The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Nathan S Hart - One of the best experts on this subject based on the ideXlab platform.
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visual pigments in a palaeognath bird the emu dromaius novaehollandiae implications for Spectral Sensitivity and the origin of ultraviolet vision
Proceedings of The Royal Society B: Biological Sciences, 2016Co-Authors: Nathan S Hart, Jessica K Mountford, Wayne I L Davies, Shaun P Collin, David M HuntAbstract:A comprehensive description of the Spectral characteristics of retinal photoreceptors in palaeognaths is lacking. Moreover, controversy exists with respect to the Spectral Sensitivity of the short-wavelength-sensitive-1 (SWS1) opsin-based visual pigment expressed in one type of single cone: previous microspectrophotometric (MSP) measurements in the ostrich (Struthio camelus) suggested a violet-sensitive (VS) SWS1 pigment, but all palaeognath SWS1 opsin sequences obtained to date (including the ostrich) imply that the visual pigment is ultraviolet-sensitive (UVS). In this study, MSP was used to measure the Spectral properties of visual pigments and oil droplets in the retinal photoreceptors of the emu (Dromaius novaehollandiae). Results show that the emu resembles most other bird species in possessing four Spectrally distinct single cones, as well as double cones and rods. Four cone and a single rod opsin are expressed, each an orthologue of a previously identified pigment. The SWS1 pigment is clearly UVS (wavelength of maximum absorbance [λmax] = 376 nm), with key tuning sites (Phe86 and Cys90) consistent with other vertebrate UVS SWS1 pigments. Palaeognaths would appear, therefore, to have UVS SWS1 pigments. As they are considered to be basal in avian evolution, this suggests that UVS is the most likely ancestral state for birds. The functional significance of a dedicated UVS cone type in the emu is discussed.
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spatial resolving power and Spectral Sensitivity of the saltwater crocodile crocodylus porosus and the freshwater crocodile crocodylus johnstoni
The Journal of Experimental Biology, 2016Co-Authors: Nicolas Nagloo, Nathan S Hart, Shaun P Collin, Jan M HemmiAbstract:ABSTRACT Crocodilians are apex amphibious predators that occupy a range of tropical habitats. In this study, we examined whether their semi-aquatic lifestyle and ambush hunting mode are reflected in specific adaptations in the peripheral visual system. Design-based stereology and microspectrophotometry were used to assess spatial resolving power and Spectral Sensitivity of saltwater (Crocodylus porosus) and freshwater crocodiles (Crocodylus johnstoni). Both species possess a foveal streak that spans the naso-temporal axis and mediates high spatial acuity across the central visual field. The saltwater crocodile and freshwater crocodile have a peak spatial resolving power of 8.8 and 8.0 cycles deg−1, respectively. Measurement of the outer segment dimensions and Spectral absorbance revealed five distinct photoreceptor types consisting of three single cones, one twin cone and a rod. The three single cones (saltwater/freshwater crocodile) are violet (424/426 nm λmax), green (502/510 nm λmax) and red (546/554 nm λmax) sensitive, indicating the potential for trichromatic colour vision. The visual pigments of both members of the twin cones have the same λmax as the red-sensitive single cone and the rod has a λmax at 503/510 nm (saltwater/freshwater). The λmax values of all types of visual pigment occur at longer wavelengths in the freshwater crocodile compared with the saltwater crocodile. Given that there is a greater abundance of long wavelength light in freshwater compared with a saltwater environment, the photoreceptors would be more effective at detecting light in their respective habitats. This suggests that the visual systems of both species are adapted to the photic conditions of their respective ecological niche.
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visual pigments cone oil droplets ocular media and predicted Spectral Sensitivity in the domestic turkey meleagris gallopavo
Vision Research, 1999Co-Authors: Nathan S Hart, J C Partridge, Innes C CuthillAbstract:A microspectrophotometric survey conducted on the retinal photoreceptors of the domestic turkey (Meleagris gallopavo) revealed the presence of five different types of vitamin A1-based visual pigment (rhodopsin) in seven different types of photoreceptor. A single class of rod contained a medium wavelength-sensitive visual pigment (wavelength of maximum absorbance, λmax, 504 nm). Four different types of single cone contained visual pigment maximally sensitive to wavelengths in either the long (LWS, λmax 564 nm), medium (MWS, λmax 505 nm), short (SWS, λmax 460 nm) or violet (VS, λmax 420 nm) Spectral ranges. The LWS, MWS and SWS single cones contained pigmented oil droplets with cut-off wavelengths (λcut) at 514, 490 and 437 nm, respectively. The VS single cone contained a transparent oil droplet which displayed no significant absorbance above 330 nm. A single class of double cone was also identified, both the principal and accessory members of which contained the LWS cone visual pigment. The principal member contained an oil droplet with a λcut at 436 nm. No oil droplet was observed in the accessory member. The use of a glycerol-based cell mountant, which reduced wavelength dependent measurement artefacts in the microspectrophotometric measurements, is described. Predictions of cone effective Spectral Sensitivity, incorporating measurements of the Spectral transmission of the ocular media, suggest that turkeys have considerable Sensitivity to wavelengths in the ultraviolet-A (UV-A, 315–400 nm) Spectral range. This has implications for both the visual ecology of wild birds and the welfare of intensively farmed individuals.
Ellis R. Loew - One of the best experts on this subject based on the ideXlab platform.
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The importance of ultraviolet and near-infrared Sensitivity for visual discrimination in two species of lacertid lizards
Journal of Experimental Biology, 2015Co-Authors: Melissa Martin, Sandrine Meylan, Jean-françois Le Galliard, Ellis R. LoewAbstract:Male and female Lacertid lizards often display conspicuous coloration that is involved in intraspecific communication. However, visual systems of Lacertidae have rarely been studied and the Spectral Sensitivity of their retinal photoreceptors remains unknown. Here, we characterise the Spectral Sensitivity of two Lacertid species from contrasting habitats: the wall lizard Podarcis muralis and the common lizard Zootoca vivipara. Both species possess a pure-cone retina with one Spectral class of double cones and four Spectral classes of single cones. The two species differ in the Spectral Sensitivity of the LWS cones, the relative abundance of UVS single cones (potentially more abundant in Z. vivipara) and the coloration of oil droplets. Wall lizards have pure vitamin A1-based photopigments, whereas common lizards possess mixed vitamin A1 and A2 photopigments, extending Spectral Sensitivity into the near infrared, which is a rare feature in terrestrial vertebrates. We found that Spectral Sensitivity in the UV and near infrared improves discrimination of small variations in throat coloration among Z. vivipara. Thus, retinal specialisations optimise chromatic resolution in common lizards, indicating that the visual system and visual signals might co-evolve.
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oblique color vision in an open habitat bird Spectral Sensitivity photoreceptor distribution and behavioral implications
The Journal of Experimental Biology, 2012Co-Authors: Bret A Moore, Ellis R. Loew, Patrice Baumhardt, Megan Doppler, Jacquelyn Randolet, Bradley F Blackwell, Travis L Devault, Esteban FernandezjuricicAbstract:Color vision is not uniform across the retina because of differences in photoreceptor density and distribution. Retinal areas with a high density of cone photoreceptors may overlap with those with a high density of ganglion cells, increasing hue discrimination. However, there are some exceptions to this cell distribution pattern, particularly in species with horizontal visual streaks (bands of high ganglion cell density across the retina) that live in open habitats. We studied the Spectral Sensitivity and distribution of cone photoreceptors involved in chromatic and achromatic vision in the Canada goose (Branta canadiensis), which possesses an oblique rather than horizontal visual streak at the ganglion cell layer. Using microspectrophotometry, we found that the Canada goose has a violet-sensitive visual system with four visual pigments with absorbance peaks at 409, 458, 509 and 580 nm. The density of most cones involved in chromatic and achromatic vision peaked along a band across the retina that matched the oblique orientation of the visual streak. With the information on visual Sensitivity, we calculated chromatic and achromatic contrasts of different goose plumage regions. The regions with the highest visual saliency (cheek, crown, neck and upper tail coverts) were the ones involved in visual displays to maintain flock cohesion. The Canada goose oblique visual streak is the retinal center for chromatic and achromatic vision, allowing individuals to sample the sky and the ground simultaneously or the horizon depending on head position. Overall, our results show that the Canada goose visual system has features that make it rather different from that of other vertebrates living in open habitats.
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photopigment Spectral absorbance of lake malawi cichlids
Journal of Fish Biology, 2006Co-Authors: Rebecca Jordan, Karen Kellogg, David V Howe, Francis Juanes, Jay R Stauffer, Ellis R. LoewAbstract:To predict Spectral Sensitivity, microspectrophotometry (MSP) was used to measure absorbance of photoreceptor cells from 15 species of Lake Malaŵi cichlids. Each fish had one rod and at least three cone pigments. UV-sensitive pigments were common, but Spectral Sensitivity did not clearly correlate with feeding mode or habitat.
Thomas Kocher - One of the best experts on this subject based on the ideXlab platform.
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Cone Opsin Genes of African Cichlid Fishes: Tuning Spectral Sensitivity by Differential Gene Expression
Molecular Biology and Evolution, 2001Co-Authors: Karen L. Carleton, Thomas KocherAbstract:Spectral tuning of visual pigments is typically accomplished through changes in opsin amino acid sequence. Within a given opsin class, changes at a few key sites control wavelength specificity. To investigate known differences in the visual pigment Spectral Sensitivity of the Lake Malawi cichlids, Metriaclima zebra (368, 488, and 533 nm) and Dimidiochromis compressiceps (447, 536, and 569 nm), we sequenced cone opsin genes from these species as well as Labeotropheus fuelleborni and Oreochromis niloticus. These cichlids have five distinct classes of cone opsin genes, including two unique SWS-2 genes. Comparisons of the inferred amino acid sequences from the five cone opsin genes of M. zebra, D. compressiceps, and L. fuelleborni show the sequences to be nearly identical. Therefore, evolution of key opsin sites cannot explain the differences in visual pigment sensitivities. Real-time PCR demonstrates that different cichlid species express different subsets of the available cone opsin genes. Metriaclima zebra and L. fuelleborni express a complement of genes which give them UV-shifted visual pigments, while D. compressiceps expresses a different set to produce a red-shifted visual system. Thus, variations in cichlid Spectral Sensitivity have arisen through evolution of gene regulation, rather than through changes in opsin amino acid sequence.
Sabine Susstrunk - One of the best experts on this subject based on the ideXlab platform.
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what is the space of Spectral Sensitivity functions for digital color cameras
Workshop on Applications of Computer Vision, 2013Co-Authors: Jun Jiang, Dengyu Liu, Sabine SusstrunkAbstract:Camera Spectral Sensitivity functions relate scene radiance with captured RGB triplets. They are important for many computer vision tasks that use color information, such as multiSpectral imaging, color rendering, and color constancy. In this paper, we aim to explore the space of Spectral Sensitivity functions for digital color cameras. After collecting a database of 28 cameras covering a variety of types, we find this space convex and two-dimensional. Based on this statistical model, we propose two methods to recover camera Spectral sensitivities using regular reflective color targets (e.g., color checker) from a single image with and without knowing the illumination. We show the proposed model is more accurate and robust for estimating camera Spectral sensitivities than other basis functions. We also show two applications for the recovery of camera Spectral sensitivities - simulation of color rendering for cameras and computational color constancy.
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optimum Spectral Sensitivity functions for single sensor color imaging
Proceedings of SPIE, 2012Co-Authors: Zahra Sadeghipoor, Sabine SusstrunkAbstract:A cost-effective and convenient approach for color imaging is to use a single sensor and mount a color filter array (CFA) in front of it, such that at each spatial position the scene information in only one color channel is captured. To estimate the missing colors at each pixel, a demosaicing algorithm is applied to the CFA samples. Besides the filter arrangement and the demosaicing method, the Spectral Sensitivity functions of the CFA filters considerably affect the quality of the demosaiced image. In this paper, we propose an algorithm to compute the optimum Spectral sensitivities of filters in the single sensor imager. The proposed algorithm solves a constrained optimization problem to find optimum Spectral sensitivities and the corresponding linear demosaicing method. An important constraint for this problem is the smoothness of Spectral sensitivities, which is imposed by modeling these functions as a linear combination of several smooth kernels. Simulation results verify the effectiveness of the proposed algorithm in finding optimal Spectral Sensitivity functions, which outperform measured camera Sensitivity functions.
Z Yu - One of the best experts on this subject based on the ideXlab platform.
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extraordinarily high Spectral Sensitivity in refractive index sensors using multiple optical modes
Conference on Lasers and Electro-Optics, 2012Co-Authors: Z YuAbstract:We show that high Spectral Sensitivity in surface plasmon resonance sensor is due to the multi-mode nature of the sensing scheme. Multi-mode sensing can be applied to dielectric systems to achieve similar extraordinary Spectral Sensitivity.
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extraordinarily high Spectral Sensitivity in refractive index sensors using multiple optical modes
Optics Express, 2011Co-Authors: Z YuAbstract:The extraordinary Spectral Sensitivity of surface plasmon resonance (SPR) sensors is commonly attributed to the modal overlap or unique dispersion of surface plasmons. In contrast to this belief, we show that such high Sensitivity is due to the multi-mode nature of the sensing scheme. This concept of multi-mode sensing can be applied to dielectric systems as well in order to achieve similar extraordinary Spectral Sensitivity. We also show that there is a fundamental constraint between the Spectral Sensitivity and quality factor in such multi-mode sensing approach.
