Polymorphism in red photopigment underlies variation in colour matching.

Genetic variation of human senses within the normal range probably exists but usually cannot be investigated in detail for lack of appropriate methods. The study of subtle perceptual differences in red-green colour vision is feasible since both photopigment genotypes and psychophysical phenotypes can be assessed by sophisticated techniques. Red-green colour vision in humans is mediated by two different visual pigments: red (long-wavelength sensitive) and green (middle-wavelength sensitive). The apoproteins of these highly homologous photopigments are encoded by genes on the X chromosome. Colour matches of males with normal colour vision fall into two main groups that appear to be transmitted by X-linked inheritance. This difference in colour matching is likely to reflect small variations in the absorption maxima of visual pigments, suggesting the presence of two common variants of the red and/or green visual pigments that differ in spectral positioning. We report that a common single amino-acid polymorphism (62% Ser, 38% Ala) at residue 180 of the X-linked red visual pigment explains the finding of two major groups in the distribution of colour matching among males with normal colour vision.     

Sensory adaptation. Tunable colour vision in a mantis shrimp

Systems of colour vision are normally identical in all members of a species, but a single design may not be adequate for species living in a diverse range of light environments. Here we show that in the mantis shrimp Haptosquilla trispinosa, which occupies a range of depths in the ocean, long-wavelength colour receptors are individually tuned to the local light environment. The spectral sensitivity of specific classes of photoreceptor is adjusted by filters that vary between individuals.     

Scotopic colour vision in nocturnal hawkmoths

Humans are colour-blind at night, and it has been assumed that this is true of all animals. But colour vision is as useful for discriminating objects at night as it is during the day. Here we show, through behavioural experiments, that the nocturnal hawkmoth Deilephila elpenor uses colour vision to discriminate coloured stimuli at intensities corresponding to dim starlight (0.0001 cd x m(-2)). It can do this even if the illumination colour changes, thereby showing colour constancy-a property of true colour vision systems. In identical conditions humans are completely colour-blind. Our calculations show that the possession of three photoreceptor classes reduces the absolute sensitivity of the eye, which indicates that colour vision has a high ecological relevance in nocturnal moths. In addition, the photoreceptors of a single ommatidium absorb too few photons for reliable discrimination, indicating that spatial and/or temporal summation must occur for colour vision to be possible. Taken together, our results show that colour vision occurs at nocturnal intensities in a biologically relevant context.     

The arrangement of the three cone classes in the living human eye

Human colour vision depends on three classes of receptor, the short- (S), medium- (M), and long- (L) wavelength-sensitive cones. These cone classes are interleaved in a single mosaic so that, at each point in the retina, only a single class of cone samples the retinal image. As a consequence, observers with normal trichromatic colour vision are necessarily colour blind on a local spatial scale. The limits this places on vision depend on the relative numbers and arrangement of cones. Although the topography of human S cones is known, the human L- and M-cone submosaics have resisted analysis. Adaptive optics, a technique used to overcome blur in ground-based telescopes, can also overcome blur in the eye, allowing the sharpest images ever taken of the living retina. Here we combine adaptive optics and retinal densitometry to obtain what are, to our knowledge, the first images of the arrangement of S, M and L cones in the living human eye. The proportion of L to M cones is strikingly different in two male subjects, each of whom has normal colour vision. The mosaics of both subjects have large patches in which either M or L cones are missing. This arrangement reduces the eye's ability to recover colour variations of high spatial frequency in the environment but may improve the recovery of luminance variations of high spatial frequency.     

Changes in colour appearance following post-receptoral adaptation

Current models of colour vision assume that colour is represented by activity in three independent post-receptoral channels: two encoding chromatic information and one encoding luminance. An important feature of these models is that variations in certain directions in colour space modulate the response of only one of the channels. We have tested whether such models can predict how colour appearance is altered by adaptation-induced changes in post-receptoral sensitivity. In contrast to the changes predicted by three independent channels, colour appearance is always distorted away from the direction in colour space to which the observer has adapted. This suggests that at the level at which the adaptation effects occur, there is no colour direction that invariably isolates only a single post-receptoral channel.     

Ecological importance of trichromatic vision to primates

Trichromatic colour vision, characterized by three retinal photopigments tuned to peak wavelengths of approximately 430 nm, approximately 535 nm and approximately 562 nm (refs 1, 2), has evolved convergently in catarrhine primates and one genus of New World monkey, the howlers (genus Alouatta). This uniform capacity to discriminate red-green colours, which is not found in other mammals, has been proposed as advantageous for the long-range detection of either ripe fruits or young leaves (which frequently flush red in the tropics) against a background of mature foliage. Here we show that four trichromatic primate species in Kibale Forest, Uganda, eat leaves that are colour discriminated only by red-greenness, a colour axis correlated with high protein levels and low toughness. Despite their divergent digestive systems, these primates have no significant interspecific differences in leaf colour selection. In contrast, eaten fruits were generally discriminated from mature leaves on both red-green and yellow-blue channels and also by their luminance, with a significant difference between chimpanzees and monkeys in fruit colour choice. Our results implicate leaf consumption, a critical food resource when fruit is scarce, as having unique value in maintaining trichromacy in catarrhines.     

Polymorphism of the long-wavelength cone in normal human colour vision

Colour vision is based on the presence of multiple classes of cone each of which contains a different type of photopigment. Colour matching tests have long revealed that the normal human has three cone types. Results from these tests have also been used to provide estimates of cone spectral sensitivities. There are significant variations in colour matches made by individuals whose colour vision is classified as normal. Some of this is due to individual differences in preretinal absorption and photopigment density, but some is also believed to arise because there is variation in the spectral positioning of the cone pigments among those who have normal colour vision. We have used a sensitive colour matching test to examine the magnitude and nature of this individual variation and here report evidence for the existence of two different long-wavelength cone mechanisms in normal humans. The different patterns of colour matches made by male and female subjects indicate these two mechanisms are inherited as an X-chromosome linked trait.     

两种基于高双折射光纤环的高阶超精细梳状滤波器

设计了两种基于高双折射(HiBi)光纤萨尼亚克环的可调谐高阶超精细梳状滤波器,其由偏振控制器(PC)、环形器、2段(或3段)Hi Bi保偏光纤(PMF)组成,具有单输入双输出和高阶超精细梳状光谱的特性,调谐灵活、输出光谱精细等特点.建立了理论模型研究光谱的双输出特性;对二阶滤波器,仿真研究了在Hi Bi光纤长度相等时偏振角度对输出梳状光谱的影响;对三阶滤波器,仿真研究了的Hi Bi光纤长度对输出梳状光谱的影响.结果表明该种高阶滤波器可应用于不同波长光波的选频输出.     

Effect on eye development of dominant mutations in Drosophila homologue of the EGF receptor

The compound eye of the adult fruitfly, Drosophila melanogaster, comprises about 800 identical ommatidia, or unit eyes, each containing 20 distinct cells. We have used histological and immunocytochemical methods to study the development of the compound eye in Ellipse (Elp) mutants. In Elp/Elp, most ommatidia do not initiate differentiation. We present genetic evidence that Elp alleles are mutations of the Drosophila homologue of the epidermal growth factor (EGF) receptor, and suggest that activity of the EGF receptor may determine the spacing pattern of ommatidia in the eye.     

Parallel processing of motion and colour information

When the two eyes are confronted with sufficiently different versions of the visual environment, one or the other eye dominates perception in alternation. A similar situation may be created in the laboratory by presenting images to the left and right eyes which differ in orientation or colour. Although perception is dominated by one eye during rivalry, there are a number of instances in which visual processes nevertheless continue to integrate information from the suppressed eye. For example the interocular transfer of the motion after-effect is undiminished when induced during binocular rivalry. Thus motion information processing may occur in parallel with the rivalry process. Here we describe a novel example in which the visual system simultaneously exhibits binocular rivalry and vision that integrates signals from both eyes. This apparent contradiction is resolved by postulating parallel visual processes devoted to the analyses of colour and motion information. Counterphased gratings are viewed dichoptically such that for one eye the grating is composed of alternating yellow and black stripes (luminance) while for the other it is composed of alternating red and green stripes (chrominance). When the gratings are fused, a moving grating is perceived. A consistent direction of motion can only be achieved if left and right monocular signals are integrated by the nervous system. Yet the apparent colour of the binocular percept alternates between red-green and yellow-black. These observations demonstrate the segregation of processing by the early motion system from that affording the perception of colour. Although, in this stimulus, colour information in itself can play no part in the cyclopean perception of motion direction, colour is carried along perceptually (filled in) by the moving pattern which is integrated from both eyes.     

Chromatic sensitivity of ganglion cells in the peripheral primate retina

Visual abilities change over the visual field. For example, our ability to detect movement is better in peripheral vision than in foveal vision, but colour discrimination is markedly worse. The deterioration of colour vision has been attributed to reduced colour specificity in cells of the midget, parvocellular (PC) visual pathway in the peripheral retina. We have measured the colour specificity (red-green chromatic modulation sensitivity) of PC cells at eccentricities between 20 and 50 degrees in the macaque retina. Here we show that most peripheral PC cells have red-green modulation sensitivity close to that of foveal PC cells. This result is incompatible with the view that PC pathway cells in peripheral retina make indiscriminate connections ('random wiring') with retinal circuits devoted to different spectral types of cone photoreceptors. We show that selective cone connections can be maintained by dendritic field anisotropy, consistent with the morphology of PC cell dendritic fields in peripheral retina. Our results also imply that postretinal mechanisms contribute to the psychophysically demonstrated deterioration of colour discrimination in the peripheral visual field.     

The colour centre in the cerebral cortex of man

Anatomical and physiological studies have shown that there is an area specialized for the processing of colour (area V4) in the prestriate cortex of macaque monkey brain. Earlier this century, suggestive clinical evidence for a colour centre in the brain of man was dismissed because of the association of other visual defects with the defects in colour vision. However, since the demonstration of functional specialization in the macaque cortex, the question of a colour centre in man has been reinvestigated, based on patients with similar lesions in the visual cortex. In order to study the colour centre in normal human subjects, we used the technique of positron emission tomography (PET), which measures increases in blood flow resulting from increased activity in the cerebral cortex. A comparison of the results of PET scans of subjects viewing multi-coloured and black-and-white displays has identified a region of normal human cerebral cortex specialized for colour vision.     

Is colour vision possible with only rods and blue-sensitive cones?

At night all cats are grey, but with the approach of dawn they take on colour. By starlight, a single class of photoreceptors, the rods, function, whereas by daylight, three classes, the blue-, green- and red-sensitive cones, are active and provide colour vision. Only by comparing the rates of quantal absorption in more than one photoreceptor class is colour vision possible. Although the comparisons generally take place between the cones, they can involve the rods as well. Here we investigate the wavelength discrimination of an extremely rare group of individuals, blue-cone monochromats, who have only rods and one class of cones. We find that these individuals can distinguish wavelengths (440 to 500 nm) in the twilight region where the rods and blue-sensitive cones are simultaneously active.     

Ultraviolet vision in a bat

Most mammals, with the exception of primates, have dichromatic vision and correspondingly limited colour perception. Ultraviolet vision was discovered in mammals only a decade ago, and in the few rodents and marsupials where it has been found, ultraviolet light is detected by an independent photoreceptor. Bats orient primarily by echolocation, but they also use vision. Here we show that a phyllostomid flower bat, Glossophaga soricina, is colour-blind but sensitive to ultraviolet light down to a wavelength of 310 nm. Behavioural experiments revealed a spectral-sensitivity function with maxima at 510 nm (green) and above 365 nm (ultraviolet). A test for colour vision was negative. Chromatic adaptation had the same threshold-elevating effects on ultraviolet and visible test lights, indicating that the same photoreceptor is responsible for both response peaks (ultraviolet and green). Thus, excitation of the beta-band of the visual pigment is the most likely cause of ultraviolet sensitivity. This is a mechanism for ultraviolet vision that has not previously been demonstrated in intact mammalian visual systems.     

Spatial structure of cone inputs to receptive fields in primate lateral geniculate nucleus.

Human colour vision depends on three classes of cone photoreceptors, those sensitive to short (S), medium (M) or long (L) wavelengths, and on how signals from these cones are combined by neurons in the retina and brain. Macaque monkey colour vision is similar to human, and the receptive fields of macaque visual neurons have been used as an animal model of human colour processing. P retinal ganglion cells and parvocellular neurons are colour-selective neurons in macaque retina and lateral geniculate nucleus. Interactions between cone signals feeding into these neurons are still unclear. On the basis of experimental results with chromatic adaptation, excitatory and inhibitory inputs from L and M cones onto P cells (and parvocellular neurons) were thought to be quite specific (Fig. 1a). But these experiments with spatially diffuse adaptation did not rule out the 'mixed-surround' hypothesis: that there might be one cone-specific mechanism, the receptive field centre, and a surround mechanism connected to all cone types indiscriminately (Fig. 1e). Recent work has tended to support the mixed-surround hypothesis. We report here the development of new stimuli to measure spatial maps of the linear L-, M- and S-cone inputs to test the hypothesis definitively. Our measurements contradict the mixed-surround hypothesis and imply cone specificity in both centre and surround.     

筒子在筒子架不同位置上对片纱整经张力影响的分析和探讨

本文分析和探讨了筒子在筒子架不同位置上对片纱整经张力的影响问题,提出了与传统观点不同的新见解,指出该影响主要发生在片纱形成区,其变化规律随整经形式(分批、分条整经)、穿筘方法(分排法与分层法)以及整经机尺寸参数而变化.在相同初张力条件下,在筒子架区域内,前后排张力差异甚微.文章对分排法穿筘优于分层法作了新的解释,并指出分段分层加压措施在生产实际中往往难以精确确定加压原则和加压差异量,建议采用等加压型式的筒子架.     

糠虾复眼的形态发育

采用扫描电镜技术研究了糠虾(Mysis latreille)无节幼体到成体复眼的形态发育，结果显示幼体期复眼的发育还不完善，组成复眼的小眼仅为圆形的泡状浅突，相互间距大．组成糠虾成体复眼的小眼数量约为600个，小眼面为典型的正六边形，仅在复眼与眼柄交界处有四边形和五边形的小眼．复眼的增大在幼体期主要是由于小眼表面积增大引起的，在仔虾期后主要是由于小眼数量增多引起的．     

一种两级CMOS运算放大器电源抑制比提高技术

在解释了传统基本两级CMOS运算放大器低电源抑制比(PSRR)原因的基础上,提出了一种简单电路技术来提高传统基本两级CMOS运算放大器中频PSRR.该方法原理是通过改变偏置结构产生一个额外的信号支路在输出端跟随电源增益,这样在输出端可以得到近似为零的电源纹波增益,从而能提高运放的PSRR.采用0.35μm标准CMOS工艺库,在Cadence环境下仿真结果显示,改进的运算放大器的PSRR在中频范围内比传统运算放大器可提高20 dB以上.