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- Evans Blue as a Simple Method to Discriminate Mosquitoes' Feeding Choice on Small Laboratory Animals. [JOURNAL ARTICLE]
- PLoS One 2014; 9(10):e110551.
Temperature, humidity, vision, and particularly odor, are external cues that play essential roles to mosquito blood feeding and oviposition. Entomological and behavioral studies employ well-established methods to evaluate mosquito attraction or repellency and to identify the source of the blood meal. Despite the efficacy of such methods, the costs involved in the production or acquisition of all parts, components and the chemical reagents involved are unaffordable for most researchers from poor countries. Thus, a simple and relatively low-cost method capable of evaluating mosquito preferences and the blood volume ingested is desirable.By using Evans blue (EB) vital dye and few standard laboratory supplies, we developed and validated a system capable of evaluating mosquito's choice between two different host sources of blood. EB-injected and PBS-injected mice submitted to a number of situations were placed side by side on the top of a rounded recipient covered with tulle fabric and containing Aedes aegypti mosquitoes. Homogenates from engorged mosquitoes clearly revealed the blood source (EB- or PBS-injected host), either visually or spectrometrically. This method was able to estimate the number of engorded mosquitoes, the volume of blood ingested, the efficacy of a commercial repellent and the attractant effects of black color and human sweat.Despite the obvious limitations due to its simplicity and to the dependence of a live source of blood, the present method can be used to assess a number of host variables (diet, aging, immunity, etc) and optimized for several aspects of mosquito blood feeding and vector-host interactions. Thus, it is proposed as an alternative to field studies, and it could be used for initial screenings of chemical compound candidates for repellents or attractants, since it replicates natural conditions of exposure to mosquitoes in a laboratory environment.
- Protan Response Times to Red Lights in a Mildly Hypoxic Environment. [JOURNAL ARTICLE]
- Aviat Space Environ Med 2014 Nov; 85(11):1078-1085.
Hovis JK, Milburn NJ, Nesthus TE. Protan response times to red lights in a mildly hypoxic environment. Aviat Space Environ Med 2014; 85:1078-85.This study was conducted to determine whether protans have slower reaction times to red lights than individuals with normal color vision and to identify whether protan reaction times increase differentially in a mildly hypoxic environment.Simple reaction times (SRT) to a red light-emitting diode (LED) display were measured using the Psychomotor Vigilance Task (PVT) at ground (1293 ft/394 m), simulated 12,400-ft (3780-m) altitude, and 20 min after returning to ground. Subjects were 13 individuals with normal color vision (NCV), 12 with a deutan color vision defect, and 4 with a protan color vision defect.The mean reaction times increased by 8% with altitude and decreased after returning to ground for all groups. However, the reaction times of the protans were often faster than the NCV mean and never below the NCV 10(th) percentile. The only significant difference between color vision groups was the slowest mean reaction time of the NCV group was slower than both the pooled dichromats and pooled anomalous trichromats across all conditions by 23%. The number of lapses did not vary with altitude, but the dichromatic subjects had significantly fewer lapses than the trichromatic subjects across all conditions.Although protans may be slower to respond to some red warning lights, this decrement in performance could not be demonstrated under the conditions of our experiment. Furthermore, the protan group's simple reaction times were not differentially affected by mild hypoxia. These results suggest that the red LEDs were sufficiently bright for these protan observers.
- Spectral and spatial selectivity of luminance vision in reef fish. [Journal Article]
- Front Neural Circuits 2014.:118.
Luminance vision has high spatial resolution and is used for form vision and texture discrimination. In humans, birds and bees luminance channel is spectrally selective-it depends on the signals of the long-wavelength sensitive photoreceptors (bees) or on the sum of long- and middle-wavelength sensitive cones (humans), but not on the signal of the short-wavelength sensitive (blue) photoreceptors. The reasons of such selectivity are not fully understood. The aim of this study is to reveal the inputs of cone signals to high resolution luminance vision in reef fish. Sixteen freshly caught damselfish, Pomacentrus amboinensis, were trained to discriminate stimuli differing either in their color or in their fine patterns (stripes vs. cheques). Three colors ("bright green", "dark green" and "blue") were used to create two sets of color and two sets of pattern stimuli. The "bright green" and "dark green" were similar in their chromatic properties for fish, but differed in their lightness; the "dark green" differed from "blue" in the signal for the blue cone, but yielded similar signals in the long-wavelength and middle-wavelength cones. Fish easily learned to discriminate "bright green" from "dark green" and "dark green" from "blue" stimuli. Fish also could discriminate the fine patterns created from "dark green" and "bright green". However, fish failed to discriminate fine patterns created from "blue" and "dark green" colors, i.e., the colors that provided contrast for the blue-sensitive photoreceptor, but not for the long-wavelength sensitive one. High resolution luminance vision in damselfish, Pomacentrus amboinensis, does not have input from the blue-sensitive cone, which may indicate that the spectral selectivity of luminance channel is a general feature of visual processing in both aquatic and terrestrial animals.
- Prior Knowledge about Objects Determines Neural Color Representation in Human Visual Cortex. [JOURNAL ARTICLE]
- Cereb Cortex 2014 Oct 16.
To create subjective experience, our brain must translate physical stimulus input by incorporating prior knowledge and expectations. For example, we perceive color and not wavelength information, and this in part depends on our past experience with colored objects ( Hansen et al. 2006; Mitterer and de Ruiter 2008). Here, we investigated the influence of object knowledge on the neural substrates underlying subjective color vision. In a functional magnetic resonance imaging experiment, human subjects viewed a color that lay midway between red and green (ambiguous with respect to its distance from red and green) presented on either typical red (e.g., tomato), typical green (e.g., clover), or semantically meaningless (nonsense) objects. Using decoding techniques, we could predict whether subjects viewed the ambiguous color on typical red or typical green objects based on the neural response of veridical red and green. This shift of neural response for the ambiguous color did not occur for nonsense objects. The modulation of neural responses was observed in visual areas (V3, V4, VO1, lateral occipital complex) involved in color and object processing, as well as frontal areas. This demonstrates that object memory influences wavelength information relatively early in the human visual system to produce subjective color vision.
- Substance specific chemical sensing with pristine and modified photonic nanoarchitectures occurring in blue butterfly wing scales. [Journal Article]
- Opt Express 2014 Sep 22; 22(19):22649-60.
Butterfly wing scales containing photonic nanoarchitectures act as chemically selective sensors due to their color change when mixing vapors in the atmosphere. Based on butterfly vision, we built a model for efficient characterization of the spectral changes in different atmospheres. The spectral shift is vapor specific and proportional with the vapor concentration. Results were compared to standard principal component analysis. The modification of the chemical properties of the scale surface by the deposition of 5 nm of Al<sub>2</sub>O<sub>3</sub> significantly alters the character of the optical response. This is proof of the possibility to purposefully tune the selectivity of such sensors.
- Arbitrary cylinder color model for the codebook based background subtraction. [Journal Article]
- Opt Express 2014 Sep 8; 22(18):21577-88.
The codebook background subtraction approach is widely used in computer vision applications. One of its distinguished features is the cylinder color model used to cope with illumination changes. The performances of this approach depends strongly on the color model. However, we have found this color model is valid only if the spectrum components of the light source change in the same proportion. In fact, this is not true in many practical cases. In these cases, the performances of the approach would be degraded significantly. To tackle this problem, we propose an arbitrary cylinder color model with a highly efficient updating strategy. This model uses cylinders whose axes need not going through the origin, so that the cylinder color model is extended to much more general cases. Experimental results show that, with no loss of real-time performance, the proposed model reduces the wrong classification rate of the cylinder color model by more than fifty percent.
- Dichromatic vision in a fruit bat with diurnal proclivities: the Samoan flying fox (Pteropus samoensis). [JOURNAL ARTICLE]
- J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2014 Oct 16.
A nocturnal bottleneck during mammalian evolution left a majority of species with two cone opsins, or dichromatic color vision. Primate trichromatic vision arose from the duplication and divergence of an X-linked opsin gene, and is long attributed to tandem shifts from nocturnality to diurnality and from insectivory to frugivory. Opsin gene variation and at least one duplication event exist in the order Chiroptera, suggesting that trichromatic vision could evolve under favorable ecological conditions. The natural history of the Samoan flying fox (Pteropus samoensis) meets these conditions-it is a large bat that consumes nectar and fruit and demonstrates strong diurnal proclivities. It also possesses a visual system that is strikingly similar to that of primates. To explore the potential for opsin gene duplication and divergence in this species, we sequenced the opsin genes of 11 individuals (19 X-chromosomes) from three South Pacific islands. Our results indicate the uniform presence of two opsins with predicted peak sensitivities of ca. 360 and 553 nm. This result fails to support a causal link between diurnal frugivory and trichromatic vision, although it remains plausible that the diurnal activities of P. samoensis have insufficient antiquity to favor opsin gene renovation.
- How the venetian blind percept emerges from the laminar cortical dynamics of 3D vision. [Journal Article]
- Front Psychol 2014.:694.
The 3D LAMINART model of 3D vision and figure-ground perception is used to explain and simulate a key example of the Venetian blind effect and to show how it is related to other well-known perceptual phenomena such as Panum's limiting case. The model proposes how lateral geniculate nucleus (LGN) and hierarchically organized laminar circuits in cortical areas V1, V2, and V4 interact to control processes of 3D boundary formation and surface filling-in that simulate many properties of 3D vision percepts, notably consciously seen surface percepts, which are predicted to arise when filled-in surface representations are integrated into surface-shroud resonances between visual and parietal cortex. Interactions between layers 4, 3B, and 2/3 in V1 and V2 carry out stereopsis and 3D boundary formation. Both binocular and monocular information combine to form 3D boundary and surface representations. Surface contour surface-to-boundary feedback from V2 thin stripes to V2 pale stripes combines computationally complementary boundary and surface formation properties, leading to a single consistent percept, while also eliminating redundant 3D boundaries, and triggering figure-ground perception. False binocular boundary matches are eliminated by Gestalt grouping properties during boundary formation. In particular, a disparity filter, which helps to solve the Correspondence Problem by eliminating false matches, is predicted to be realized as part of the boundary grouping process in layer 2/3 of cortical area V2. The model has been used to simulate the consciously seen 3D surface percepts in 18 psychophysical experiments. These percepts include the Venetian blind effect, Panum's limiting case, contrast variations of dichoptic masking and the correspondence problem, the effect of interocular contrast differences on stereoacuity, stereopsis with polarity-reversed stereograms, da Vinci stereopsis, and perceptual closure. These model mechanisms have also simulated properties of 3D neon color spreading, binocular rivalry, 3D Necker cube, and many examples of 3D figure-ground separation.
- Asymmetric effects of luminance and chrominance in the watercolor illusion. [Journal Article]
- Front Hum Neurosci 2014.:723.
When bounded by a line of sufficient contrast, the desaturated hue of a colored line will spread over an enclosed area, an effect known as the watercolor illusion. The contrast of the two lines can be in luminance, chromaticity, or a combination of both. The effect is most salient when the enclosing line has greater contrast with the background than the line that induces the spreading color. In most prior experiments with watercolor spreading, the luminance of both lines has been lower than the background. An achromatic version of the illusion exists where a dark line will spread while being bounded by either a darker or brighter line. In a previous study we measured the strength of the watercolor effect in which the colored inducing line was isoluminant to the background, and found an illusion for both brighter and darker achromatic outer contours. We also found the strength of spreading is stronger for bluish (+S cone input) colors compared to yellowish (-S cone input) ones, when bounded by a dark line. The current study set out to measure the hue dependence of the watercolor illusion when inducing colors are flanked with brighter (increment) as opposed to darker outer lines. The asymmetry in the watercolor effect with S cone input was enhanced when the inducing contrast was an increment rather than a decrement. Further experiments explored the relationship between the perceived contrast of these chromatic lines when paired with luminance increments and decrements and revealed that the perceived contrast of luminance increments and decrements is dependent on which isoluminant color they are paired with. In addition to known hue asymmetries in the watercolor illusion there are asymmetries between luminance increments and decrements that are also hue dependent. These latter asymmetries may be related to the perceived contrast of the hue/luminance parings.
- Light eyes, drugs and the sun: a bad mix. [News]
- Johns Hopkins Med Lett Health After 50 2014 Aug; 26(7):8.