Cortical mechanisms of colour vision

An Arduino-Powered Device for the Study of White Perception beyond the Visual Chromatic Critical Flicker Fusion Frequency

Arduino microcontrollers are used for a wide range of technological and biomedical applications, such as image classification, computer vision, brain-computer interaction and vision experiments. Here, we present a new cost-effective mini-device based on RGB LED flicker stimulation for the assessment of the chromatic temporal resolution of the visual function based on the concept of critical flicker fusion frequency (CFF). The assembly of the device and its testing in thirty young subjects demonstrate the steady white visual perception of a trichromatic flicker stimulus (mixture of red, green and blue stimuli) beyond the CFF. Macular function as measured by photo-stress recovery time (PRT) was found to be independent of the CFF measurements for red, green and blue lights. However, a statistical correlation was found between the contrast modulation for CFF for red and green stimuli and PRT. Finally, wavefront measurements demonstrate that high-order aberrations improve the temporal resolution of the visual function.

Changes in standing stability when wearing different colored glasses cannot be determined by participants' subjective preference - A crossover randomized single-blinded pilot study

BACKGROUND

The use of individually preferred colored glasses has gained popularity with the expectation that it may improve balance control and sports performance, however, the results of previous studies remain inconclusive.

AIM OF THE STUDY

In the present pilot study, we aimed to determine the association between participants' subjective preference and standing balance performance when wearing five different colored glasses.

METHODS

Thirteen participants stood on one or two legs on a pair of synchronized force platforms for 30 seconds with 60 seconds rest between the five-five randomized stance trials, while wearing red, blue, yellow, green, or transparent colored glasses. In addition to 7 CoP-related variables, we analyzed five features of EMG data from three lower limb muscles on both legs.

RESULTS

No significant effect of colored glasses was found. Some CoP (velocity: χ²(4, 13) = 10.086; p = 0.039; Kendall's W = 0.194, root mean square [RMS]: χ²(4, 13) = 12.278; p = 0.015; Kendall's W = 0.236) and EMG-related (RMS of biceps femoris: χ²(4, 13) = 13.006; p = 0.011; Kendall's W = 0.250) variables showed differences between the colored glass conditions during dominant-leg stance, however, participants failed to consecutively determine these differences in standing stability.

CONCLUSIONS

Overall, our results may suggest that lens color preference, irrespective of the color itself, may influence dominant leg standing balance most probably due to psychological factors, however, only subjective determination have no potential to determine the color of the glasses that would support the individual's standing balance the most.

Nonuniform and pathway-specific laminar processing of spatial frequencies in the primary visual cortex of primates

The neocortex comprises six cortical layers that play a crucial role in information processing; however, it remains unclear whether laminar processing is consistent across all regions within a single cortex. In this study, we demonstrate diverse laminar response patterns in the primary visual cortex (V1) of three male macaque monkeys when exposed to visual stimuli at different spatial frequencies (SFs). These response patterns can be categorized into two groups. One group exhibit suppressed responses in the output layers for all SFs, while the other type shows amplified responses specifically at high SFs. Further analysis suggests that both magnocellular (M) and parvocellular (P) pathways contribute to the suppressive effect through feedforward mechanisms, whereas amplification is specific to local recurrent mechanisms within the parvocellular pathway. These findings highlight the non-uniform distribution of neural mechanisms involved in laminar processing and emphasize how pathway-specific amplification selectively enhances representations of high-SF information in primate V1.

Current understanding of subclinical diabetic retinopathy informed by histology and high-resolution in vivo imaging

The escalating incidence of diabetes mellitus has amplified the global impact of diabetic retinopathy. There are known structural and functional changes in the diabetic retina that precede the fundus photography abnormalities which currently are used to diagnose clinical diabetic retinopathy. Understanding these subclinical alterations is important for effective disease management. Histology and high-resolution clinical imaging reveal that the entire neurovascular unit, comprised of retinal vasculature, neurons and glial cells, is affected in subclinical disease. Early functional manifestations are seen in the form of blood flow and electroretinography disturbances. Structurally, there are alterations in the cellular components of vasculature, glia and the neuronal network. On clinical imaging, changes to vessel density and thickness of neuronal layers are observed. How these subclinical disturbances interact and ultimately manifest as clinical disease remains elusive. However, this knowledge reveals potential early therapeutic targets and the need for imaging modalities that can detect subclinical changes in a clinical setting.

Are ipRGCs involved in human color vision? Hints from physiology, psychophysics, and natural image statistics

Human photoreceptors consist of cones, rods, and melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs). First studied in circadian regulation and pupillary control, ipRGCs project to a variety of brain centers suggesting a broader involvement beyond non-visual functions. IpRGC responses are stable, long-lasting, and with a particular codification of photoreceptor signals. In comparison with the transient and adaptive nature of cone and rod signals, ipRGCs' signaling might provide an ecological advantage to different attributes of color vision. Previous studies have indicated melanopsin's influence on visual responses yet its contribution to color perception in humans remains debated. We summarized evidence and hypotheses (from physiology, psychophysics, and natural image statistics) about direct and indirect involvement of ipRGCs in human color vision, by first briefly assessing the current knowledge about the role of melanopsin and ipRGCs in vision and codification of spectral signals. We then approached the question about melanopsin activation eliciting a color percept, discussing studies using the silent substitution method. Finally, we explore various avenues through which ipRGCs might impact color perception indirectly, such as through involvement in peripheral color matching, post-receptoral pathways, color constancy, long-term chromatic adaptation, and chromatic induction. While there is consensus about the role of ipRGCs in brightness perception, confirming its direct contribution to human color perception requires further investigation. We proposed potential approaches for future research, emphasizing the need for empirical validation and methodological thoroughness to elucidate the exact role of ipRGCs in human color vision.

Visual and cognitive processes contribute to age-related improvements in visual selective attention

Children (N = 103, 4-9 years, 59 females, 84% White, c. 2019) completed visual processing, visual feature integration (color, luminance, motion), and visual search tasks. Contrast sensitivity and feature search improved with age similarly for luminance and color-defined targets. Incidental feature integration improved more with age for color-motion than luminance-motion. Individual differences in feature search (β  = .11) and incidental feature integration (β  = .06) mediated age-related changes in conjunction visual search, an index of visual selective attention. These findings suggest that visual selective attention is best conceptualized as a series of developmental trajectories, within an individual, that vary by an object's defining features. These data have implications for design of educational and interventional strategies intended to maximize attention for learning and memory.

Binocular luster elicited by isoluminant chromatic stimuli relies on mechanisms similar to those in the achromatic case

The phenomenon of binocular luster can be evoked by simple dichoptic center-surround stimuli showing a luminance contrast difference between the eyes. Previous findings support the idea that this phenomenon is mediated by a low-level conflict mechanism that integrates the monocular signals from different types of contrast detector cells. Also, isoluminant stimuli with different chromatic contrasts between eyes can trigger sensations of luster. Here, we investigate whether the lustrous impression in such purely chromatic stimuli depends on interocular contrast differences and in particular on interocular contrast polarity pairings in a similar way as in the achromatic case. In our experiments, we measured the magnitude of the lustrous response using a series of isoluminant dichoptic center-ring-surround stimuli with varying ring width whose chromatic properties were varied along the red-green and blue-yellow cardinal directions. The trends in the data were very similar to those of our former study with achromatic stimuli, indicating similar mechanisms in both cases. The empirical luster data could also be predicted fairly well by a chromatic version of our interocular conflict model (with overall R2 values between 0.577 and 0.639), for which two different receptive field models were used, simulating the behavior of color-sensitive double-opponent cells in V1.

Technology and Integration Roadmap for Optoelectronic Memristor

Optoelectronic memristors (OMs) have emerged as a promising optoelectronic Neuromorphic computing paradigm, opening up new opportunities for neurosynaptic devices and optoelectronic systems. These OMs possess a range of desirable features including minimal crosstalk, high bandwidth, low power consumption, zero latency, and the ability to replicate crucial neurological functions such as vision and optical memory. By incorporating large-scale parallel synaptic structures, OMs are anticipated to greatly enhance high-performance and low-power in-memory computing, effectively overcoming the limitations of the von Neumann bottleneck. However, progress in this field necessitates a comprehensive understanding of suitable structures and techniques for integrating low-dimensional materials into optoelectronic integrated circuit platforms. This review aims to offer a comprehensive overview of the fundamental performance, mechanisms, design of structures, applications, and integration roadmap of optoelectronic synaptic memristors. By establishing connections between materials, multilayer optoelectronic memristor units, and monolithic optoelectronic integrated circuits, this review seeks to provide insights into emerging technologies and future prospects that are expected to drive innovation and widespread adoption in the near future.

Pupil responses to colorfulness are selectively reduced in healthy older adults

The alignment between visual pathway signaling and pupil dynamics offers a promising non-invasive method to further illuminate the mechanisms of human color perception. However, only limited research has been done in this area and the effects of healthy aging on pupil responses to the different color components have not been studied yet. Here we aim to address this by modelling the effects of color lightness and chroma (colorfulness) on pupil responses in young and older adults, in a closely controlled passive viewing experiment with 26 broad-spectrum digital color fields. We show that pupil responses to color lightness and chroma are independent from each other in both young and older adults. Pupil responses to color lightness levels are unaffected by healthy aging, when correcting for smaller baseline pupil sizes in older adults. Older adults exhibit weaker pupil responses to chroma increases, predominantly along the Green-Magenta axis, while relatively sparing the Blue-Yellow axis. Our findings complement behavioral studies in providing physiological evidence that colors fade with age, with implications for color-based applications and interventions both in healthy aging and later-life neurodegenerative disorders.

A deep new look at color

Bowers et al. counter deep neural networks (DNNs) as good models of human visual perception. From our color perspective we feel their view is based on three misconceptions: A misrepresentation of the state-of-the-art of color perception; the type of model required to move the field forward; and the attribution of shortcomings to DNN research that are already being resolved.

Differential encoding of temporally evolving color patterns across nearby V1 neurons

Whereas studies of the V1 cortex have focused mainly on neural line orientation preference, color inputs are also known to have a strong presence among these neurons. Individual neurons typically respond to multiple colors and nearby neurons have different combinations of preferred color inputs. However, the computations performed by V1 neurons on such color inputs have not been extensively studied. Here we aimed to address this issue by studying how different V1 neurons encode different combinations of inputs composed of four basic colors. We quantified the decoding accuracy of individual neurons from multi-electrode array recordings, comparing multiple individual neurons located within 2 mm along the vertical axis of the V1 cortex of the anesthetized rat. We found essentially all V1 neurons to be good at decoding spatiotemporal patterns of color inputs and they did so by encoding them in different ways. Quantitative analysis showed that even adjacent neurons encoded the specific input patterns differently, suggesting a local cortical circuitry organization which tends to diversify rather than unify the neuronal responses to each given input. Using different pairs of monocolor inputs, we also found that V1 neocortical neurons had a diversified and rich color opponency across the four colors, which was somewhat surprising given the fact that rodent retina express only two different types of opsins. We propose that the processing of color inputs in V1 cortex is extensively composed of multiple independent circuitry components that reflect abstract functionalities resident in the internal cortical processing rather than the raw sensory information per se.

Tracing a new path in the field of AI and robotics: mimicking human intelligence through chemistry. Part II: systems chemistry

Inspired by some traits of human intelligence, it is proposed that wetware approaches based on molecular, supramolecular, and systems chemistry can provide valuable models and tools for novel forms of robotics and AI, being constituted by soft matter and fluid states as the human nervous system and, more generally, life, is. Bottom-up mimicries of intelligence range from the molecular world to the multicellular level, i.e., from the Ångström (10 - 10 meters) to the micrometer scales (10 - 6 meters), and allows the development of unconventional chemical robotics. Whereas conventional robotics lets humans explore and colonise otherwise inaccessible environments, such as the deep oceanic abysses and other solar system planets, chemical robots will permit us to inspect and control the microscopic molecular and cellular worlds. This article suggests that systems made of properly chosen molecular compounds can implement all those modules that are the fundamental ingredients of every living being: sensory, processing, actuating, and metabolic networks. Autonomous chemical robotics will be within reach when such modules are compartmentalised and assembled. The design of a strongly intertwined web of chemical robots, with or without the involvement of living matter, will give rise to collective forms of intelligence that will probably reproduce, on a minimal scale, some sophisticated performances of the human intellect and will implement forms of "general AI." These remarkable achievements will require a productive interdisciplinary collaboration among chemists, biotechnologists, computer scientists, engineers, physicists, neuroscientists, cognitive scientists, and philosophers to be achieved. The principal purpose of this paper is to spark this revolutionary collaborative scientific endeavour.

How children learn to understand language meanings: a neural model of adult-child multimodal interactions in real-time

This article describes a biological neural network model that can be used to explain how children learn to understand language meanings about the perceptual and affective events that they consciously experience. This kind of learning often occurs when a child interacts with an adult teacher to learn language meanings about events that they experience together. Multiple types of self-organizing brain processes are involved in learning language meanings, including processes that control conscious visual perception, joint attention, object learning and conscious recognition, cognitive working memory, cognitive planning, emotion, cognitive-emotional interactions, volition, and goal-oriented actions. The article shows how all of these brain processes interact to enable the learning of language meanings to occur. The article also contrasts these human capabilities with AI models such as ChatGPT. The current model is called the ChatSOME model, where SOME abbreviates Self-Organizing MEaning.

Decoding of the neural representation of the visual RGB color model

RGB color is a basic visual feature. Here we use machine learning and visual evoked potential (VEP) of electroencephalogram (EEG) data to investigate the decoding features of the time courses and space location that extract it, and whether they depend on a common brain cortex channel. We show that RGB color information can be decoded from EEG data and, with the task-irrelevant paradigm, features can be decoded across fast changes in VEP stimuli. These results are consistent with the theory of both event-related potential (ERP) and P300 mechanisms. The latency on time course is shorter and more temporally precise for RGB color stimuli than P300, a result that does not depend on a task-relevant paradigm, suggesting that RGB color is an updating signal that separates visual events. Meanwhile, distribution features are evident for the brain cortex of EEG signal, providing a space correlate of RGB color in classification accuracy and channel location. Finally, space decoding of RGB color depends on the channel classification accuracy and location obtained through training and testing EEG data. The result is consistent with channel power value distribution discharged by both VEP and electrophysiological stimuli mechanisms.

Pixel-Domain Just Noticeable Difference Modeling with Heterogeneous Color Features

With the rapidly emerging user-generated images, perception compression for color image is an inevitable mission. Whilst in existing just noticeable difference (JND) models, color-oriented features are not fully taken into account for coinciding with HVS perception characteristics, such as sensitivity, attention, and masking. To fully imitate the color perception process, we extract color-related feature parameters as local features, including color edge intensity and color complexity, as well as region-wise features, including color area proportion, color distribution position and color distribution dispersion, and inherent feature irrelevant to color content called color perception difference. Then, the potential interaction among them is analyzed and modeled as color contrast intensity. To utilize them, color uncertainty and color saliency are envisaged to emanate from feature integration in the information communication framework. Finally, color and uncertainty saliency models are applied to improve the conventional JND model, taking the masking and attention effect into consideration. Subjective and objective experiments validate the effectiveness of the proposed model, delivering superior noise concealment capacity compared with start-of-the-art works.

Built environment color modulates autonomic and EEG indices of emotional response

Understanding built environment exposure as a component of environmental enrichment has significant implications for mental health, but little is known about the effects design characteristics have on our emotions and associated neurophysiology. Using a Cave Automatic Virtual Environment while monitoring indoor environmental quality (IEQ), 18 participants were exposed to a resting state (black), and two room scenes, control (white) and condition (blue), to understand if the color of the virtual walls affected self-report, autonomic nervous system, and central nervous system correlates of emotion. Our findings showed that exposure to the chromatic color condition (blue) compared to the achromatic control (white) and resting-state (black, no built environment) significantly increased the range in respiration and skin conductance response. We also detected a significant increase in alpha frontal midline power and frontal hemispheric lateralization relative to blue condition, and increased power spectral density across all electrodes in the blue condition for theta, alpha, and beta bandwidths. The ability for built environment design to modulate emotional response has the potential to deliver significant public health, economic, and social benefits to the entire community. The findings show that blue coloring of the built environment increases autonomic range and is associated with modulations of brain activity linked to emotional processing.

Green advertising is more environmentally friendly? The influence of advertising color on consumers' preferences for green products

The color of green product advertisements is an important factor affecting consumers' preferences. Based on the theory of the self-control system, this paper explores the influence mechanism and boundary conditions of green product ad color on consumers' preferences through three experiments. Experiment 1 tested the effect of advertisement color type (green/color) on consumers' preferences for green products. The results show that color ad can promote consumers' preferences for green products compared with green ad. Experiment 1 also analyzed the mediating role of the self-control system between advertisement color type (green/color) and consumers' preferences. Experiment 2 further clarified the boundary of the main effect. The effect of ad color (green/color) on consumers' preferences was only effective in the context of green products. Experiment 3 explored the moderating effect of green product type (egoistic/altruistic) on the main effect. The results show that only when the green product type is altruistic, the ad color type (green/color) can significantly affect consumers' preferences. This study is the first to link the ad color of green products with consumers' preferences. The findings confirm that the use of color ad for green products can elicit higher consumers' preferences than pure green ad, which enriches the research on the color of green product advertisements.

Computational modeling of color perception with biologically plausible spiking neural networks

Biologically plausible computational modeling of visual perception has the potential to link high-level visual experiences to their underlying neurons' spiking dynamic. In this work, we propose a neuromorphic (brain-inspired) Spiking Neural Network (SNN)-driven model for the reconstruction of colorful images from retinal inputs. We compared our results to experimentally obtained V1 neuronal activity maps in a macaque monkey using voltage-sensitive dye imaging and used the model to demonstrate and critically explore color constancy, color assimilation, and ambiguous color perception. Our parametric implementation allows critical evaluation of visual phenomena in a single biologically plausible computational framework. It uses a parametrized combination of high and low pass image filtering and SNN-based filling-in Poisson processes to provide adequate color image perception while accounting for differences in individual perception.

A simple model of binocular luster

The dichoptic combination of simple center–surround stimuli showing a contrast difference between eyes can trigger a lustrous impression in the fused percept, particularly when the contrast polarities in the two input images are of opposite sign. Recent developments suggest that the phenomenon of binocular luster results from a neural conflict between ON and OFF visual pathways at an early binocular level. Support for this idea was found in a previous study in which the empirical luster judgments strongly correlated with the predictions of an interocular conflict model which was based on such ON–OFF pairings. However, our original model could not account for the fact that weaker lustrous sensations can also be evoked by stimuli showing contrast polarities of same sign between eyes. In the present study we present an improved model that also includes ON–ON and OFF–OFF pairings. The predictive power of this model was tested in a series of four experiments, using a total of about 500 different center–ring–surround configurations as test stimuli. We found that, overall, our modified version accounts for more than 80% of the variance in the empirical luster judgments and that the former problems could be largely resolved. Our results further suggest a nonlinear transducer function for the binocular conflict signals.

Effects of acute high intraocular pressure on red-green and blue-yellow cortical color responses in non-human primates

Glaucoma is a leading cause of irreversible blindness worldwide, and intraocular pressure (IOP) is an established and modifiable risk factor for both chronic and acute glaucoma. The relationship between color vision deficits and chronic glaucoma has been described previously. However, the effects of acute glaucoma or acute primary angle closure, which has high prevalence in China, on color vision remains unclear. To address the above question, red-green or blue-yellow color responses in V1, V2, and V4 of seven rhesus macaques were monitored using intrinsic-signal optical imaging while monocular anterior chamber perfusions were performed to reversibly elevate IOP acutely over a clinically observed range of 30 to 90 mmHg. We found that the cortical population responses to both red-green and blue-yellow grating stimuli, systematically decreased as IOP increased from 30 to 90 mmHg. Although a similar decrement in magnitude was noted in V1, V2, and V4, blue-yellow responses were consistently more impaired than red-green responses at all levels of acute IOP elevation and in all monitored visual areas. This physiological study in non-human primates demonstrates that acute IOP elevations substantially depress the ability of the visual cortex to register color information. This effect is more severe for blue-yellow responses than for red-green responses, suggesting selective impairment of the koniocellular pathways compared with the parvocellular pathways. Together, we infer that blue-yellow color vision might be the most vulnerable visual function in acute glaucoma patients.

Luminance dependency of perceived color shift after color contrast adaptation caused by higher-order color channels

Color adaptation is a phenomenon in which, after prolonged exposure to a specific color (i.e. adaptation color), the perceived color shifts to approximately the opposite color direction of the adaptation color. Color adaptation is strongly related to sensitivity changes in photoreceptors, such as von Kries adaptation and cone-opponent mechanisms. On the other hand, the perceptual contrast of colors (e.g. perceptual saturation of the red-green direction) decreases after adaptation to a stimulus with spatial and/or temporal color modulation along the color direction. This phenomenon is referred to as color contrast adaptation. Color contrast adaptation has been used to investigate the representation of colors in the visual system. In the present study, we measured color perception after color contrast adaptation to stimuli with temporal color modulations along complicated color loci in a luminance-chromaticity plane. We found that, after the observers adapted to color modulations with different chromaticities at higher, medium, and lower luminance (e.g. temporal alternations among red, green, and red, each at a different luminance level), the chromaticity corresponding to perceptual achromaticity (the achromatic point) shifted to the same color direction as the adaptation chromaticity in each test stimulus luminance. In contrast, this luminance dependence of the achromatic point shift was not observed after adaptation to color modulations with more complex luminance-chromaticity correspondences (e.g. alternating red, green, red, green, and red, at five luminance levels, respectively). In addition, the occurrence or nonoccurrence of the luminance-dependent achromatic point shift was qualitatively predicted using a noncardinal model composed of channels preferring intermediate color directions between the cardinal chromaticity and luminance axes. These results suggest that the noncardinal channels are involved in the luminance-dependent perceived color shift after adaptation.

Non-cardinal color mechanism elicitation by stimulus shape: Bringing the S versus L+M color plane to the table

Neurons in the cortex typically respond best to elongated stimuli, or gratings, whereas neurons in the lateral geniculate nucleus (LGN) typically prefer circular stimuli, or spots. Further, neural mechanisms specifically tuned for non-cardinal colors largely do not emerge until the cortex; therefore, the use of gratings should better reveal non-cardinal color mechanisms. This hypothesis has been tested in the isoluminant color plane in macaque monkeys (Stoughton, Lafer-Sousa, Gagin, & Conway, 2012) and in the L–M versus L+M color plane in human subjects (Gegenfurtner & Kiper, 1992). Here, this hypothesis was tested in the third color plane, S versus L+M, in human subjects in two experiments. Experiment 1 tested 10 subjects across four directions in this color plane; Experiment 2 tested three subjects in eight to twelve color directions. Consistent with data from the other two color planes, in both experiments in the S versus L+M color plane, gratings revealed the presence of non-cardinal mechanisms more strongly than did spots.

Processing of visual statistics of naturalistic videos in macaque visual areas V1 and V4

Natural scenes are characterized by diverse image statistics, including various parameters of the luminance histogram, outputs of Gabor-like filters, and pairwise correlations between the filter outputs of different positions, orientations, and scales (Portilla–Simoncelli statistics). Some of these statistics capture the response properties of visual neurons. However, it remains unclear to what extent such statistics can explain neural responses to natural scenes and how neurons that are tuned to these statistics are distributed across the cortex. Using two-photon calcium imaging and an encoding-model approach, we addressed these issues in macaque visual areas V1 and V4. For each imaged neuron, we constructed an encoding model to mimic its responses to naturalistic videos. By extracting Portilla–Simoncelli statistics through outputs of both filters and filter correlations, and by computing an optimally weighted sum of these outputs, the model successfully reproduced responses in a subpopulation of neurons. We evaluated the selectivities of these neurons by quantifying the contributions of each statistic to visual responses. Neurons whose responses were mainly determined by Gabor-like filter outputs (low-level statistics) were abundant at most imaging sites in V1. In V4, the relative contribution of higher order statistics, such as cross-scale correlation, was increased. Preferred image statistics varied markedly across V4 sites, and the response similarity of two neurons at individual imaging sites gradually declined with increasing cortical distance. The results indicate that natural scene analysis progresses from V1 to V4, and neurons sharing preferred image statistics are locally clustered in V4.

Unsupervised learning of haptic material properties

When touching the surface of an object, its spatial structure translates into a vibration on the skin. The perceptual system evolved to translate this pattern into a representation that allows to distinguish between different materials. Here, we show that perceptual haptic representation of materials emerges from efficient encoding of vibratory patterns elicited by the interaction with materials. We trained a deep neural network with unsupervised learning (Autoencoder) to reconstruct vibratory patterns elicited by human haptic exploration of different materials. The learned compressed representation (i.e., latent space) allows for classification of material categories (i.e., plastic, stone, wood, fabric, leather/wool, paper, and metal). More importantly, classification performance is higher with perceptual category labels as compared to ground truth ones, and distances between categories in the latent space resemble perceptual distances, suggesting a similar coding. Crucially, the classification performance and the similarity between the perceptual and the latent space decrease with decreasing compression level. We could further show that the temporal tuning of the emergent latent dimensions is similar to properties of human tactile receptors.

Temporal dynamics of the neural representation of hue and luminance polarity

Hue and luminance contrast are basic visual features. Here we use multivariate analyses of magnetoencephalography data to investigate the timing of the neural computations that extract them, and whether they depend on common neural circuits. We show that hue and luminance-contrast polarity can be decoded from MEG data and, with lower accuracy, both features can be decoded across changes in the other feature. These results are consistent with the existence of both common and separable neural mechanisms. The decoding time course is earlier and more temporally precise for luminance polarity than hue, a result that does not depend on task, suggesting that luminance contrast is an updating signal that separates visual events. Meanwhile, cross-temporal generalization is slightly greater for representations of hue compared to luminance polarity, providing a neural correlate of the preeminence of hue in perceptual grouping and memory. Finally, decoding of luminance polarity varies depending on the hues used to obtain training and testing data. The pattern of results is consistent with observations that luminance contrast is mediated by both L-M and S cone sub-cortical mechanisms.

Function-specific projections from V2 to V4 in macaques

Previous studies have revealed modular projections from area V2 to area V4 in macaques. Specifically, V2 neurons in cytochrome oxidase (CO)-rich thin and CO-sparse pale stripes project to distinct regions in V4. However, how these modular projections relate to the functional subcompartments of V4 remains unclear. In this study, we injected retrograde fluorescent tracers into V4 regions with different functional properties (color, orientation, and direction) that were identified with intrinsic signal optical imaging (ISOI). We examined the labeled neurons in area V2 and their locations with respect to the CO patterns. Covariation was observed between the functional properties of the V4 injection sites and the numbers of labeled neurons in particular CO stripes. This covariation indicates that the color domains in V4 mainly received inputs from thin stripes in V2, whereas V4 orientation domains received inputs from pale stripes. Although motion-sensitive domains are present in both V2 and V4, our results did not reveal a functional specific feedforward projection between them. These results confirmed previous findings of modular projections from V2 to V4 and provided functional specificity for these anatomical projections. Together, these findings indicate that color and form remain separate in ventral mid-level visual processing.

A neuro-computational model of visual attention with multiple attentional control sets

In numerous activities, humans need to attend to multiple sources of visual information at the same time. Although several recent studies support the evidence of this ability, the mechanism of multi-item attentional processing is still a matter of debate and has not been investigated much by previous computational models. Here, we present a neuro-computational model aiming to address specifically the question of how subjects attend to two items that deviate defined by feature and location. We simulate the experiment of Adamo et al. (2010) which required subjects to use two different attentional control sets, each a combination of color and location. The structure of our model is composed of two components "attention" and "decision-making". The important aspect of our model is its dynamic equations that allow us to simulate the time course of processes at a neural level that occur during different stages until a decision is made. We analyze in detail the conditions under which our model matches the behavioral and EEG data from human subjects. Consistent with experimental findings, our model supports the hypothesis of attending to two control settings concurrently. In particular, our model proposes that initially, feature-based attention operates in parallel across the scene, and only in ongoing processing, a selection by the location takes place.

Emergence of crowding: The role of contrast and orientation salience

Crowding causes difficulties in judging attributes of an object surrounded by other objects. We investigated crowding for stimuli that isolated either S-cone or luminance mechanisms or combined them. By targeting different retinogeniculate mechanisms with contrast-matched stimuli, we aim to determine the earliest site at which crowding emerges. Discrimination was measured in an orientation judgment task where Gabor targets were presented parafoveally among flankers. In the first experiment, we assessed flanked and unflanked orientation discrimination thresholds for pure S-cone and achromatic stimuli and their combinations. In the second experiment, to capture individual differences, we measured unflanked detection and orientation sensitivity, along with performance under flanker interference for stimuli containing luminance only or combined with S-cone contrast. We confirmed that orientation sensitivity was lower for unflanked S-cone stimuli. When flanked, the pattern of results for S-cone stimuli was the same as for achromatic stimuli with comparable (i.e. low) contrast levels. We also found that flanker interference exhibited a genuine signature of crowding only when orientation discrimination threshold was reliably surpassed. Crowding, therefore, emerges at a stage that operates on signals representing task-relevant featural (here, orientation) information. Because luminance and S-cone mechanisms have very different spatial tuning properties, it is most parsimonious to conclude that crowding takes place at a neural processing stage after they have been combined.

Establishing a New Link between Fuzzy Logic, Neuroscience, and Quantum Mechanics through Bayesian Probability: Perspectives in Artificial Intelligence and Unconventional Computing

Human interaction with the world is dominated by uncertainty. Probability theory is a valuable tool to face such uncertainty. According to the Bayesian definition, probabilities are personal beliefs. Experimental evidence supports the notion that human behavior is highly consistent with Bayesian probabilistic inference in both the sensory and motor and cognitive domain. All the higher-level psychophysical functions of our brain are believed to take the activities of interconnected and distributed networks of neurons in the neocortex as their physiological substrate. Neurons in the neocortex are organized in cortical columns that behave as fuzzy sets. Fuzzy sets theory has embraced uncertainty modeling when membership functions have been reinterpreted as possibility distributions. The terms of Bayes' formula are conceivable as fuzzy sets and Bayes' inference becomes a fuzzy inference. According to the QBism, quantum probabilities are also Bayesian. They are logical constructs rather than physical realities. It derives that the Born rule is nothing but a kind of Quantum Law of Total Probability. Wavefunctions and measurement operators are viewed epistemically. Both of them are similar to fuzzy sets. The new link that is established between fuzzy logic, neuroscience, and quantum mechanics through Bayesian probability could spark new ideas for the development of artificial intelligence and unconventional computing.

Electrophysiological evidence for higher-level chromatic mechanisms in humans

Color vision in humans starts with three types of cones (short [S], medium [M], and long [L] wavelengths) in the retina and three retinal and subcortical cardinal mechanisms, which linearly combine cone signals into the luminance channel (L + M), the red-green channel (L - M), and the yellow-blue channel (S-(L + M)). Chromatic mechanisms at the cortical level, however, are less well characterized. The present study investigated such higher-order chromatic mechanisms by recording electroencephalograms (EEGs) on human observers in a noise masking paradigm. Observers viewed colored stimuli that consisted of a target embedded in noise. Color directions of the target and noise varied independently and systematically in an isoluminant plane of color space. The target was flickering on-off at 3 Hz, eliciting steady-state visual evoked potential (SSVEP) responses. As a result, the masking strength could be estimated from the SSVEP amplitude in the presence of 6 Hz noise. Masking was strongest (i.e. target eliciting smallest SSVEPs) when the target and noise were along the same color direction, and was weakest (i.e. target eliciting highest SSVEPs) when the target and noise were along orthogonal directions. This pattern of results was observed both when the target color varied along the cardinal and intermediate directions, which is evidence for higher-order chromatic mechanisms tuned to intermediate axes. The SSVEP result can be well predicted by a model with multiple broadly tuned chromatic mechanisms. In contrast, a model with only cardinal mechanisms failed to account for the data. These results provide strong electrophysiological evidence for multiple chromatic mechanisms in the early visual cortex of humans.

Neural mechanism of spatio-chromatic opponency in the Drosophila amacrine neurons

Visual animals detect spatial variations of light intensity and wavelength composition. Opponent coding is a common strategy for reducing information redundancy. Neurons equipped with both spatial and spectral opponency have been identified in vertebrates but not yet in insects. The Drosophila amacrine neuron Dm8 was recently reported to show color opponency. Here, we demonstrate Dm8 exhibits spatio-chromatic opponency. Antagonistic convergence of the direct input from the UV-sensing R7s and indirect input from the broadband receptors R1-R6 through Tm3 and Mi1 is sufficient to confer Dm8's UV/Vis (ultraviolet/visible light) opponency. Using high resolution monochromatic stimuli, we show the pale and yellow subtypes of Dm8s, inheriting retinal mosaic characteristics, have distinct spectral tuning properties. Using 2D white-noise stimulus and reverse correlation analysis, we found that the UV receptive field (RF) of Dm8 has a center-inhibition/surround-excitation structure. In the absence of UV-sensing R7 inputs, the polarity of the RF is inverted owing to the excitatory input from the broadband photoreceptors R1-R6. Using a new synGRASP method based on endogenous neurotransmitter receptors, we show that neighboring Dm8s form mutual inhibitory connections mediated by the glutamate-gated chloride channel GluClα, which is essential for both Dm8's spatial opponency and animals' phototactic behavior. Our study shows spatio-chromatic opponency could arise in the early visual stage, suggesting a common information processing strategy in both invertebrates and vertebrates.

A new transformation of cone responses to opponent color responses

It is widely agreed that the color vision process moves quickly from cone receptors to opponent color cells in the retina and lateral geniculate nucleus. Many workers have proposed the transformation or coding of long, medium, short (LMS) cone responses to r - g, y - b opponent color chromatic responses (unique hues) on the following basis: That L, M, S cones represent Red, Green, and Blue hues, with Yellow represented by (L + M), while r - g and y - b represent the opponent pairs of unique hues. The traditional coding from cones to opponent colors is that L - M gives r - g, while (L + M) - S gives y - b. This convention is open to several criticisms, and a new coding is required. A literature search produced 16 studies of cone responses LMS and 15 studies of spectral (i.e., ygb) opponent color chromatic responses, in terms of response wavelength peaks. Comparative analysis of the two sets of studies shows the means are almost identical (within 3 nm; i.e., L = y, M = g, S = b). Further, the response curves of LMS are very similar shapes to ygb. In sum, each set can directly transform to the other on this proposed coding: (S + L) - M gives r - g, while L - S gives y - b. This coding activates neural operations in the cardinal directions r - g and y - b.

Moving Binary-Color Heterojunction for Spatiotemporal Multilevel Encryption via Directional Swelling and Anion Exchange

Naked-eye-visible color/graphical patterns have shown significant potential in optical encryption. However, current strategies for optical encryption are usually based on static or homogeneous information, which limits their applications in multivalue coding and advanced confidential encryption. Here, we propose a concept of spatiotemporally tunable optical encryption by constructing a multilevel binary-color spatial heterojunction pattern into the time dimension. This multiple coding strategy can enable a simple pattern much more difficult to be counterfeited and keep the facile authentication by naked eyes or smartphone at the same time. As a proof of concept, we fabricated a moving red-green heterojunction pattern by elaborately utilizing the directional swelling process of a poly(dimethylsiloxane) matrix in organic solvents and the ion-exchange property of a perovskite quantum dot wrapped in it. We demonstrate that trioctylphosphine plays a significant role in endowing the red-green heterojunction with a stable and distinct interface for better perception by eyes. The directional swelling and following ion-exchange dynamics in the local interface indicate that we can tailor the movement of the binary-color heterojunction in a quasi-continuous way via orthogonal variables of swelling ratio and ion concentration gradient. The concept of heterojunction-based multivalue optical encryption in the time dimension is independent with other dimensions, indicating a promising compatibility with the existing optical encryption systems.

Image motion with color contrast suffices to elicit an optokinetic reflex in Xenopus laevis tadpoles

The optokinetic reflex is a closed-loop gaze-stabilizing ocular motor reaction that minimizes residual retinal image slip during vestibulo-ocular reflexes. In experimental isolation, the reflex is usually activated by motion of an achromatic large-field visual background with strong influence of radiance contrast on visual motion estimation and behavioral performance. The presence of color in natural environments, however, suggests that chromatic cues of visual scenes provide additional parameters for image motion detection. Here, we employed Xenopus laevis tadpoles to study the influence of color cues on the performance of the optokinetic reflex and multi-unit optic nerve discharge during motion of a large-field visual scene. Even though the amplitude of the optokinetic reflex decreases with smaller radiance contrast, considerable residual eye movements persist at the ‘point of equiluminance’ of the colored stimuli. Given the color motion preferences of individual optic nerve fibers, the underlying computation potentially originates in retinal circuits. Differential retinal ganglion cell projections and associated ocular motor signal transformation might further reinforce the color dependency in conceptual correspondence with head/body optomotor signaling. Optokinetic reflex performance under natural light conditions is accordingly influenced by radiance contrast as well as by the color composition of the moving visual scene.

Color for object recognition: Hue and chroma sensitivity in the deep features of convolutional neural networks

In this work, we examined the color tuning of units in the hidden layers of AlexNet, VGG-16 and VGG-19 convolutional neural networks and their relevance for the successful recognition of an object. We first selected the patches for which the units are maximally responsive among the 1.2 M images of the ImageNet training dataset. We segmented these patches using a k-means clustering algorithm on their chromatic distribution. Then we independently varied the color of these segments, both in hue and chroma, to measure the unit's chromatic tuning. The models exhibited properties at times similar or opposed to the known chromatic processing of biological system. We found that, similarly to the most anterior occipital visual areas in primates, the last convolutional layer exhibited high color sensitivity. We also found the gradual emergence of single to double opponent kernels. Contrary to cells in the visual system, however, these kernels were selective for hues that gradually transit from being broadly distributed in early layers, to mainly falling along the blue-orange axis in late layers. In addition, we found that the classification performance of our models varies as we change the color of our stimuli following the models' kernels properties. Performance was highest for colors the kernels maximally responded to, and images responsible for the activation of color sensitive kernels were more likely to be mis-classified as we changed their color. These observations were shared by all three networks, thus suggesting that they are general properties of current convolutional neural networks trained for object recognition.

Color Vision: Decoding Color Space

A new study has used magnetoencephalography to track cortical responses to color as they emerge in time. Similarities and differences within these neural responses parallel characteristics of the perceptual experience of color.

Color vision

Color is a fundamental aspect of normal visual experience. This chapter provides an overview of the role of color in human behavior, a survey of current knowledge regarding the genetic, retinal, and neural mechanisms that enable color vision, and a review of inherited and acquired defects of color vision including a discussion of diagnostic tests.

Plasticity in perception: insights from color vision deficiencies

Inherited color vision deficiencies typically result from a loss or alteration of the visual photopigments absorbing light and thus impact the very first step of seeing. There is growing interest in how subsequent steps in the visual pathway might be calibrated to compensate for the altered receptor signals, with the possibility that color coding and color percepts might be less severely impacted than the receptor differences predict. These compensatory adjustments provide important insights into general questions about sensory plasticity and the sensory and cognitive processes underlying how we experience color.

The role of contrast polarities in binocular luster: Low-level and high-level processes

The binocular fusion of two center-surround configurations, where one center is brighter, the other darker than the common surround, leads to a strong impression of luster in the central patch. Without reversed contrast polarities of the center patches, this impression is much weaker or even absent. However, we observed that in the latter case the perceived luster can be considerably enhanced by enclosing both centers with a thin ring of fixed luminance. Compared to the standard stimulus, this center-ring-surround configuration shows much less binocular rivalry and the luster has also a different, more glass-like material quality. In a psychophysical experiment, we examined how the magnitude of the lustrous response depends on the width of the ring, both in stimuli with reversed and consistent contrast polarities. It has been proposed that binocular luster results from a neuronal conflict between ON and OFF visual pathways. To test this hypothesis with respect to our data, we developed a simple model to estimate the amount of interocular conflict resulting from a given binocular stimulus pair and applied it to all stimuli used in the experiment. We found strong correlations between the interocular conflict measure and the strength of luster observed in the experiment, suggesting that a common low-level mechanism determines the magnitude of the lustrous response. Regarding the differences in the perceived material quality of the lustrous impressions, we discuss evidence indicating that high-level processes are involved that promote the visual system's interpretation of the ring-stimuli as a certain depth-segmented 3D scene.

The transition from feature to object: Storage unit in visual working memory depends on task difficulty

Visual working memory (VWM) is a cognitive memory buffer for temporarily processing and storing visual information. Previous studies suggest that its capacity is severely limited, and there is an ongoing debate on whether the storage capacity is object-based or feature-based in VWM. In this study, a change-detection task was employed to investigate whether and how task difficulty can affect VWM, specifically, its capacity and the unit of storage. Task difficulty was manipulated through the set size of memory items, memory fidelity required by the resolution of representation and the type of feature tested. We examined two types of stimuli: the single-feature type, where each memory item was composed of a single feature (color or shape), and the conjunctive-feature type, where each item was composed of a conjunction of two features (colored shape). Experiment 1 replicated the previous findings that memory capacity for colors was larger than shapes, and decreased with the resolution demand regardless of the type of stimuli. In Experiment 2, we analyzed and compared the results from single-feature items and conjunctive-feature items in the low- and high-resolution conditions while controlling for the number of to-be-remembered features. By directly matching the estimated capacity based on an object-unit and a feature-unit with the theoretical prediction, the results showed that the unit storage in VWM tended to be feature-based with low task difficulty, and to be object-based with high task difficulty. This suggests that VWM is dynamic and flexible, dependent on the load of the current task.

Neural correlates of perceptual color inferences as revealed by #thedress

Color constancy involves disambiguating the spectral characteristics of lights and surfaces, for example to distinguish red in white light from white in red light. Solving this problem appears especially challenging for bluish tints, which may be attributed more often to shading, and this bias may underlie the individual differences in whether people described the widely publicized image of #thedress as blue-black or white-gold. To probe these higher-level color inferences, we examined neural correlates of the blue-bias, using frequency-tagging and high-density electroencephalography to monitor responses to 3-Hz alternations between different color versions of #thedress. Specifically, we compared relative neural responses to the original “blue” dress image alternated with the complementary “yellow” image (formed by inverting the chromatic contrast of each pixel). This image pair produced a large modulation of the electroencephalography amplitude at the alternation frequency, consistent with a perceived contrast difference between the blue and yellow images. Furthermore, decoding topographical differences in the blue-yellow asymmetries over occipitoparietal channels predicted blue-black and white-gold observers with over 80% accuracy. The blue-yellow asymmetry was stronger than for a “red” versus “green” pair matched for the same component differences in L versus M or S versus LM chromatic contrast as the blue-yellow pair and thus cannot be accounted for by asymmetries within either precortical cardinal mechanism. Instead, the results may point to neural correlates of a higher-level perceptual representation of surface colors.

Anatomy and Physiology of Macaque Visual Cortical Areas V1, V2, and V5/MT: Bases for Biologically Realistic Models

The cerebral cortex of primates encompasses multiple anatomically and physiologically distinct areas processing visual information. Areas V1, V2, and V5/MT are conserved across mammals and are central for visual behavior. To facilitate the generation of biologically accurate computational models of primate early visual processing, here we provide an overview of over 350 published studies of these three areas in the genus Macaca, whose visual system provides the closest model for human vision. The literature reports 14 anatomical connection types from the lateral geniculate nucleus of the thalamus to V1 having distinct layers of origin or termination, and 194 connection types between V1, V2, and V5, forming multiple parallel and interacting visual processing streams. Moreover, within V1, there are reports of 286 and 120 types of intrinsic excitatory and inhibitory connections, respectively. Physiologically, tuning of neuronal responses to 11 types of visual stimulus parameters has been consistently reported. Overall, the optimal spatial frequency (SF) of constituent neurons decreases with cortical hierarchy. Moreover, V5 neurons are distinct from neurons in other areas for their higher direction selectivity, higher contrast sensitivity, higher temporal frequency tuning, and wider SF bandwidth. We also discuss currently unavailable data that could be useful for biologically accurate models.

Blue blood, red blood. How does the color of an emotional scene affect visual attention and pupil size?

The function of color in the processing of emotional scenes is not entirely clear. While there are studies showing that color matters in terms of the capture of covert attention by emotional stimuli, the impact of color on fixation patterns, reflecting overt attention, is unresolved. Studies on the role of color in evoking emotional response have also produced mixed results. Here, we aimed to explore how image color and content influence pupillary response and the engagement of overt visual attention. In the first experiment, we examined the pupillary reaction to neutral images (intact and phase scrambled) in three color variants (natural, abnormal, and grayscale). In the second experiment, we investigated the pupillary changes and fixation pattern in response to images of different valence (neutral, positive, and negative), again in three color versions. The results showed that pupillary responses were influenced by both content and the color of the images. The pupillary response to phase-scrambled images did not differ between the color versions. Intact neutral and positive images, but not negative ones, evoked smaller pupil responses if they were presented in abnormal colors rather than natural ones. The initial capture of attention by emotional content depended on the color version, whereas holding of attention was affected solely by the emotional valence. Thus, color changes the physiological response to images, particularly low-arousing ones, and modulates the initial engagement of attention by image content.

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."

What underlies visual selective attention development? Evidence that age-related improvements in visual feature integration influence visual selective attention performance

Visual selective attention (VSA) improves across childhood. Conjunction search tasks require integrating multiple visual features in order to find a target among distractors and are often used to measure VSA. Motivated by the visual system's architecture and developmental changes in neural connectivity, we predicted that feature integration across separate visual pathways (e.g., color and motion) should develop later than feature integration within the same visual pathways (e.g., luminance and motion). A total of 89 4- to 10-year-old children completed a visual search task that manipulated whether feature integration was between separate parallel visual pathways or within the same visual pathway. We first examined whether color-motion integration was associated with a performance cost relative to luminance-motion integration across childhood. We found that color-motion integration was worse than luminance-motion integration in early childhood but that this difference decreased with age. We also examined whether luminance-motion and color-motion visual search performance developed differently across childhood. Reaction time (RT) visual search slopes for the luminance-motion condition were both stable across childhood and steeper overall than those for the color-motion condition. In contrast, RT search slopes for the color-motion condition became steeperincrease across childhood. Finally, we found that age-related improvements in color-motion integration, relative to luminance-motion integration, were associated with longer color-motion search rates across childhood. These data suggest that age-related improvements in color-motion feature integration may increase competition between color-motion targets and distractors, thereby increasing the amount of time needed to process distractors as nontargets during the selection process.

The promises and perils of automated facial action coding in studying children's emotions

Computer vision algorithms have made tremendous advances in recent years. We now have algorithms that can detect and recognize objects, faces, and even facial actions in still images and video sequences. This is wonderful news for researchers that need to code facial articulations in large data sets of images and videos, because this task is time consuming and can only be completed by expert coders, making it very expensive. The availability of computer algorithms that can automatically code facial actions in extremely large data sets also opens the door to studies in psychology and neuroscience that were not previously possible, for example, to study the development of the production of facial expressions from infancy to adulthood within and across cultures. Unfortunately, there is a lack of methodological understanding on how these algorithms should and should not be used, and on how to select the most appropriate algorithm for each study. This article aims to address this gap in the literature. Specifically, we present several methodologies for use in hypothesis-based and exploratory studies, explain how to select the computer algorithms that best fit to the requirements of our experimental design, and detail how to evaluate whether the automatic annotations provided by existing algorithms are trustworthy. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Color vision in insects: insights from Drosophila

Color vision is an important sensory capability that enhances the detection of contrast in retinal images. Monochromatic animals exclusively detect temporal and spatial changes in luminance, whereas two or more types of photoreceptors and neuronal circuitries for the comparison of their responses enable animals to differentiate spectral information independent of intensity. Much of what we know about the cellular and physiological mechanisms underlying color vision comes from research on vertebrates including primates. In insects, many important discoveries have been made, but direct insights into the physiology and circuit implementation of color vision are still limited. Recent advances in Drosophila systems neuroscience suggest that a complete insect color vision circuitry, from photoreceptors to behavior, including all elements and computations, can be revealed in future. Here, we review fundamental concepts in color vision alongside our current understanding of the neuronal basis of color vision in Drosophila, including side views to selected other insects.