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PubMed2005

Generalization and categorization of spectral colors in goldfish I. Experiments with one training wavelength.

Goldfish have a tetrachromatic color vision with a high discrimination ability for spectral colors as well as for object colors. We investigate the question whether goldfish organize the high number of discriminable colors in terms of color categories, i.e. in a few larger groups of colors independent of wavelength discrimination. Twenty-four goldfish were trained with food reward, each fish on one out of 13 wavelengths between 371 nm and 630 nm. In transfer tests two different wavelengths were presented, one shorter and one longer than the training wavelength, and the choice behavior was determined. Choice frequencies of >or=50% were assumed to indicate similarity to the training color. The wavelength ranges >or=50% were about 100 nm and twice as large as the just noticeable differences measured in wavelength discrimination tests (Fig. 7). The ranges were surprisingly about the same for all training wavelengths, provided the data were plotted on a wavelength scale weighted according to discrimination ability (Fig. 4). Thus, with the training method chosen goldfish showed a kind of categorization which, however, depends on training wavelength and discrimination ability. Generalization tests in which training wavelength and test wavelengths were shown separately for 2 min each gave the same results as wavelength discrimination tests (Figs. 5 and 6) and are, therefore, not indicative for color categories.

Animals↗
PubMedDate not supplied

Vision impairment and driving.

Driving is the primary mode of travel in many countries. It facilitates the performance of routine daily activities and is thus integral with the concept of quality of life. Vision is inarguably a fundamental component of safe driving. Drivers with certain eye conditions reduce their driving exposure and restrict their driving to the safest times, yet there is preliminary evidence that some eye conditions increase the risk of crashes. Visual acuity is only weakly related to crash involvement, whereas peripheral vision appears to play a more critical role. Color vision deficiency by itself is not a threat to safe driving. Based on the current literature, it is unclear whether other types of visual sensory impairment have a significant impact on driving safety and performance. Tests of visual attention and processing speed show great promise as methods of identifying high-risk drivers. There is a serious need for well-designed studies in key practical areas, such as the safety of low-vision drivers who use bioptic telescopes, the impact of monocular vision impairment on safety, and the effectiveness of vision rescreening policies after initial licensure. For ophthalmologists to guide patients about driving fitness, valid and reliable assessment tools must be developed and made widely available.

Accidents, Traffic↗
PubMed1986

Evaluation of linear models of surface spectral reflectance with small numbers of parameters.

Recent computational models of color vision demonstrate that it is possible to achieve exact color constancy over a limited range of lights and surfaces described by linear models. The success of these computational models hinges on whether any sizable range of surface spectral reflectances can be described by a linear model with about three parameters. In the first part of this paper, I analyze two large sets of empirical surface spectral reflectances and examine three conjectures concerning constraints on surface reflectance: that empirical surface reflectances fall within a linear model with a small number of parameters, that empirical surface reflectances fall within a linear model composed of band-limited functions with a small number of parameters, and that the shape of the spectral-sensitivity curves of human vision enhance the fit between empirical surface reflectances and a linear model. I conclude that the first and second conjectures hold for the two sets of spectral reflectances analyzed but that the number of parameters required to model the spectral reflectances is five to seven, not three. A reanalysis of the empirical data that takes human visual sensitivity into account gives more promising results. The linear models derived provide excellent fits to the data with as few as three or four parameters, confirming the third conjecture. The results suggest that constraints on possible surface-reflectance functions and the "filtering" properties of the shapes of the spectral-sensitivity curves of photoreceptors can both contribute to color constancy. In the last part of the paper I derive the relation between the number of photoreceptor classes present in vision and the "filtering" properties of each class. The results of this analysis reverse a conclusion reached by Barlow: the "filtering" properties of human photoreceptors are consistent with a trichromatic visual system that is color constant.

Analysis of Variance↗
PubMed1990

The color-opponent and broad-band channels of the primate visual system.

Physiological, anatomical and psychophysical studies have identified several parallel channels of information processing in the primate visual system. Two of these, the color-opponent and the broad-band channels, originate in the retina and remain in part segregated through several higher cortical stations. To improve understanding of their function, recent studies have examined the visual capacities of monkeys following selective disruption of these channels. Color vision, fine- but not coarse-form vision and stereopsis are severely impaired in the absence of the color-opponent channel, whereas motion and flicker perception are impaired at high but not low temporal frequencies in the absence of the broad-band channel. The results suggest that the color-opponent channel extends the range of vision in the spatial and wavelength domains, and that the broad-band channel extends it in the temporal domain. Lesion studies also indicate that these channels must reach higher cortical centers through extrastriate regions other than just area V4 and the middle temporal area, and that the analysis performed by these two regions cannot be uniquely identified with specific visual capacities.

Animals↗
PubMed1992

The Ishihara Test: on the prevention of job discrimination.

Experiments were carried out to answer questions relative to the use of the 24-plate edition of the Ishihara Test for Colour-Blindness as a screening instrument for detecting the presence of inherited color defective vision. Subjects and their numbers varied between some experiments. Some subjects had normal color vision and others had inherited color defectiveness as confirmed with a Nagel anomaloscope. Most of the 157 subjects who participated in the experiments were either young deaf college students or police recruits with normal hearing who did not pass the Ishihara Test during their respective visual screening processes. Some hearing faculty and staff participated as part of Experiment 2. Item analysis and statistics applied to test the significance of differences between group means were applied to derive the following results: (a) test-retest reliability for the Ishihara is high both for persons with inherited color defectiveness and normal color vision; (b) persons making fewer than five errors on the first 13 plates made common incidental (nontypical) errors not related to color defective vision; and (c) five (5) or more errors was identified with some degree of inherited color defective vision, and subsequent referral for additional color vision diagnostics is warranted. Failure to utilize the recommended "pass-fail" criterion and/or to allow clients who fail color vision screening recourse to additional testing to establish type and degree of color defective vision may unnecessarily lead to job discrimination and/or interfere in a negative manner with the career selection process.

Adolescent↗
PubMed1974

Evidence of complementary afterimages in the pigeon.

Key pecking of pigeons was reinforced on a variable-interval schedule when ambient illumination came from a green light, but not when it came from a red, yellow, or white light. The different hues were randomly presented for periods of 30 sec each, with the restriction that white never followed red. After discriminative control was established, the pigeons were tested with the same procedure used during training, except that white sometimes followed red. Significantly more responses were made during white-following-red than during white following either green or yellow. These findings indicate that, in changing from red to white, complementary afterimages can be induced in pigeons for a brief period of time. By providing behavioral evidence for afterimages in the pigeon, this technique may be useful to research in comparative neurophysiology, animal discrimination learning, and theories of color vision.

Afterimage↗
PubMed2006

Ommatidial type-specific interphotoreceptor connections in the lamina of the swallowtail butterfly, Papilio xuthus.

The eye of the butterfly Papilio xuthus contains a random array of three types of ommatidia (types I-III), each bearing nine photoreceptors, R1-R9. Of the six spectral classes of photoreceptors identified, types I, II, and III ommatidia contain four, three, and two classes, respectively: the ommatidia are thus spectrally heterogeneous. The photoreceptors send their axons to the lamina where, together with some large monopolar cells (LMCs), the nine from a single ommatidium contribute to a module called a lamina cartridge. We recently reported that among different photoreceptor axon terminals visualized by confocal microscopy, the number and length of axon collaterals differ for different spectral receptors, suggesting that lamina circuits are specific for each ommatidial type. Here we studied the distribution of synapse-like structures in the cartridges, first characterizing a photoreceptor by measuring its spectral sensitivity and then injecting Lucifer yellow (LY). We subsequently histologically identified the type of ommatidium to which the injected photoreceptor belonged, cut serial ultrathin sections of the entire lamina, labeled these with anti-LY immunocytochemistry, and then localized synapse-like structures. We found numerous interphotoreceptor contacts both within and between cartridges, the combination of which was again specific for the ommatidial type. R3 and R4, which are green-sensitive photoreceptors in all ommatidia, have thick axons lacking collaterals. We found that these cells exclusively make contacts with LMCs and not with photoreceptors. We therefore presume that R3 and R4 construct a system for motion vision, whereas other randomly distributed spectral types provide inputs for color vision.

Animals↗
PubMed1994

Pseudophakic erythropsia.

BACKGROUND: Erythropsia is a temporary distortion of color vision where objects take on an abnormal reddish hue. Several drugs and disease conditions are associated with this acquired color anomaly. The following case reports identify one of these predisposing factors-pseudophakia. METHODS: Two pseudophakic adult white males were examined on separate occasions following complaints of transient reddening of vision after being outdoors. One patient was a monocular pseudophake with a posterior chamber intraocular lens, while the other had bilateral anterior chamber implants. None of the intraocular lens implants involved were ultraviolet-absorbing. RESULTS: Both patients were diagnosed with pseudophakic erythropsia. They were reassured and monitored routinely. At subsequent follow-up visits no recurrence of the symptoms was reported. CONCLUSIONS: The mechanism of pseudophakic erythropsia remains obscure, but its association with exposure to high levels of ultraviolet light is well documented. While generally benign, its appearance may be disconcerting to the patient, and the use of additional ultraviolet protection can be recommended.

Aged↗
PubMed1981

Scaling of color sensation by magnitude estimation: a contribution to opponent-colors theory.

Saturation and hue perceived in monochromatic stimuli and in light mixtures were scaled psychophysically by a direct magnitude estimation method. The colors were of aperture mode and were presented against a dark background. As a result opponent-colors functions were obtained which show the hue sensations produced by the lights of the visible spectrum (under the observing conditions used). Compared to the opponent-colors functions of Hurwich and Jameson, obtained by a cancellation technique, the subjective hue sensation differed significantly. It may be concluded that these cancellation functions describe an earlier, probably a retinal level of data processing, while our results may be regarded as a description of the output of the color vision system.

Color Perception↗
PubMed2004

Recessive NRL mutations in patients with clumped pigmentary retinal degeneration and relative preservation of blue cone function.

Mice lacking the transcription factor Nrl have no rod photoreceptors and an increased number of short-wavelength-sensitive cones. Missense mutations in NRL are associated with autosomal dominant retinitis pigmentosa; however, the phenotype associated with the loss of NRL function in humans has not been reported. We identified two siblings who carried two allelic mutations: a predicted null allele (L75fs) and a missense mutation (L160P) altering a highly conserved residue in the domain involved in DNA-binding-site recognition. In vitro luciferase reporter assays demonstrated that the NRL-L160P mutant had severely reduced transcriptional activity compared with the WT NRL protein, consistent with a severe loss of function. The affected patients had night blindness since early childhood, consistent with a severe reduction in rod function. Color vision was normal, suggesting the presence of all cone color types; nevertheless, a comparison of central visual fields evaluated with white-on-white and blue-on-yellow light stimuli was consistent with a relatively enhanced function of short-wavelength-sensitive cones in the macula. The fundi had signs of retinal degeneration (such as vascular attenuation) and clusters of large, clumped, pigment deposits in the peripheral fundus at the level of the retinal pigment epithelium (clumped pigmentary retinal degeneration). Our report presents an unusual clinical phenotype in humans with loss-of-function mutations in NRL.

Amino Acid Motifs↗
PubMed2006

Spectral statistics in natural scenes predict hue, saturation, and brightness.

The perceptual color qualities of hue, saturation, and brightness do not correspond in any simple way to the physical characteristics of retinal stimuli, a fact that poses a major obstacle for any explanation of color vision. Here we test the hypothesis that these basic color attributes are determined by the statistical covariations in the spectral stimuli that humans have always experienced in typical visual environments. Using a database of 1,600 natural images, we analyzed the joint probability distributions of the physical variables most relevant to each of these perceptual qualities. The cumulative density functions derived from these distributions predict the major colorimetric functions that have been reported in psychophysical experiments over the last century.

Color Perception↗
PubMed1975

Ultraviolet and green receptors in principal eyes of jumping spiders.

Spectral sensitivities of cells in principal eyes of the jumping spider Phidippus reqius were measured using techniques of intracellular recording. Three types of cells were found. UV cells had peak sensitivities at 370 nm and were over 4 log units less sensitive at wavelengths longer than 460 nm. Green-sensitive cells had spectral sensitivities which were well fit by nomogram curves peaking at 532 nm. UV-green cells had dual peaks of sensitivity at about 370 and 525 nm, but the ratios of UV-to-green sensitivities varied over a 40: 1 range from cell to cell. Moreover, responses of UV-green cells to flashes of UV light were slower than to flashes of green light. Segregation of receptor types into the known layers of receptors in these eyes could not be shown. It is concluded that jumping spiders have the potential for dichromatic color vision.

Animals↗
PubMed1983

Chromatic adaptation and the blue-green side of the color triangle.

This is an attempt to show with chromatic adaptation data that the line tangent to the spectrum locus at about 460 nm and passing through the tritanopic confusion point represents the blue-green leg of the triangle of fundamental colors. The inability to use chromatic adaptation to produce colors in the green corner of the triangle has been explained in terms of a zone theory of color vision.

Adaptation, Ocular↗
PubMed1995

Colors of maximal saturation.

The spectrum locus on the CIE Chromaticity Diagram represents monochromatic stimuli which have been exposed to a dark adapted fovea. Some of these colors can be made to appear more saturated by chromatic adaptation. The colors both inside the spectrum locus and the supersaturated colors outside are bounded by a four-sided boundary line which constitutes the locus of colors of maximal saturation. An attempt has been made to show how this quadrilateral is related to the fundamental colors and to a zone theory of color vision.

Adaptation, Physiological↗
PubMed1996

Polarization contrast vision in Octopus.

While the ability to analyze polarized light is widespread among animals, its contribution to form vision has not yet been documented. We tested the hypothesis that polarization vision can be used for object discrimination, by training octopuses to distinguish between targets on the basis of the presence or absence of a pattern produced by a 90 degrees polarization contrast within the target. Octopuses recognized a 90 degrees contrast pattern within a single target, when presented either on a horizontal/vertical axis or on a 45 degrees/135 degrees axis. They were able to transfer their learning to new situations and to detect a polarization contrast when the orientations of the e-vector of light passing through the target center and background differed by as little as 20 degrees. Polarization vision may provide information similar to that available from color vision and thus serve to enhance the detection and recognition of objects.

Animals↗
PubMed1961

Industrial visual screening. Advantages and disadvantages of various instruments.

The ideal test for visual screening is one which is easily performed by a technician with limited training, inexpensive and not time-consuming, easily understandable by all applicants, and one which will correspond generally with a more thorough examination by an ophthalmologist. The ideal screening technique should test accurately those functions needed for any particular occupation. The visual screeners now in great preponderance have certain advantages for ease and are generally acceptable for approximating the visual acuity. Visual screeners do not accurately test the astigmatic applicant, and they have not proven their value in testing depth perception and color vision. The use of the Harrington Flocks Screener is recommended for testing the visual field. The use of the Verhoeff Steropter for depth perception and the American Optical pseudoisochromatic plates for color testing is recommended when these tests are needed. The old Snellen test cards, or the projector chart for measuring distance vision, and the test cards for measuring near vision are often much more reliable than are the visual screeners.

Color Vision↗