Color Vision System Research Articles

Color Recognition Achieved in Multiwavelength Controlled Plasmonic Optoelectronic Memristor for Neuromorphic Visual System

AbstractAn optoelectronic synaptic device with the color‐recognition ability is highly desired for achieving the high‐efficient neuromorphic color visual system. In order to realistically implement the functionality of retina (i.e., bipolar cells and cones photoreceptors), the exploration of multiwavelength controlled optoelectronic synaptic devices with fully light tunable ability would be sorely needed. Here, a multiwavelength controlled plasmonic optoelectronic memristor based on the size‐dependent localized surface plasmon resonance (LSPR) of metallic nanostructures is developed. The distinguishable red (R), green (G), and blue (B) light response behaviors can be achieved in this single device, which enables the realization of color image perception and memory functions. The RGB light‐strengthened synaptic plasticity can be depressed by ultraviolet light stimulations, relying on the effects of LSPR and optical excitation in WOx:Ag nanocomposites. Moreover, the visual attention for color (color discrimination) is realized in this memristor, which promotes the improvement of recognition accuracy during the color image recognition process. A new approach in developing multiwavelength controlled synaptic devices is provided here for highly efficient neuromorphic vision.

Epitaxially Growing 2D RGB Trichromatic Cocrystal Nanomeshes to Trigger Cross‐Modulation White Light Emission

Comprehensive SummaryConsidering their oriented crystalline structure and high luminescent efficiency, the exploration of multi‐component organic cocrystal systems with tunable supramolecular nanostructures and potential RGB light emission has emerged as a captivating but challenging subject. Here, we propose a straightforward synthetic strategy to precisely govern the assembly, structure and structure‐property relationship of organic cocrystals. By employing the single‐crystalline template‐assisted epitaxial growth (SCT‐EG) method, the two‐dimensional (2D) highly‐aligned cocrystal nanomeshes are firstly developed to afford an exceptional RGB trichromatic system, triggering cross‐modulation white light emission (WLE) with remarkable stability and regeneration capacity over six months. The transformation from random 1D microstructures to uniformly‐oriented 2D nanomeshes can be attributed to the regulatory competitive intermolecular π‐π, CT interactions, and partial H bond interactions among cocrystals. Moreover, the successful construction of 2D RGB trichromatic cocrystal nanomeshes system holds promise to generate full‐color display, which can function as multicolor inks for photonic dynamic recognition, information encryption, and decryption.

Neurexin-1-dependent circuit activity is required for the maintenance of photoreceptor subtype identity in Drosophila

In the human and Drosophila color vision system, each photoreceptor neuron (cone cell in humans and R7/R8 photoreceptor cell in Drosophila) makes a stochastic decision to express a single photopigment of the same family with the exclusion of the others. While recent studies have begun to reveal the mechanisms that specify the generation of cone subtypes during development in mammals, nothing is known about how the mosaic of mutually exclusive cone subtypes is maintained in the mammalian retina. In Drosophila, recent work has led to the identification of several intrinsic factors that maintain the identity of R8 photoreceptor subtypes in adults. Whether and how extrinsic mechanisms are involved, however, remain unknown. In this study, we present evidence that supports that the Drosophila transsynaptic adhesion molecule Neurexin 1 (Dnrx-1) is required non-cell autonomously in R8p subtypes for the maintenance of R8y subtype identity. Silencing the activity of R8p subtypes caused a phenotype identical to that in dnrx-1 mutants. These results support a novel role for Nrx-1-dependent circuit activity in mediating the communication between R8 photoreceptor subtypes for maintaining the subtype identity in the retina.

Invited Session III: Diversity in chromatic processing across the animal kingdom: Color vision in stomatopod crustaceans.

Stomatopod crustaceans, commonly known as mantis shrimp, have perhaps the most unusual color-vision systems of any animals. The uniqueness is possible because stomatopods have compound eyes. Here, each unit, or ommatidium, acts as an independent visual detector, with its own corneal lens, internal optics, and set of photoreceptors. Ommatidia tuned to different wavelengths can be individually placed in the eye to build unusual color systems. In mantis shrimps, the receptors responsible for color vision are limited to six parallel rows of ommatidia that together form an equatorial belt, called the midband. Various receptors in these ommatidia are tuned to eight narrow-band spectral channels in the visible spectrum plus up to four additional ultraviolet channels. Thus, there is a total of twelve different color receptors for color vision. How these color channels are analyzed in the complex set of optic lobes existing behind the retina is only partly understood. It appears that stomatopods use both opponent and labelled-line color channels. Oddly, these animals appear to have limited ability to discriminate between spectral lights, but they have outstanding color constancy. Color vision, and color processing, in stomatopods is probably unlike that of any other animal group.

Close to complete conservation of the brachyceran opsin repertoire in the stalk-eyed fly Teleopsis dalmanni.

Due to the unique morphology of their adult visual system, stalk-eyed flies represent an important model of exaggerated trait evolution through sexual selection. Early physiological measurements indicated wavelength sensitivity peaks in the ultraviolet (360 nm), blue (450), blue-green (490 nm), and red (>550 nm) ranges in the compound eye retina of the stalk-eyed fly Teleopsis dalmanni, consistent with the trichromatic color and broad range motion detection vision system of brachyceran Diptera. A previous study of dipteran opsin gene diversification, however, detected only homologs of members of the long wavelength range sensitive opsin subfamilies Rh2 and Rh6 in T. dalmanni. Here, I report findings from analyzing the most recent T. dalmanni genome assembly, which revealed the conservation of most brachyceran opsin homologs except for the UV wavelength range-sensitive homolog Rh4. These results and other examples highlight the caution that needs to be applied to gene loss conclusions.

Multi-Wavelength-Recognizable Memristive Devices via Surface Plasmon Resonance Effect for Color Visual System.

Photoelectric memristor has attracted many attentions thanks to their promising potential in optical communication chips and artificial vision systems. However, the implementation of an artificial visual system based on memristive devices remains a considerable challenge because most photoelectric memristors cannot recognize color. Herein, multi-wavelength recognizable memristive devices based on silver(Ag) nanoparticles (NPs) and porous silicon oxide (SiOx ) nanocomposites are presented. Rely on the effects of localized surface plasmon resonance (LSPR) and optical excitation of Ag NPs in SiOx , the set voltage of the device can be gradually reduced. Moreover, the current overshoot problem is alleviated to suppress conducting filament overgrowth after visible light irradiation with different wavelengths, resulting in diverse low resistance states (LRS). Taking advantage of the characteristics of controlled switching voltage and LRS resistance distribution, color image recognition is finally realized in the present work. X-ray photoelectron spectroscopy (XPS) and conductive atomic force microscopy (C-AFM) show that the light irradiation plays an important role on resistive switching (RS) process: the photo-assisted Ag ionization leads to a significant reduction of set voltage and overshoot current. This work provides an effective method toward the development of multi-wavelength-recognizable memristive devices for future artificial color vision system.

A Non-Gradual Development Process of Cicada Eyes at the End of the Fifth-Instar Nymphal Stage to Obtain Visual Ability.

Insects' visual system is directly related to ecology and critical for their survival. Some cicadas present obvious differences in color and ultrastructure of compound eyes between nymphal and adult stages, but little is known about when cicadas obtain their visual ability to deal with the novel above-ground habitat. We use transcriptome analyses and reveal that cicada Meimuna mongolica has a trichromatic color vision system and that the eyes undergo a non-gradual development process at the end of the 5th-instar nymphal stage. The white-eye 5th-instar nymphs (i.e., younger 5th-instar nymphs) have no visual ability because critical components of the visual system are deficient. The transformation of eyes toward possessing visual function takes place after a tipping point in the transition phase from the white-eye period to the subsequent red-eye period, which is related to a decrease of Juvenile Hormone. The period shortly after adult emergence is also critical for eye development. Key differentially-expressed genes related to phototransduction and chromophore synthesis play positive roles for cicadas to adapt to above-ground habitat. The accumulation of ommochromes corresponds to the color change of eyes from white to red and dark brown during the end of the 5th-instar nymphal period. Cuticle tanning leads to eye color changing from dark-brown to light-brown during the early adult stage. We hypothesize that the accumulation of ommochromes occurring at the end of 5th-instar nymphal stage and the early adult stage is not only for cicadas to obtain visual ability, but also is a secure strategy to cope with potential photodamage after emergence.

High diversity of arthropod colour vision: from genes to ecology.

Colour vision allows animals to use the information contained in the spectrum of light to control important behavioural decisions such as selection of habitats, food or mates. Among arthropods, the largest animal phylum, we find completely colour-blind species as well as species with up to 40 different opsin genes or more than 10 spectral types of photoreceptors, we find a large diversity of optical methods shaping spectral sensitivity, we find eyes with different colour vision systems looking into the dorsal and ventral hemisphere, and species in which males and females see the world in different colours. The behavioural use of colour vision shows an equally astonishing diversity. Only the neural mechanisms underlying this sensory ability seems surprisingly conserved—not only within the phylum, but even between arthropods and the other well-studied phylum, chordates. The papers in this special issue allow a glimpse into the colourful world of arthropod colour vision, and besides giving an overview this introduction highlights how much more research is needed to fill in the many missing pieces of this large puzzle.This article is part of the theme issue ‘Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods’.

Colour vision in stomatopod crustaceans.

The stomatopod crustaceans, or mantis shrimps, are colourful marine invertebrate predators. Their unusual compound eyes have dorsal and ventral regions resembling typical crustacean apposition designs separated by a unique region called the midband that consists of from two to six parallel rows of ommatidia. In species with six-row midbands, the dorsal four rows are themselves uniquely specialized for colour analysis. Rhabdoms of ommatidia in these rows are longitudinally divided into three distinct regions: an apical ultraviolet (UV) receptor, a shorter-wavelength middle tier receptor and a longer-wavelength proximal tier receptor. Each of the total of 12 photoreceptors has a different spectral sensitivity, potentially contributing to a colour-vision system with 12 channels. Mantis shrimps can discriminate both human-visible and UV colours, but with limited precision compared to other colour-vision systems. Here, we review the structure and function of stomatopod colour vision, examining the types of receptors present in a species, the spectral tuning of photoreceptors both within and across species, the neural analysis of colour and the genetics underlying the multiple visual pigments used for colour vision. Even today, after many decades of research into the colour vision of stomatopods, much of its operation and its use in nature remain a mystery. This article is part of the theme issue 'Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods'.

Mechanisms of spectral orientation in a diurnal dung beetle.

Ball rolling dung beetles use a wide range of cues to steer themselves along a fixed bearing, including the spectral gradient of scattered skylight that spans the sky. Here, we define the spectral sensitivity of the diurnal dung beetle Kheper lamarcki and use the information to explore the orientation performance under a range of spectral light combinations. We find that, when presented with spectrally diverse stimuli, the beetles primarily orient to the apparent brightness differences as perceived by their green photoreceptors. Under certain wavelength combinations, they also rely on spectral information to guide their movements, but the brightness and spectral directional information is never fully disentangled. Overall, our results suggest the use of a dichromatic, primitive colour vision system for the extraction of directional information from the celestial spectral gradient to support straight-line orientation.This article is part of the theme issue ‘Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods’.

Do You See What I See? Diversity in Human Color Perception.

In our tendency to discuss the objective properties of the external world, we may fail to notice that our subjective perceptions of those properties differ between individuals. Variability at all levels of the color vision system creates diversity in color perception, from discrimination to color matching, appearance, and subjective experience, such that each of us lives in a unique perceptual world. In this review, I discuss what is known about individual differences in color perception and its determinants, particularly considering genetically mediated variability in cone photopigments and the paradoxical effects of visual environments in both contributing to and counteracting individual differences. I make the case that, as well as being of interest in their own right and crucial for a complete account of color vision, individual differences can be used as a methodological tool in color science for the insights that they offer about the underlying mechanisms of perception.

Colour vision in stomatopod crustaceans: more questions than answers.

ABSTRACTStomatopod crustaceans, or mantis shrimps, are known for their extensive range of spectral sensitivity but relatively poor spectral discrimination. Instead of the colour-opponent mechanism of other colour vision systems, the 12 narrow-band colour channels they possess may underlie a different method of colour processing. We investigated one hypothesis in which the photoreceptors are proposed to act as individual wave-band detectors, interpreting colour as a parallel pattern of photoreceptor activation, rather than a ratiometric comparison of individual signals. This different form of colour detection has been used to explain previous behavioural tests in which low-saturation blue was not discriminated from grey, potentially because of similar activation patterns. Results here, however, indicate that the stomatopod Haptosquilla trispinosa was able to easily distinguish several colours, including blue of both high and low saturation, from greys. The animals did show a decrease in performance over time in an artificially lit environment, indicating plasticity in colour discrimination ability. This rapid plasticity, most likely the result of a change in opsin (visual pigment) expression, has now been noted in several animal lineages (both invertebrate and vertebrate) and is a factor we suggest needs attention and potential re-examination in any colour-based behavioural tests. As for stomatopods, it remains unclear why they achieve poor colour discrimination using the most comprehensive set of spectral sensitivities in the animal kingdom and also what form of colour processing they may utilise.

Insect visual sensitivity to long wavelengths enhances colour contrast of insects against vegetation

The sensitivity of animal photoreceptors to different wavelengths of light strongly influence the perceived visual contrast of objects in the environment. Outside of the human visual wavelength range, ultraviolet sensitivity in many species provides important and behaviourally relevant visual contrast between objects. However, at the opposite end of the spectrum, the potential advantage of red sensitivity remains unclear. We investigated the potential benefit of long wavelength sensitivity by modelling the visual contrast of a wide range of jewel beetle colours against flowers and leaves of their host plants to hypothetical insect visual systems. We find that the presence of a long wavelength sensitive photoreceptor increases estimated colour contrast, particularly of beetles against leaves. Moreover, under our model parameters, a trichromatic visual system with ultraviolet (λmax = 355 nm), short (λmax = 445 nm) and long (λmax = 600 nm) wavelength photoreceptors performed as well as a tetrachromatic visual system, which had an additional medium wavelength photoreceptor (λmax = 530 nm). When we varied λmax for the long wavelength sensitive receptor in a tetrachromatic system, contrast values between beetles, flowers and leaves were all enhanced with increasing λmax from 580 nm to at least 640 nm. These results suggest a potential advantage of red sensitivity in visual discrimination of insect colours against vegetation and highlight the potential adaptive value of long wavelength sensitivity in insects.

Testing the niche differentiation hypothesis in wild capuchin monkeys with polymorphic color vision

Abstract The polymorphic color vision system present in most North, Central, and South American monkeys is a textbook case of balancing selection, yet the mechanism behind it remains poorly understood. Previous work has established task-specific foraging advantages to different color vision phenotypes: dichromats (red-green colorblind) are more efficient foraging for invertebrates, while trichromats (color “normal” relative to humans) are more efficient foraging for “reddish” ripe fruit, suggesting that niche differentiation may underlie the maintenance of color vision variation. We explore a prediction of the niche differentiation hypothesis by asking whether dichromatic and trichromatic capuchin monkeys (Cebus imitator) diverge in their foraging activity budget, specifically testing whether dichromats forage more frequently for invertebrates and trichromats forage more frequently for “reddish” ripe fruit. To assess this, we analyze a large data set of behavioral scan samples (n = 21 984) from 48 wild adult female capuchins of known color vision genotype, dominance rank, and reproductive status, together with models of food conspicuity. We find no significant differences between dichromats and trichromats in the frequency of scans spent foraging for different food types but do find that nursing females forage less overall than cycling females. Our results suggest that the potential for color-vision-based niche differentiation in foraging time may be curtailed by the energetic requirements of reproduction, behavioral synchrony caused by group living, and/or individual preferences. While niche differentiation in activity budgets by color vision type is not apparent, fine-scale niche differentiation may be occurring. This research enhances our understanding of the evolutionary processes maintaining sensory polymorphisms.

Ultraviolet vision aids the detection of nutrient-dense non-signaling plant foods

To expand our understanding of what tasks are particularly helped by UV vision and may justify the costs of focusing high-energy light onto the retina, we used an avian-vision multispectral camera to image diverse vegetated habitats in search of UV contrasts that differ markedly from visible-light contrasts. One UV contrast that stood out as very different from visible-light contrasts was that of nutrient-dense non-signaling plant foods (such as young leaves and immature fruits) against their natural backgrounds. From our images, we calculated color contrasts between 62+ species of such foods and mature foliage for the two predominant color vision systems of birds, UVS and VS. We also computationally generated images of what a generalized tetrachromat, unfiltered by oil droplets, would see, by developing a new methodology that uses constrained linear least squares to solve for optimal weighted combinations of avian camera filters to mimic new spectral sensitivities. In all visual systems, we found that nutrient-dense non-signaling plant foods presented a lower, often negative figure-ground contrast in the UV channels, and a higher, often positive figure-ground contrast in the visible channels. Although a zero contrast may sound unhelpful, it can actually enhance color contrast when compared in a color opponent system to other channels with nonzero contrasts. Here, low or negative UV contrasts markedly enhanced color contrasts. We propose that plants may struggle to evolve better UV crypsis since UV reflectance from vegetation is largely specular and thus highly dependent on object orientation, shape, and texture.

Intrafloral Color Modularity in a Bee-Pollinated Orchid.

Flower color has been studied in different ecological levels of organization, from individuals to communities. However, it is unclear how color is structured at the intrafloral level. In bee-pollinated flowers, the unidirectional gradient in color purity and pollen mimicry are two common processes to explain intrafloral color patterns. Considering that floral traits are often integrated, usually reflecting evolutionary modules under pollinator-mediated selection, we hypothesize that such intrafloral color patterns are structured by intrafloral color modules as perceived by bee color vision system. Here, we studied the tropical bee-pollinated orchid Cattleya walkeriana, given its intrafloral color complexity and variation among individuals. Considering bee color vision, we investigated if intrafloral color modules arose among intrafloral patches (tip or base of the sepals, petals, and labellum). We expected a separate color module between the labellum patches (the main attractive structure in orchids) and petals and sepals. We measured the color reflectance and calculated the photoreceptor excitation, spectral purity, hue, and the chromatic contrast of the floral structures in the hexagon color model. Spectral purity (saturation) was higher in the labellum tip in comparison to petals and sepals, generating a unidirectional gradient. Labellum base presented a less saturated yellow UV-absorbing color, which may reflect a pollen mimicry strategy. C. walkeriana presented three intrafloral color modules corresponding to the color of petals and sepals, the color of the labellum tip, and the color of labellum base. These color modules were unrelated to the development of floral structures. Given the importance of intrafloral color patterns in bee attraction and guidance, our results suggest that intrafloral patterns could be the outcome of evolutionary color modularization under pollinator-mediated selection.

How Good Are RGB Cameras Retrieving Colors of Natural Scenes and Paintings?-A Study Based on Hyperspectral Imaging.

RGB digital cameras (RGB) compress the spectral information into a trichromatic system capable of approximately representing the actual colors of objects. Although RGB digital cameras follow the same compression philosophy as the human eye (OBS), the spectral sensitivity is different. To what extent they provide the same chromatic experiences is still an open question, especially with complex images. We addressed this question by comparing the actual colors derived from spectral imaging with those obtained with RGB cameras. The data from hyperspectral imaging of 50 natural scenes and 89 paintings was used to estimate the chromatic differences between OBS and RGB. The corresponding color errors were estimated and analyzed in the color spaces CIELAB (using the color difference formulas ΔE*ab and CIEDE2000), Jzazbz, and iCAM06. In CIELAB the most frequent error (using ΔE*ab) found was 5 for both paintings and natural scenes, a similarity that held for the other spaces tested. In addition, the distribution of errors across the color space shows that the errors are small in the achromatic region and increase with saturation. Overall, the results indicate that the chromatic errors estimated are close to the acceptance error and therefore RGB digital cameras are able to produce quite realistic colors of complex scenarios.

Color vision system to assess English walnut (Juglans Regia) kernel pellicle color

Abstract English walnut (Juglans regia) kernel pellicle color is an important component of consumer quality, as a breeding phenotype attribute, and a key factor affecting marketing price. It is part of the United States Department of Agriculture (USDA) grading criteria and it is assessed by trained Dried Fruit and Tree Nuts Association (DFA) of California inspectors, who visually segregate kernels into four DFA color categories: 1 (‘Extra light’), 2 (‘Light’), 3 (‘Light Amber’), and 4 (‘Amber’). The establishment of an objective and fast Color Visual System (CVS) will remove human variability and bias, adding consistency and can speed-up the color evaluation process. Therefore, a portable CVS was designed, built and its performance was evaluated using three datasets of kernels, with a diverse range of pellicle colors: 2,000 from a UC Davis seedling population, 1,238 from ‘Chandler’, and 857 from ‘Howard’ cultivars. Kernel pellicle color was measured using the DFA (1 to 4) visual scoring system, a colorimeter and the CVS. Relationships between these methods were analyzed using correlation, density plots, and stepwise logistic regression methodology was further applied to create a set of CVS kernel pellicle color prediction models, which can classify kernels into the DFA color categories. The CVS could segregate all 4095 kernel samples into the DFA color categories with an accuracy equal to 68.9 %. The use of independent prediction models per dataset significantly improved prediction: the ‘Chandler’ model was most accurate (88.8 %), followed by the seedling (80.4 %) and ‘Howard’ (75.1 %) models. Therefore, it is recommended that a cultivar-specific model be used to improve grading prediction accuracy. Model accuracy performance was further improved when the number of color categories was reduced to two categories by combining 1 (‘Extra Light’) and 2 (‘Light’) (Category 1), and 3 (‘Light Amber’) 4 (‘Amber’) (Category 2). Overall, the CVS used with a dataset-specific model described overall kernel pellicle color much better than a single colorimeter reading, making CVS a promising tool to assess kernel pellicle color. The CVS can be used as an objective and consistent method during commercial walnut kernel pellicle color grading and/or high-throughput phenotype breeding evaluation.

Algorithm for processing high definition images for food colourimetry

An algorithm was developed for image processing of High Definition (HD) images for food colourimetry applications. HD images help to capture detailed features and provide higher measurement accuracy. Dense image matrix of HD images makes image-processing complex and requires high-end data processing system. A two-step image cropping was found useful for rapid analysis of HD image and in reducing the computational power requirement. CIE Lab colourimetric parameters were obtained by transforming RGB image into CIE Lab image. Algorithm was used for image pre processing and was evaluated to reduce the image matrix size. Computing performance in terms of CPU, RAM and Disk usage was determined during the processing of HD images for colour extraction. At 1100 × 1100 image size, image processing was successfully completed while keeping the CPU usage within stable range. Algorithm was integrated into food colour vision system to determine CIE Lab values of skim milk powder.

Palm fruit colours are linked to the broad-scale distribution and diversification of primate colour vision systems.

A long-standing hypothesis in ecology and evolution is that trichromatic colour vision (the ability to distinguish red from green) in frugivorous primates has evolved as an adaptation to detect conspicuous (reddish) fruits. This could provide a competitive advantage over dichromatic frugivores which cannot distinguish reddish colours from a background of green foliage. Here, we test whether the origin, distribution and diversity of trichromatic primates is positively associated with the availability of conspicuous palm fruits, i.e. keystone fruit resources for tropical frugivores. We combine global data of colour vision, distribution and phylogenetic data for more than 400 primate species with fruit colour data for more than 1700 palm species, and reveal that species richness of trichromatic primates increases with the proportion of palm species that have conspicuous fruits, especially in subtropical African forests. By contrast, species richness of trichromats in Asia and the Americas is not positively associated with conspicuous palm fruit colours. Macroevolutionary analyses further indicate rapid and synchronous radiations of trichromats and conspicuous palms on the African mainland starting 10 Ma. These results suggest that the distribution and diversification of African trichromatic primates is strongly linked to the relative availability of conspicuous (versus non-conspicuous) palm fruits, and that interactions between primates and palms are related to the coevolutionary dynamics of primate colour vision systems and palm fruit colours.