny cells that are shaped like hockey sticks—they run parallel to the eye, and then take a sharp downward turn. The walls of these cells are lined with reflective proteins that turn them into living optic fibres. They channel the photophore’s light along their length and then downwards, into the ocean’s depths. ...
 

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Camouflage artists, in color
Study proposes explanation for how cephalopods see color, despite black and white vision
HARVARD UNIVERSITY 2016 (summary)

A new study, co-authored by the father-and-son team of Christopher and Alexander Stubbs, suggests that chromatic aberration may explain how cephalopods -- the class of animals that includes squid, octopi and cuttlefish -- can demonstrate such remarkable camouflage abilities despite only being able to see in black and white. The study is described in a July 4, 2016 paper in the Proceedings of the National Academy of Sciences.
 

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Comparative visual ecology of cephalopods from different habitats
Wen-Sung Chung, N. Justin Marshall 2016 (Proceedings of theRoyal Society B full article)

Aside from this methodological advance, the direct MSP evidence presented here indicates that the eight species of coleoid examined all possess a single visual pigment. As a result, unless the unlikely optical solution for colour vision recently suggested by Stubbs & Stubbs [35] can be proved, colour-blindness remains a common feature in all examined coastal coleoids so far.
 

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Pioneering studies on cephalopod’s eye and vision at the Stazione Zoologica Anton Dohrn (1883-1977)
Ariane Dröscher 2016 (full provisional article)

From the late nineteenth century onwards, the phenomena of vision and the anatomy and physiology of the eye of marine animals induced many zoologists, ethologists, physiologists, anatomists, biochemists, and ophthalmologists to travel to the Zoological Station in Naples. Initially, their preferred research objects were fish, but it soon became evident that cephalopods have particular features which make them particularly suited to research. After the first studies, which outlined the anatomical structure of cephalopods’ eyes and optic nerves, the research rapidly shifted to the electrophysiology and biochemistry of vision. In the twentieth century these results were integrated with behavioral tests and training techniques. Between 1909 and 1913 also the well-known debate on color vision between ophthalmologist Carl von Hess and zoologist Karl von Frisch took place in Naples. Largely unknown is that the debate also concerned cephalopods. A comparative historical analysis of these studies shows how different experimental devices, theoretical frameworks, and personal factors gave rise to two diametrically opposing views.
 

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Color Richness in Cephalopod Chromatophores Originating from High Refractive Index Biomolecules
Sean R. Dinneen†, Richard M. OsgoodIII‡, Margaret E. Greenslade†, Leila F. Deravi 2016 (subscription The Journal of Physical Chemistry Letters)
Abstract
jz-2016-02398z_0006.gif

Cephalopods are arguably one of the most photonically sophisticated marine animals, as they can rapidly adapt their dermal color and texture to their surroundings using both structural and pigmentary coloration. Their chromatophore organs facilitate this process, but the molecular mechanism potentiating color change is not well understood. We hypothesize that the pigments, which are localized within nanostructured granules in the chromatophore, enhance the scattering of light within the dermal tissue. To test this, we extracted the phenoxazone-based pigments from the chromatophore and extrapolated their complex refractive index (RI) from experimentally determined real and approximated imaginary portions of the RI. Mie theory was used to calculate the absorbance and scattering cross sections (cm2/particle) across a broad diameter range at λ = 589 nm. We observed that the pigments were more likely to scatter attenuated light than absorb it and that these characteristics may contribute to the color richness of cephalopods.
 

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Testing the Optomotor Response in Sepia bandensis
Lauren Thompson 2017 Honors Thesis Georgia Southern University (full PDF)
ABSTRACT Cephalopods (octopus, squid, and cuttlefish) have commonly been used as models to test visual function and camouflage due to their similarity in eye morphology with humans and because of their readily observable changes in body color in response to visual stimuli. Most studies have used a single species, Sepia officinalis, to make broad conclusions about camouflage and vision. However, these generalizations may not be applicable to all species. Here, I have examined visual function of the dwarf cuttlefish (Sepia bandensis), which differs from S. officinalis in habitat, geographic range, and size. Using the optomotor response, I quantified the minimum separable angle (MSA) of resolution, a behavioral measure of visual acuity, by recording cuttlefish movement in response to rotating black and white stripes of decreasing stripe width. The threshold of visual acuity for these experiments was a stripe width of 5mm and a MSA of 3.76°. These results indicate that S. bandensis has poorer visual acuity than S. officinalis (MSA 0.57°), and therefore, may be less able to resolve fine details in the environment. The ability to perceive these fine details enables animals to navigate, forage, and communicate with conspecifics. Future work should examine the behavioral ecology of S. bandensis to understand the biological and physical environmental context in which visual cues are used by this species.
 

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Visual ecology and the development of visually guided behavior in the cuttlefish
Anne-Sophie DARMAILLACQ, Nawel Mezrai, Caitlin E. O'Brien, Ludovic Dickel 2017(subscription Frontiers inf Physiology)

Cuttlefish are highly visual animals, a fact reflected in the large size of their eyes and visual-processing centers of their brain. Adults detect their prey visually, navigate using visual cues such as landmarks or the e-vector of polarized light and display intense visual patterns during mating and agonistic encounters. Although much is known about the visual system in adult cuttlefish, few studies have investigated its development and that of visually-guided behavior in juveniles. This review summarizes the results of studies of visual development in embryos and young juveniles. The visual system is the last to develop, as in vertebrates, and is functional before hatching. Indeed, embryonic exposure to prey, shelters or complex background alters postembryonic behavior. Visual acuity and lateralization, and polarization sensitivity improve throughout the first months after hatching. The production of body patterning in juveniles is not the simple stimulus-response process commonly presented in the literature. Rather, it likely requires the complex integration of visual information, and is subject to inter-individual differences. Though the focus of this review is vision in cuttlefish, it is important to note that other senses, particularly sensitivity to vibration and to waterborne chemical signals, also play a role in behavior. Considering the multimodal sensory dimensions of natural stimuli and their integration and processing by individuals offer new exciting avenues of future inquiry.
 

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Vision in Cephalopods Frontiers research collection 2018 Ebook available

This Research Topic is aimed to focus on current advances in the knowledge of cephalopod vision. It is designed to facilitate merging questions, approaches and data available through the work of different researchers working on different aspects of cephalopod vision. Thus the research topic will create mutual awareness, and will facilitate the growth of a field of research with a long tradition - cephalopod vision, visual perception and cognition as well as the mechanisms of camouflage.
 

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