Biology subjects

Morimoto, T.

Publications and source records attributed to Morimoto, T..

27 records · Page 2Linked to original sources

bioRxiv2022

Invariant categorical color regions across illuminant change coincide with focal colors

Are there regions in a color space where color categories are invariant across illuminant changes? If so, what characteristics make them more stable than other regions? To address these questions, we asked observers to give a color name to 424 colored surfaces, presented one at a time, under various chromatic illuminants. Results showed a high degree of categorical color constancy, especially under illuminants that occur in the natural environment. It was also shown that surfaces selected as a focal color (the best example of a color category) are more resistant to illuminant change than non-focal color samples. This might imply that categorically invariant regions might have become focal colors to facilitate object identification and communication with others under a variety of lighting environments. We additionally ran an asymmetric color matching experiment to quantify the shift of color appearance induced by illuminant changes using surfaces that were all named gray, thereby disentangling the appearance-based color constancy from the categorical color constancy (which are often confounded). Results suggested that the appearance of color samples largely shifted due to illuminant changes even though all samples were named gray; showing that the constancy of a color category is substantially more robust than the constancy of color appearance.

neuroscience↗

bioRxiv2021

Hyperspectral characterisation of natural illumination in woodland and forest environments

Light in nature is complex and dynamic, and varies along spectrum, space, direction, and time. While both spectrally resolved measurements and spatially resolved measurements are widely available, spectrally and spatially resolved measurements are technologically more challenging. Here, we present a portable imaging system using off-the-shelf components to capture the full spherical light environment in a spectrally and spatially resolved fashion. The method relies on imaging the 4{pi}-steradian light field reflected from a mirrored chrome sphere using a commercial hyperspectral camera (400-1000 nm) from multiple directions and an image-processing pipeline for extraction of the mirror sphere, removal of saturated pixels, correction of specular reflectance of the sphere, promotion to a high dynamic range, correction of misalignment of images, correction of intensity compression, erasure of the imaging system, unwrapping of the spherical images, filling-in blank regions, and stitching images collected from different angles. We applied our method to Wytham Woods, an ancient semi-natural woodland near Oxford, UK. We acquired a total of 168 images in two sites with low and high abundance of ash, leading to differences in canopy, leading to a total 14 hyperspectral light probes. Our image-processing pipeline corrected small (<3 {degrees}) field-based misalignment adequately. Our novel hyperspectral imaging method is adapted for field conditions and opens up novel opportunities for capturing the complex and dynamic nature of the light environment.

systems biology↗

bioRxiv2021

Luminosity thresholds of colored surfaces are determined by their heuristic upper-limit luminances in the visual system

We typically have a fairly good idea whether a given object is self-luminous or illuminated, but it is not fully understood how we make this judgement. This study aimed to identify determinants of the luminosity threshold, a luminance level at which a surface begins to appear self-luminous. We specifically tested a hypothesis that our visual system knows the maximum luminance level that a surface can reach under the physical constraint that a surface cannot reflect more light than any incident light and applies this prior to determine the luminosity thresholds. Observers were presented with a 2-degree circular test field surrounded by numerous overlapping colored circles and luminosity thresholds were measured as a function of (i) the chromaticity of the test field, (ii) the shape of surrounding color distribution and (iii) the color of the illuminant of the surrounding colors. We found that the luminosity thresholds peaked around the chromaticity of test illuminants and decreased as the purity of the test chromaticity increased. However, the loci of luminosity thresholds across chromaticities were nearly invariant to the shape of the surrounding color distribution and generally resembled the loci drawn from theoretical upper-limit luminances and upper-limit luminance boundaries of real objects. These trends were particularly evident for illuminants on the black-body locus and did not hold well under atypical illuminants such as magenta or green. These results support the idea that our visual system empirically internalizes the gamut of surface colors under natural illuminants and a given object appears self-luminous when its luminance exceeds this internalized upper-limit luminance.

neuroscience↗

bioRxiv2021

Nasal delivery of single-domain antibodies improve symptoms of SARS-CoV-2 infection in an animal model

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the disease COVID-19 can lead to serious symptoms, such as severe pneumonia, in the elderly and those with underlying medical conditions. While vaccines are now available, they do not work for everyone and therapeutic drugs are still needed particularly for treating life-threatening conditions. Here, we showed nasal delivery of a new, unmodified camelid single-domain antibody (VHH), termed K-874A, effectively inhibited SARS-CoV-2 titers in infected lungs of Syrian hamsters without causing weight loss and cytokine induction. In vitro studies demonstrated that K-874A neutralized SARS-CoV-2 in both VeroE6/TMPRSS2 and human lung-derived alveolar organoid cells. Unlike other drug candidates, K-874A blocks viral membrane fusion rather than viral attachment. Cryo-electron microscopy revealed K-874A bound between the receptor binding domain and N-terminal domain of the virus S protein. Further, infected cells treated with K-874A produced fewer virus progeny that were less infective. We propose that direct administration of K-874A to the lung via a nebulizer could be a new treatment for preventing the reinfection of amplified virus in COVID-19 patients. Author summaryVaccines for COVID-19 are now available but therapeutic drugs are still needed to treat life-threatening cases and those who cannot be vaccinated. We discovered a new heavy-chain single-domain antibody that can effectively neutralize the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes COVID-19. Unlike other drug candidates, which prevent the virus from attaching to the receptor on the host cell, this new antibody acts by blocking the virus membrane from fusing with the host cell membrane. We studied the behavior of the new antibody in vitro using VeroE6/TMPRSS2 cells and human lung organoids. When delivered through the nose to infected Syrian hamsters, we found that this antibody could prevent the typical symptoms caused by SARS-CoV-2. Our results are significant because delivering simple drugs directly to infected lungs using a nebulizer could increase the potency of the drugs while reducing the risk of immune reaction that could occur if the drugs escape or are delivered through the blood stream.

microbiology↗

bioRxiv2021

Beyond colour gamuts: Novel metrics for thereproduction of photoreceptor signals

Colour gamuts describe the chromaticity reproduction capabilities of a display, i.e. its ability to reproduce the relative cone excitations from real-world radiance spectra. While the cones dominate "canonical" visual function (i.e. perception of colour, space, and motion) under photopic light levels, they are not the only photoreceptors in the human retina. Rods and melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) also respond to light and contribute to both visual and non-visual light responses, including circadian rhythms, sleep-wake control, mood, pupil size, and alertness. Three-primary display technologies, with their focus on reproducing colour, are not designed to reproduce the rod and melanopsin excitations. Moreover, conventional display metrics used to characterize three-primary displays fail to describe the displays ability (or inability) to reproduce rod and melanopsin excitations, and thus do not capture the displays ability to reproduce the full human physiological response to light. In this paper, three novel physiologically relevant metrics are proposed for quantifying the reproduction and distortion of the photoreceptor signals by visual displays. A novel equal-luminance photoreceptor excitation diagram is proposed, extending the well-known MacLeod-Boynton chromaticity diagram, to allow visualizations of the five-dimensional photoreceptor signal space in a three-dimensional projection.

neuroscience↗

bioRxiv2020

Explaining #TheShoe based on the optimal color hypothesis: The role of chromaticity vs. luminance distribution in ambiguous image

The image of #theShoe is a derivative image of #theDress which induced vastly different color experiences across individuals. The majority of people perceive that the shoe has grey leather with turquoise laces, but others report pink leather with white laces. We hypothesized #theShoe presents the problem of color constancy, where different people estimated different illuminants falling onto the shoe. The present study specifically aimed to understand what cues in the shoe image caused the ambiguity based on the optimal color hypothesis: our visual system knows the gamut of surface colors under various illuminants and applies the knowledge for illuminant estimation. The analysis showed that estimated illuminant chromaticity largely changes depending on the assumed intensity of the illuminant. When the illuminant intensity was assumed to be low, a high color temperature was estimated. In contrast, assuming high illuminant intensity led to the estimation of low color temperature. A simulation based on a von Kries correction showed that the subtraction of estimated illuminants from the original image shifts the appearance of the shoe towards the reported states (i.e. gray-turquoise or pink-white). These results suggest that the optimal color hypothesis provides a theoretical interpretation to the #theShoe phenomenon. Moreover, this luminance-dependent color-shift was observed in #theDress phenomenon, supporting the notion that the same trigger induced #theShoe.

neuroscience↗

bioRxiv2020

Color constancy based on the geometry of color distribution

A white surface appears white under different lighting environments. This ability is referred to color constancy. The physical inputs to our visual system are dictated by the interplay between lights and surfaces, and thus for the surface color to be stably perceived, the illuminant influence needs to be discounted. To reveal our strategy to infer the illuminant color, we conducted three psychophysical experiments designed to test optimal color hypothesis: we internalize the physical color gamut under a particular illuminant and apply the prior to estimate the illuminant color. In each experiment, we presented 61 hexagons arranged without spatial gaps, where the surrounding 60 hexagons were set to have a specific shape in their color distribution. We asked participants to adjust the color of a center test field so that it appears a full-white surface placed under a test illuminant. Results and computational modeling suggested that although our proposed model is limited in accounting for estimation of illuminant intensity by human observers, it agrees fairly well with the estimates of illuminant chromaticity in most tested conditions. The accuracy of estimation generally outperformed other tested conventional color constancy models. These results support the hypothesis that our visual system can utilize the geometry of scene color distribution to achieve color constancy.

neuroscience↗

bioRxiv2020

Arabidopsis SMN2/HEN2, encoding DEAD-box RNA helicase, governs proper expression of the resistance gene SMN1/RPS6 and is involved in dwarf, autoimmune phenotypes of mekk1 and mpk4

In Arabidopsis thaliana, a mitogen-activated protein kinase pathway, MEKK1-MKK1/MKK2-MPK4, is important for basal resistance, and disruption of this pathway results in dwarf, autoimmune phenotypes. To elucidate the complex mechanisms activated by the disruption of this pathway, we have previously developed a mutant screening system based on a dwarf autoimmune line that overexpressed the N-terminal regulatory domain of MEKK1. Here, we report that the second group of mutants, smn2, had defects in the SMN2 gene, encoding a DEAD-box RNA helicase. SMN2 is identical to HEN2, whose function is vital for the nuclear RNA exosome because it provides non-ribosomal RNA specificity for RNA turnover, RNA quality control, and RNA processing. Aberrant SMN1/RPS6 transcripts were detected in smn2 and hen2 mutants. Disease resistance against Pseudomonas syringae pv. tomato DC3000 (hopA1), which is conferred by SMN1/RPS6, was decreased in smn2 mutants, suggesting a functional connection between SMN1/RPS6 and SMN2/HEN2. We produced double mutants mekk1smn2 and mpk4smn2 to determine whether the smn2 mutations suppress the dwarf, autoimmune phenotypes of the mekk1 and mpk4 mutants, as the smn1 mutations do. As expected, the mekk1 and mpk4 phenotypes were suppressed by the smn2 mutations. These results suggested that SMN2 is involved in proper function of SMN1/RPS6. The GO enrichment analysis using RNA-seq data showed that defense genes were downregulated in smn2, suggesting positive contribution of SMN2 to genome-wide expression of defense-related genes. In conclusion, this study provides novel insight into plant immunity via SMN2/HEN2, an essential component of the nuclear RNA exosome.

plant biology↗

bioRxiv2019

Hyperspectral environmental illumination maps: Characterizing directional spectral variation in natural environments

Objects placed in real-world scenes receive incident light from every direction, and the spectral content of this light may vary from one direction to another. In computer graphics, environmental illumination is approximated using maps that specify illumination at a point as a function of incident angle. However, to-date, existing public databases of environmental illumination maps specify only three colour channels (RGB). We have captured a new set of 12 environmental illumination maps (eight outdoor scenes; four indoor scenes) using a hyperspectral imaging system with 33 spectral channels. The data reveal a striking directional variation of spectral distribution of lighting in natural environments. We discuss limitations of using daylight models to describe natural environmental illumination.

neuroscience↗