Browsing by Subject "polarization sensitivity"
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Item The molecular basis of mechanisms underlying polarization vision(The Royal Society, 2011-03-12) Roberts, Nicholas W.; Porter, Megan L.; Cronin, Thomas W.The underlying mechanisms of polarization sensitivity (PS) have long remained elusive. For rhabdomeric photoreceptors, questions remain over the high levels of PS measured experimentally. In ciliary photoreceptors, and specifically cones, little direct evidence supports any type of mechanism. In order to promote a greater interest in these fundamental aspects of polarization vision, we examined a varied collection of studies linking membrane biochemistry, protein–protein interactions, molecular ordering and membrane phase behaviour. While initially these studies may seem unrelated to polarization vision, a common narrative emerges. A surprising amount of evidence exists demonstrating the importance of protein–protein interactions in both rhabdomeric and ciliary photoreceptors, indicating the possible long-range ordering of the opsin protein for increased PS. Moreover, we extend this direction by considering how such protein paracrystalline organization arises in all cell types from controlled membrane phase behaviour and propose a universal pathway for PS to occur in both rhabdomeric and cone photoreceptors.Item New directions in the detection of polarized light(The Royal Society, 2011-03-12) Marshall, Justin; Cronin, Thomas; Wehling, Martin F.Item Polarization patterns of the twilight sky(SPIE, 2005-08-18) Cronin, Thomas W.; Warrant, Eric J.; Greiner, BirgitAlthough natural light sources produce depolarized light, patterns of partially linearly polarized light appear in the sky due to scattering from air molecules, dust, and aerosols. Many animals, including bees and ants, orient themselves to patterns of polarization that are present in daytime skies, when the intensity is high and skylight polarization is strong and predictable. The halicitid bee Megalopta genalis inhabits rainforests in Central America. Unlike typical bees, it forages before sunrise and after sunset, when light intensities under the forest canopy are very low, and must find its way to food sources and return to its nest in visually challenging circumstances. An important cue for the orientation could be patterns of polarization in the twilight sky. Therefore, we used a calibrated digital camera to image skylight polarization in an overhead patch of sky, 87.6° across, before dawn on Barro Colorado Island in Panama, where the bees are found. We simultaneously measured the spectral properties of polarized light in a cloudless patch of sky 15° across centered on the zenith. We also performed full-sky imaging of polarization before dawn and after dusk on Lizard Island in Australia, another tropical island. During twilight, celestial polarized light occurs in a wide band stretching perpendicular to the location of the hidden sun and reaching typical degrees of polarization near 80% at wavelengths >600 nm. This pattern appears about 45 minutes before local sunrise or disappears 45 minutes after local sunset (about 20 minutes after the onset of astronomical twilight at dawn, or before its end at dusk) and extends with little change through the entire twilight period. Such a strong and reliable orientation cue could be used for flight orientation by any animal with polarization sensitivity that navigates during twilight.Item Polarization signals in the marine environment(SPIE, 2003-12-12) Cronin, Thomas W.; Shashar, Nadav; Caldwell, Roy L.; Marshall, Justin; Cheroske, Alexander G.; Chiou, Tsyr-HueiAlthough natural light sources produce depolarized light, partially linearly polarized light is naturally abundant in the scenes animals view, being produced by scattering in air or water or by reflection from shiny surfaces. Many species of animals are sensitive to light's polarization, and use this sensitivity to orient themselves using polarization patterns in the atmosphere or underwater. A few animal species have been shown to take this polarization sensitivity to another level of sophistication, seeing the world as a polarization image, analogous to the color images humans and other animals view. This sensory capacity has been incorporated into biological signals by a smaller assortment of species, who use patterns of polarization on their bodies to communicate with conspecific animals. In other words, they use polarization patterns for tasks similar to those for which other animals use biologically produced color patterns. Polarization signals are particularly useful in marine environments, where the spectrum of incident light is variable and unpredictable. Here, cephalopod mollusks (octopuses, squids, and cuttlefish) and stomatopod crustaceans (mantis shrimps) have developed striking patterns of polarization used in communication.Item Polarization Vision and Its Role in Biological Signaling(Oxford University Press, 2003-08-01) Cronin, Thomas W.; Shashar, Nadav; Caldwell, Roy L.; Marshall, Justin; Cheroske, Alexander G.; Chiou, Tsyr-HueiVisual pigments, the molecules in photoreceptors that initiate the process of vision, are inherently dichroic, differentially absorbing light according to its axis of polarization. Many animals have taken advantage of this property to build receptor systems capable of analyzing the polarization of incoming light, as polarized light is abundant in natural scenes (commonly being produced by scattering or reflection). Such polarization sensitivity has long been associated with behavioral tasks like orientation or navigation. However, only recently have we become aware that it can be incorporated into a high-level visual perception akin to color vision, permitting segmentation of a viewed scene into regions that differ in their polarization. By analogy to color vision, we call this capacity polarization vision. It is apparently used for tasks like those that color vision specializes in: contrast enhancement, camouflage breaking, object recognition, and signal detection and discrimination. While color is very useful in terrestrial or shallow-water environments, it is an unreliable cue deeper in water due to the spectral modification of light as it travels through water of various depths or of varying optical quality. Here, polarization vision has special utility and consequently has evolved in numerous marine species, as well as at least one terrestrial animal. In this review, we consider recent findings concerning polarization vision and its significance in biological signaling.Item Transmission of linearly polarized light in seawater: implications for polarization signaling(The Company of Biologists Ltd, 2004-07-12) Shashar, Nadav; Sabbah, Shai; Cronin, Thomas W.Partially linearly polarized light is abundant in the oceans. The natural light field is partially polarized throughout the photic range, and some objects and animals produce a polarization pattern of their own. Many polarization-sensitive marine animals take advantage of the polarization information, using it for tasks ranging from navigation and finding food to communication. In such tasks, the distance to which the polarization information propagates is of great importance. Using newly designed polarization sensors, we measured the changes in linear polarization underwater as a function of distance from a standard target. In the relatively clear waters surrounding coral reefs, partial (%) polarization decreased exponentially as a function of distance from the target, resulting in a 50% reduction of partial polarization at a distance of 1.25–3·m, depending on water quality. Based on these measurements, we predict that polarization sensitivity will be most useful for short-range (in the order of meters) visual tasks in water and less so for detecting objects, signals, or structures from far away. Navigation and body orientation based on the celestial polarization pattern are predicted to be limited to shallow waters as well, while navigation based on the solar position is possible through a deeper range.