Model Of Color Vision Research Articles

Analysis of Hue Circle Perception of Congenital Red-green Congenital Color Deficiencies Based on Color Vision Model

To investigate individual property of internal color representation of congenital red-green color-deficient observers (CDOs) and color-normal observers (CNOs) precisely, difference scaling experiment using pairs of primary colors was carried out for protans, deutans, and normal trichromats, and the results were analyzed using multi-dimensional Scaling (MDS). MDS configuration of CNOs showed circular shape similar to hue circle, whereas that of CNO showed large individual differences from circular to U- shape. Distortion index, DI, is proposed to express the shape variation of MDS configuration. All color chips were plotted in the color vision space, (L, r/g, y/b), and the MDS using a non-linear conversion from the distance in the color vision space to perceptual difference scaling was successful to obtain U-shape configuration that reflects internal color representation of CDOs.

The spectral sensitivity of Drosophila photoreceptors

Drosophila melanogaster has long been a popular model insect species, due in large part to the availability of genetic tools and is fast becoming the model for insect colour vision. Key to understanding colour reception in Drosophila is in-depth knowledge of spectral inputs and downstream neural processing. While recent studies have sparked renewed interest in colour processing in Drosophila, photoreceptor spectral sensitivity measurements have yet to be carried out in vivo. We have fully characterised the spectral input to the motion and colour vision pathways, and directly measured the effects of spectral modulating factors, screening pigment density and carotenoid-based ocular pigments. All receptor sensitivities had significant shifts in spectral sensitivity compared to previous measurements. Notably, the spectral range of the Rh6 visual pigment is substantially broadened and its peak sensitivity is shifted by 92 nm from 508 to 600 nm. We show that this deviation can be explained by transmission of long wavelengths through the red screening pigment and by the presence of the blue-absorbing filter in the R7y receptors. Further, we tested direct interactions between inner and outer photoreceptors using selective recovery of activity in photoreceptor pairs.

Carotenoid‐based plumage colour saturation increases with temperature in Australian passerines

AbstractAimBirds are often coloured yellow, olive, orange or red by carotenoids, which are plant pigments that are ingested with food. Here we test whether there are consistent patterns of intraspecific geographic variation in male carotenoid‐based plumage coloration linked to latitude, temperature, precipitation and primary productivity. It has been suggested that patterns of geographic variation should be different for yellow, compared to the metabolically derived red carotenoid‐based coloration, but this has not been tested.LocationAustralia.TaxaForty‐nine randomly selected species of Australian passerine birds (Passeriformes), 30 with yellow and 19 with red carotenoid‐based plumage coloration.MethodsCarotenoid‐based plumage patches of male museum specimens were measured using reflectance spectrometry, and spectra analysed using models of avian colour vision. For each species, we used linear models to determine whether geographic variation in carotenoid‐based colour correlated with latitude, temperature, precipitation or primary productivity. To determine whether effects are consistent across species, we used phylogenetic meta‐analyses.ResultsAlthough spatial environmental effects on carotenoid‐based plumage coloration varied across species, overall, species tended to have more saturated carotenoid‐based coloration at lower latitudes, and warmer regions. These effects applied mainly to resident species (as opposed to migratory or nomadic) and were stronger for red compared to yellow carotenoid‐based colours. We found no consistent effects of precipitation or primary productivity.Main conclusionsGeographic variation in male carotenoid‐based plumage coloration of Australian passerines is unlikely to be caused by variation in plant productivity (the ultimate source of carotenoids), and may be better explained by latitudinal gradients in the intensity of sexual selection or predation risk. Alternatively, temperature effects on red carotenoid‐based coloration may be driven by the hypothesized link between carotenoid and cellular metabolism. Latitudinal and temperature effects have the potential to generate perceivable differences in coloration across realistic spatial scales, contributing to divergence in visual signals.

Zebrafish Retinal Ganglion Cells Asymmetrically Encode Spectral and Temporal Information across Visual Space

SummaryIn vertebrate vision, the tetrachromatic larval zebrafish permits non-invasive monitoring and manipulating of neural activity across the nervous system in vivo during ongoing behavior. However, despite a perhaps unparalleled understanding of links between zebrafish brain circuits and visual behaviors, comparatively little is known about what their eyes send to the brain via retinal ganglion cells (RGCs). Major gaps in knowledge include any information on spectral coding and information on potentially critical variations in RGC properties across the retinal surface corresponding with asymmetries in the statistics of natural visual space and behavioral demands. Here, we use in vivo two-photon imaging during hyperspectral visual stimulation as well as photolabeling of RGCs to provide a functional and anatomical census of RGCs in larval zebrafish. We find that RGCs’ functional and structural properties differ across the eye and include a notable population of UV-responsive On-sustained RGCs that are only found in the acute zone, likely to support visual prey capture of UV-bright zooplankton. Next, approximately half of RGCs display diverse forms of color opponency, including many that are driven by a pervasive and slow blue-Off system—far in excess of what would be required to satisfy traditional models of color vision. In addition, most information on spectral contrast was intermixed with temporal information. Taken together, our results suggest that zebrafish RGCs send a diverse and highly regionalized time-color code to the brain.

Red flowers differ in shades between pollination systems and across continents.

Background and AimsFloral colour is a primary signal in plant–pollinator interactions. The association between red flowers and bird pollination is well known, explained by the ‘bee avoidance’ and ‘bird attraction’ hypotheses. Nevertheless, the relative importance of these two hypotheses has rarely been investigated on a large scale, even in terms of colour perception per se.MethodsWe collected reflectance spectra for 130 red flower species from different continents and ascertained their pollination systems. The spectra were analysed using colour vision models for bees and (three types of) birds, to estimate colour perception by these pollinators. The differences in colour conspicuousness (chromatic and achromatic contrast, purity) and in spectral properties between pollination systems and across continents were analysed.Key ResultsCompared with other floral colours, red flowers are very conspicuous to birds and much less conspicuous to bees. The red flowers pollinated by bees and by birds are more conspicuous to their respective pollinators. Compared with the bird flowers in the Old World, the New World ones are less conspicuous to bees and may be more conspicuous not only to violet-sensitive but also to ultraviolet-sensitive birds. These differences can be explained by the different properties of the secondary reflectance peak (SP). SP intensity is higher in red flowers pollinated by bees than those pollinated by birds (especially New World bird flowers). A transition from high SP to low SP in red flowers can induce chromatic contrast changes, with a greater effect on reducing attraction to bees than enhancing attraction to birds.ConclusionsShades of red flowers differ between pollination systems. Moreover, red bird flowers are more specialized in the New World than in the Old World. The evolution towards colour specialization is more likely to result in higher efficiency of bee avoidance than bird attraction

What the Zebrafish's Eye Tells the Zebrafish's Brain: Retinal Ganglion Cells for Prey Capture and Colour Vision

In vertebrate vision, the tetrachromatic larval zebrafish permits non-invasive monitoring and manipulating of neural activity across the nervous system in vivo during ongoing behaviour. However, despite a perhaps unparalleled understanding of links between zebrafish brain circuits and visual behaviours, comparatively little is known about what their eyes send to the brain in the first place via retinal ganglion cells (RGCs). Major gaps in knowledge include any information on spectral coding, and information on potentially critical variations in RGC properties across the retinal surface to acknowledge asymmetries in the statistics of natural visual space and behavioural demands. Here, we use in vivo two photon (2P) imaging during hyperspectral visual stimulation as well as photolabeling of RGCs to provide the first eye-wide functional and anatomical census of RGCs in larval zebrafish. We find that RGCs’ functional and structural properties differ across the eye and include a notable population of UV-responsive On-sustained RGCs that are only found in the acute zone, likely to support visual prey capture of UV-bright zooplankton. Next, approximately half of RGCs display diverse forms of colour opponency - long in excess of what would be required to satisfy traditional models of colour vision. However, most information on spectral contrast was intermixed with temporal information. To consolidate this series of unexpected findings, we propose that zebrafish may use a novel “dual-achromatic” strategy segregated by a spectrally intermediate background subtraction system. Specifically, our data is consistent with a model where traditional achromatic image-forming vision is mainly driven by long-wavelength sensitive circuits, while in parallel UV-sensitive circuits serve a second achromatic system of foreground-vision that serves prey capture and, potentially, predator evasion.

The Verriest Lecture: Adventures in blue and yellow.

Conventional models of color vision assume that blue and yellow (along with red and green) are the fundamental building blocks of color appearance, yet how these hues are represented in the brain and whether and why they might be special are questions that remain shrouded in mystery. Many studies have explored the visual encoding of color categories, from the statistics of the environment to neural processing to perceptual experience. Blue and yellow are tied to salient features of the natural color world, and these features have likely shaped several important aspects of color vision. However, it remains less certain that these dimensions are encoded as primary or "unique" in the visual representation of color. There are also striking differences between blue and yellow percepts that may reflect high-level inferences about the world, specifically about the colors of light and surfaces. Moreover, while the stimuli labeled as blue or yellow or other basic categories show a remarkable degree of constancy within the observer, they all vary independently of one another across observers. This pattern of variation again suggests that blue and yellow and red and green are not a primary or unitary dimension of color appearance, and instead suggests a representation in which different hues reflect qualitatively different categories rather than quantitative differences within an underlying low-dimensional "color space."

Coupled Retinex

Retinex is a colour vision model introduced by Land more than 40 years ago. Since then, it has also been widely and successfully used for image enhancement. However, Retinex often introduces colour and halo artefacts. Artefacts are a necessary consequence of the per channel color processing and the lack of any strong control for controlling the locality of the processing (halos are very local errors). In this paper we relate an input to the corresponding output processed retinex image by using a single shading term which is both spatially varying and smooth and a global colour shift. This coupling dramatically reduces common Retinex artefacts. Coupled Retinex is strongly preferred in preference tests.

Horse vision and obstacle visibility in horseracing

Visual information is key to how many animals interact with their environment, and much research has investigated how animals respond to colour and brightness information in the natural world. Understanding the visibility of features in anthropogenic environments, and how animals respond to these, is also important, not least for the welfare and safety of animals and the humans they co-exist with, but has received comparatively less attention. One area where this is particularly pertinent is animal sports such as horseracing. Here there is a need to understand how horses see and respond to obstacles, predominantly fences and hurdles, as this has implications for horse and rider safety, however obstacle appearance is currently designed to human perception. Using models of horse colour and luminance (perceived lightness) vision, we analysed the contrast of traditional orange markers currently used on fences from 11 UK racecourses, and compared this to potential alternative colours, while also investigating the effect of light and weather conditions on contrast. We found that for horses, orange has poor visibility and contrast against most surroundings. In comparison, yellow, blue, and white are more conspicuous, with the degree of relative contrast varying with vegetation or background type. Results were mostly consistent under different weather conditions and time of day, except for comparisons with the foreground turf in shade. We then tested the jump responses of racehorses to fences with orange, fluorescent yellow, bright blue, or white takeoff boards and midrails. Fence colour influenced both the angle of the jump and the distances jumped. Bright blue produced a larger angle of takeoff, and jumps over fluorescent yellow fences had shorter landing distances compared to orange, with bright blue fences driving a similar but non-significant trend. White was the only colour that influenced takeoff distances, with horses jumping over white fences having a larger takeoff distance. Overall, our results show that current obstacle coloration does not maximise contrast for horse vision, and that alternative colours may improve visibility and alter behavioural responses, with the ultimate goal of improving safety and welfare.

Reconciling Color Vision Models With Midget Ganglion Cell Receptive Fields.

Midget retinal ganglion cells (RGCs) make up the majority of foveal RGCs in the primate retina. The receptive fields of midget RGCs exhibit both spectral and spatial opponency and are implicated in both color and achromatic form vision, yet the exact mechanisms linking their responses to visual perception remain unclear. Efforts to develop color vision models that accurately predict all the features of human color and form vision based on midget RGCs provide a case study connecting experimental and theoretical neuroscience, drawing on diverse research areas such as anatomy, physiology, psychophysics, and computer vision. Recent technological advances have allowed researchers to test some predictions of color vision models in new and precise ways, producing results that challenge traditional views. Here, we review the progress in developing models of color-coding receptive fields that are consistent with human psychophysics, the biology of the primate visual system and the response properties of midget RGCs.

Floral colour structure in two Australian herbaceous communities: it depends on who is looking.

Pollinator-mediated interactions between plant species may affect the composition of angiosperm communities. Floral colour signals should play a role in these interactions, but the role will arise from the visual perceptions and behavioural responses of multiple pollinators. Recent advances in the visual sciences can be used to inform our understanding of these perceptions and responses. We outline the application of appropriate visual principles to the analysis of the annual cycle of floral colour structure in two Australian herbaceous communities. We used spectrographic measurements of petal reflectance to determine the location of flowers in a model of hymenopteran colour vision. These representations of colour perception were then translated to a behaviourally relevant metric of colour differences using empirically calibrated colour discrimination functions for four hymenopteran species. We then analysed the pattern of colour similarity in terms of this metric in samples of co-flowering plants over the course of a year. We used the same method to analyse the annual pattern of phylogenetic relatedness of co-flowering plants in order to compare colour structure and phylogenetic structure. Co-flowering communities at any given date seldom had colour assemblages significantly different from random. Non-random structure, both dispersion and clustering, occurred occasionally, but depended on which bee observer is considered. The degree of colour similarity was unrelated to phylogenetic similarity within a co-flowering community. Perceived floral colour structure varied with the sensory capabilities of the observer. The lack of colour structure at most sample dates, particularly the rarity of strong dispersion, suggests that plants do not use chromatic signals primarily to enable bees to discriminate between co-flowering species. It is more likely that colours make plants detectable in a complex landscape.

Discrete or indiscrete? Redefining the colour polymorphism of the land snail Cepaea nemoralis

Biologists have long tried to describe and name the different phenotypes that make up the shell polymorphism of the land snail Cepaea nemoralis. Traditionally, the view is that the ground colour of the shell is one of a few major colour classes, either yellow, pink or brown, but in practise it is frequently difficult to distinguish the colours, and define different shades of the same colour. To understand whether colour variation is in reality continuous, and to investigate how the variation may be perceived by an avian predator, we applied psychophysical models of colour vision to shell reflectance measures. We found that both achromatic and chromatic variation are indiscrete in Cepaea nemoralis, being continuously distributed over many perceptual units. Nonetheless, clustering analysis based on the density of the distribution did reveal three groups, roughly corresponding to human-perceived yellow, pink and brown shells. We also found large-scale geographic variation in the frequency of these groups across Europe, and some covariance between shell colour and banding patterns. Although further studies are necessary, the observation of continuous variation in colour is intriguing because the traditional theory is that the underlying supergene that determines colour has evolved to prevent phenotypes from “dissolving” into continuous trait distributions. The findings thus have significance for understanding the Cepaea polymorphism, and the nature of the selection that acts upon it, as well as more generally highlighting the need to measure colour objectively in other systems.

Colour evolution within orchids depends on whether the pollinator is a bee or a fly.

Orchids are a classic angiosperm model for understanding biotic pollination. We studied orchid species within two species-rich herbaceous communities that are known to have either hymenopteran or dipteran insects as the dominant pollinators, in order to understand how flower colour relates to pollinator visual systems. We analysed features of the floral reflectance spectra that are significant to pollinator visual systems and used models of dipteran and hymenopteran colour vision to characterise the chromatic signals used by fly-pollinated and bee-pollinated orchid species. In contrast to bee-pollinated flowers, fly-pollinated flowers had distinctive points of rapid reflectance change at long wavelengths and a complete absence of such spectral features at short wavelengths. Fly-pollinated flowers also had significantly more restricted loci than bee-pollinated flowers in colour space models of fly and bee vision alike. Globally, bee-pollinated flowers are known to have distinctive, consistent colour signals. Our findings of different signals for fly pollination is consistent with pollinator-mediated selection on orchid species that results from the distinctive features of fly visual systems.

Association between community assemblage of flower colours and pollinator fauna: a comparison between Japanese and New Zealand alpine plant communities.

Flower colour plays a major role in the attraction and decision-making of pollinators. Different functional groups of pollinators tend to prefer different flower colours, and therefor may lead to different flower colour compositions among different communities depending on the visual system of the dominant pollinators. However, few studies have investigated the linkage between pollinator fauna and flower colour composition in natural communities, a theme we explored in the present study. Flower spectral reflectance of 106 Japanese and 96 New Zealand alpine plants in the wavelength range 300-700 nm were measured. The composition of pollinator fauna in the communities and the types of pollinators for each plant species were also investigated. Based on bee and fly colour vision models, as well as a principal components analysis, considering phylogenetic non-independence between plant species, flower colours appeared to vary according to pollinator type rather than geographical region. Consequently, flower colour composition differed between the regions, reflecting the bee/fly mixed pollinator fauna of Japan and the fly-dominant pollinator fauna of New Zealand. According to the bee colour vision model, the majority of the colours of hymenopteran-pollinated flowers appeared to be discriminated by bees. In contrast, many of the colours of dipteran-pollinated flowers would not be discriminated by bees and flies. The results suggest that the differences in flower colour composition between Japanese and New Zealand alpine communities are due to differences in the pollinator fauna in these communities rather than differences in abiotic factors between the geographical regions and the phylogenetic origin of the communities.

Prey and predators perceive orb-web spider conspicuousness differently: evaluating alternative hypotheses for color polymorphism evolution.

Color polymorphisms have been traditionally attributed to apostatic selection. The perception of color depends on the visual system of the observer. Theoretical models predict that differently perceived degrees of conspicuousness by two predator and prey species may cause the evolution of polymorphisms in the presence of anti-apostatic and apostatic selection. The spider Gasteracantha cancriformis (Araneidae) possesses several conspicuous color morphs. In orb-web spiders, the prey attraction hypothesis states that conspicuous colors are prey lures that increase spider foraging success via flower mimicry. Therefore, polymorphism could be maintained if each morph attracted a different prey species (multiple prey hypothesis) and each spider mimicked a different flower color (flower mimicry hypothesis). Conspicuous colors could be a warning signal to predators because of the spider’s hard abdomen and spines. Multiple predators could perceive morphs differently and exert different degrees of selective pressures (multiple predator hypothesis). We explored these 3 hypotheses using reflectance data and color vision modeling to estimate the chromatic and achromatic contrast of G. cancriformis morphs as perceived by several potential prey and predator taxa. Our results revealed that individual taxa perceive the conspicuousness of morphs differently. Therefore, the multiple prey hypothesis and, in part, the multiple predator hypothesis may explain the evolution of color polymorphism in G. cancriformis, even in the presence of anti-apostatic selection. The flower mimicry hypothesis received support by color metrics, but not by color vision models. Other parameters not evaluated by color vision models could also affect the perception of morphs and influence morph survival and polymorphism stability.

Intersexual mimicry and flowering phenology facilitate pollination in a dioecious habitat specialist species, Myristica fatua (Myristicaceae)

Myristica fatua is a dioecious specialist species restricted to the endangered, freshwater Myristica swamp forests in the Western Ghats, India. Earlier studies have alluded to pollination by deception in members of the Myristica genus, and thus we examined the pollination ecology comprising floral biology, flower production, flower visitors, and reproductive success in M. fatua and inferred the potential strategies that could permit such deception in this habitat specialist tree. Male flowers provide pollen rewards for an extended period of time while female flowers are rewardless and both sexes are visited by generalist insects, mainly by honeybees and stingless bees. Bee visits were significantly more frequent and longer on male than on female flowers as bees collected pollen from male flowers. We found that flower production patterns create a preponderance of males compared to females in the swamp populations. Using a model of honeybee color vision, we found the distance between the color loci of male and female flowers and based on minimum visual angle subtended by these flowers, we suggest that the two floral sexes cannot be discriminated by bees. Bees are likely deceived by the perceptual similarity of rewardless female flowers to pollen-offering male flowers and pollination is the consequence of foraging errors made by pollinators that encounter largely male–rarely female flower mosaics as they forage among clump-distributed M. fatua trees in the swamp habitat.

Color vision models: Some simulations, a general n-dimensional model, and the colourvision R package.

The development of color vision models has allowed the appraisal of color vision independent of the human experience. These models are now widely used in ecology and evolution studies. However, in common scenarios of color measurement, color vision models may generate spurious results. Here I present a guide to color vision modeling (Chittka (1992, Journal of Comparative Physiology A, 170, 545) color hexagon, Endler & Mielke (2005, Journal Of The Linnean Society, 86, 405) model, and the linear and log‐linear receptor noise limited models (Vorobyev & Osorio 1998, Proceedings of the Royal Society B, 265, 351; Vorobyev et al. 1998, Journal of Comparative Physiology A, 183, 621)) using a series of simulations, present a unified framework that extends and generalize current models, and provide an R package to facilitate the use of color vision models. When the specific requirements of each model are met, between‐model results are qualitatively and quantitatively similar. However, under many common scenarios of color measurements, models may generate spurious values. For instance, models that log‐transform data and use relative photoreceptor outputs are prone to generate spurious outputs when the stimulus photon catch is smaller than the background photon catch; and models may generate unrealistic predictions when the background is chromatic (e.g. leaf reflectance) and the stimulus is an achromatic low reflectance spectrum. Nonetheless, despite differences, all three models are founded on a similar set of assumptions. Based on that, I provide a new formulation that accommodates and extends models to any number of photoreceptor types, offers flexibility to build user‐defined models, and allows users to easily adjust chromaticity diagram sizes to account for changes when using different number of photoreceptors.

An aposematic colour‐polymorphic moth seen through the eyes of conspecifics and predators – Sensitivity and colour discrimination in a tiger moth

Abstract Although predation is commonly thought to exert the strongest selective pressure on coloration in aposematic species, sexual selection may also influence coloration. Specifically, polymorphism in aposematic species cannot be explained by natural selection alone. Males of the aposematic wood tiger moth (Arctia plantaginis) are polymorphic for hindwing coloration throughout most of their range. In Scandinavia, they display either white or yellow hindwings. Female hindwing coloration varies continuously from bright orange to red. Redder females and yellow males suffer least from bird predation. White males often have higher mating success than yellow males. Therefore, we ask whether females can discriminate the two male morphs by colour. Males approach females by following pheromone plumes from a distance, but search visually at short range. This raises the questions whether males discriminate female coloration and, in turn, whether female coloration is also sexually selected. Using electroretinograms, we found significantly larger retinal responses in male than female A. plantaginis, but similar spectral sensitivities in both sexes, with peaks in the UV (349 nm), blue (457 nm) and green (521 nm) wavelength range. According to colour vision models, conspecifics can discriminate white and yellow males as separate morphs, but not orange and red females. For moths and birds (Cyanistes caeruleus), white males are more conspicuous against green and brown backgrounds, mostly due to UV reflectivity, and red females are slightly more conspicuous than orange females. The costly red coloration among females is likely selected by predator pressure, not by conspecifics, whereas male colour polymorphism is probably maintained, at least partly, by the opposing forces of predation pressure favouring yellow males, and female preference for white males. Whether or not the preference for white males is based on visual cues requires further testing. The evolution of polymorphic aposematic animals can be better understood when the visual system of the species and their predators is taken into consideration. A plain language summary is available for this article.

Evidence for an impact of melanopsin activation on unique white perception.

Current models of human color vision only consider cone inputs at photopic light levels, yet it is unclear whether the recently discovered melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) contribute to color perception. Using a lab-made five-primary photostimulator that can independently control the stimulations of rods, cones, and ipRGCs in human retina, we determined the observer's unique white perception, an equilibrium point for signals arising from the opponent mechanisms of color vision, under different levels of melanopsin activation. We found changing melanopsin activation levels shifts the equilibrium point in the chromatic pathways. Our results suggest potential evidence for an impact of melanopsin activation on unique white perception and the existing color vision model for the periphery may need to be revised by incorporating melanopsin signaling.

Anther specializations related to the division of labor in Microlicia cordata (Spreng.) Cham. (Melastomataceae)

ABSTRACT In heterantherous flowers, some anthers have an attraction and feeding function, while others are related to plant reproduction. Microlicia cordata has dimorphic stamens organized in two cycles: the antesepalous one with large stamens and pink anthers, and the antepetalous one with small stamens and yellow anthers. Division of labor was analyzed using the parameters of structure, composition, amount and estimated viability of pollen, and the color of floral parts. The anthers of the pollinating stamens were larger than the anthers of the feeding stamens, although anatomically similar. There was a difference in the amount of pollen produced by the anthers of the two cycles, but no difference was found in pollen viability. Considering a bee color vision model, the color of the anthers of the pollinating stamens contrasted less with that of the corolla, and thus is probably less attractive to visitors. Conversely, the anthers of the feeding stamens and the ventral appendage of the connective of the pollinating stamens contrasted more with the corolla, presenting the same color to the pollinators. These results are in accordance with the idea of division of labor among anthers of heterantherous flowers, especially regarding the quantity of pollen and the color of the floral parts.