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PubMed1992

Depth capture and transparency of regions bounded by illusory and chromatic contours.

Spillmann and Redies noted that when a transparent textured pattern is held above the Ehrenstein figure, the subjective surfaces appear to lie not in the plane of the figures but in the plane of the overlying texture. In Experiment 1, we tested this phenomenon with chromatic squares and found that the perceived depth of regions bounded by the chromatic contours was captured by overlying texture planes when the square was equiluminous with the background. We then tested this phenomenon with a variety of illusory contour stimuli and found that it only occurs with figures involving fine line terminators, and not, for example, with the solid Kanizsa triangle. These results suggest that chromatic contours and the illusory contours induced by line terminators provide only weak binocular disparity signals and that these signals are easily overwhelmed by the disparity signals from the overlying luminance texture.

Color Perception↗
PubMed1993

Chromatic aberration and accommodation: their role in emmetropization in the chick.

The roles of chromatic aberration and accommodation as cues to emmetropization in the chick were investigated. Myopia was induced monocularly by lid suture for a period of 1-2 weeks from hatching, after which eyes were reopened and the recovery process followed. Monochromatic light (ML) rearing conditions and ciliary nerve section surgery were used to eliminate chromatic aberration and accommodative activity respectively. Control animals were reared in white light (WL). When accommodation was left intact, chickens reared under monochromatic light were able to recover normally. However, ciliary nerve section produced hyperopia, deepening of the anterior chamber and a tendency towards axial lens thinning, irrespective of the light conditions used. Hyperopic refractive errors peaked at 4 weeks (mean refractive errors: +5.7 D, +4.21 D for ML, WL groups respectively, 4 weeks), with the ML group still exhibiting significant hyperopia at 7 weeks. Ciliary nerve section did not prevent the myopic response to lid suture (mean refractive errors: -22.65 D; -25 D for ML, WL groups respectively, 1 week) nor the elimination of myopia when eyes were reopened. These data indicate that neither accommodation nor chromatic aberration are fundamental to the gross operation of the emmetropization process although they may be essential for the fine tuning of refraction.

Accommodation, Ocular↗
PubMed1993

Simultaneous luminance contrast with chromatic colors.

The variations in the color of a test field of constant luminance during changes in the luminance of a contiguous inducing field was measured psychophysically. The fields had the same hue (red, green, or blue). The colors induced in the test field could be specified by the strength of a chromatic quality, and by the strength of the opponent qualities luminous/black. The psychophysical relationship between the two kinds of perceptive variables and test and inducing luminance followed distinctly different functions. The luminous/black variable varied linearly with contrast over a large range, as previously found for achromatic colors. The contrast gain of the luminous/black variable for the red and green colors was the same as for achromatic colors. The gain for the blue colors was twice the gain for the other colors. The chromatic variables were primarily related to the local luminance. For a given test luminance they were maximal near zero contrast. They followed the same function as the white component of achromatic colors. It is suggested that the luminous/black variable is related to spectrally broadband cells with a strong center/surround antagonism, while the chromatic variables and white are related to cells that lack a spectrally broadband surround in their receptive field.

Color Perception↗
PubMed1993

Motion perception with spatiotemporally matched chromatic and achromatic information reveals a "slow" and a "fast" motion system.

Recent reports dealing with apparent motion challenged the standard view according to which motion processing should be impossible if the visual attributes matched across space and time are processed in independent channels (the similarity principle). The present work examines this possibility insofar as it relates to the spatiotemporal combination of pure chromatic and pure luminance information. The data indicate that the "similarity principle" is indeed infringed at low (< or = 2.5 Hz, i.e. velocities of 2.5 deg/sec for spatial modulations of 1 c/deg, in this study) but not at high (> or = 7.5 Hz) temporal frequencies. The fact that colour and luminance may or may not combine to yield motion perception depending on their temporal modulation reconciliates contradictory results in the literature and supports the idea of two motion systems, a "fast"/specific one, integrating information only from similar subunits, and a "slow"/unspecific one, integrating information across dissimilar subunits (in the present case, across the chromatic and achromatic "domains"). This dichotomy is also supported by the finding that chromatic reverse-phi (i.e. with equiluminant, red and green stimuli) can be observed at medium temporal frequencies but is replaced by direct motion at low temporal frequencies, presumably within the range of the "slow"/unspecific system. Using a modified "minimum motion" technique (referred to as the Reverse-Phi equiluminance method) we present data allowing to assess the relative weights of the two systems as a function of temporal frequency.

Color Perception↗
PubMed1995

Color appearance with sparse chromatic context.

We compared changes in the appearance of a test region caused by introducing an inhomogeneous chromatic background to changes caused by a space-averaged equivalent uniform background. Subjects adjusted a test field presented on a CRT so that it appeared neither reddish nor greenish. Sparse "white" or "green" dots, randomly scattered throughout a "red" background field, caused a large decrease (up to 15 nm) in the dominant wavelength of the red/green equilibrium setting, compared to measurements with a uniform "red" background. A uniform background with the same space-averaged chromaticity and luminance as the complex background had an effect similar to the uniform "red" background. These results contradict theories of color constancy that rely on the "gray world" assumption, and indicate the significance for color perception of individual chromaticities within discrete, noncontiguous regions.

Adaptation, Ocular↗
PubMed1994

Velocity discrimination in chromatic gratings and beats.

It is commonly assumed that the ability to discriminate velocity in a stimulus directly reflects the properties of the underlying directionally-selective mechanism. The results presented here show that this assumption is not always correct. Speed discrimination tasks over a range of base velocities were carried out for luminance gratings, chromatic gratings and contrast (beat) gratings of equivalent periodicity and contrasts. At low contrasts (0.5 log units above detection threshold), speed discrimination in luminance gratings was at least twice as good (when expressed as a Weber fraction), than in either chromatic gratings or beats. This is similar to the situation seen for tasks of direction discrimination using these stimuli [e.g. Cropper and Derrington (1990) Perception, 19, A31]. When the stimulus contrasts were increased to 1.5 log units above detection threshold, the ability to discriminate speed in both chromatic and beat stimuli improved to a performance level comparable to that shown for luminance gratings at all contrasts. This effect is not seen for tasks of direction discrimination when the same increase in stimulus contrast has little effect on the lower threshold of motion (LTM) measured for beat patterns. These results indicate that the ability to discriminate velocity in a stimulus does not necessarily directly reflect the characteristics of the ability to discriminate the direction of motion of that stimulus.

Color Perception↗
PubMed1995

Infant luminance and chromatic contrast sensitivity: optokinetic nystagmus data on 3-month-olds.

Infant color vision is poor, and most psychophysical experiments agree that infant color vision emerges between ages 3 weeks and 3 months. Presumably, the color vision of infants is poor during the months immediately after it has emerged. We have tested two alternative explanations for the poor color vision of infants: (1) there is a special critical immaturity within the color pathways of infants; (2) infants have poor infant color vision because they are insensitive to contrast. Luminance and chromatic contrast thresholds were measured on 3-month-olds using optokinetic nystagmus (OKN), and adult luminance and chromatic contrast thresholds were measured using OKN and two forced-choice methods: direction-of-motion discrimination and grating detection. The infant chromatic-to-luminance contrast threshold ratio shows that infants are as sensitive or even more sensitive than adults to color, depending on the testing method used on adults. This result suggests that the general contrast insensitivity hypothesis is correct. Conservative "worst-case" quantitative analysis strongly suggests that this result is not the consequence of a luminance artifact.

Adult↗
PubMed2004

Effect of amphiphilic molecules upon chromatic transitions of polydiacetylene vesicles in aqueous solutions.

Effect of amphiphilic molecules upon the chromatic transitions of polymerized 10,12-pentacosadiynoic acid (PCDA) vesicles in aqueous solutions was reported. The colorimetric response of polymerized PCDA vesicles for 1-pentanol is higher than that for ethanol due to more hydrophobic property of 1-pentanol. The colorimetric response of polymerized PCDA vesicles for sodium dodecyl sulfate (SDS) and Triton X-100 is lower than that for cetyltrimethylammonium bromide (CTAB). The strong ability of CTAB to induce chromatic transition of the vesicles is related to the positively charged headgroups of CTAB, which favors approach of CTAB to the negatively charged carboxylate groups at the vesicle surface. The insertion of alkyl chain of CTAB into the hydrophobic domain perturbs the conformation of the conjugated polymer backbone and induces color change of polydiacetylene vesicles. For a series of alkylamine hydrochloric salts, the longer the alkyl chain, the stronger the ability of alkylamine to induce chromatic transition of polydiacetylene vesicles.

Acetylene↗
PubMed2004

Chromatic immunoassay based on polydiacetylene vesicles.

A new approach of chromatic immunoassay based on polydiacetylene vesicles is described. Antibodies were covalently coupled with mixed vesicles of 10,12-tricosadiynoic acid (TCDA) and dimyristoylphosphatidycholine (DMPC). The vesicle-antibody conjugates were irradiated with UV light to yield a blue-colored polydiacetylene. After antigen injection, specific immunoreactions took place at the vesicle surface alter polydiacetylene conformation and lead to a color change from blue to red. The chromatic immunoassay described here is simple, rapid, sensitive; the color change was readily discernible by naked eye when the concentration of antigen is 1 ng/mL. Incorporation of DMPC in the mixed vesicles increases the sensitivity of the chromatic immunoassay.

Acetylene↗
PubMed2005

Blue-light filtering intraocular lens in patients with diabetes: contrast sensitivity and chromatic discrimination.

PURPOSE: To evaluate potential changes in contrast sensitivity and color discrimination in diabetic patients who had cataract surgery and implantation of the blue-light filtering AcrySof Natural (SN60AT) intraocular lens (IOL) compared with an ultraviolet-only filtering (AcrySof SA60AT) IOL. SETTING: Refractive Surgery Unit, Hospital NISA Valencia al Mar, Valencia, Spain. METHODS: Forty-four eyes of 22 diabetic patients were enrolled in a blue-light filtering fellow-eye control study. Patients received yellow-tinted IOLs (AcrySof Natural) in 1 eye and non-yellow-tinted IOLs (AcrySof SA60AT) in the fellow eye. Three months after surgery, monocular contrast sensitivity function was measured with the CSV 1000-E contrast sensitivity chart at distance and color discrimination was tested with the Farnsworth-Munsell 100-hue test. RESULTS: Eyes implanted with the blue-light filtering IOLs showed better contrast sensitivity values than fellow eyes implanted with non-yellow-tinted IOLs (P<.05). The blue-light filtering IOL did not modify chromatic discrimination compared with the non-yellow-tinted IOL (P = .62). In the blue-yellow axis discrimination study, the eyes implanted with the AcrySof Natural IOL had statistically significant better color vision (P = .008). CONCLUSIONS: In diabetic patients, the AcrySof Natural IOL provides better contrast sensitivity than the AcrySof SA60AT. The blue-light filter of the AcrySof Natural IOL did not cause chromatic discrimination defects based on total error scores and improved color vision in the blue-yellow chromatic axis in diabetic patients.

Aged↗
PubMed2004

Patterns of chromatic information processing in the lobula of the honeybee, Apis mellifera L.

The honeybee, Apis mellifera L., is one of the living creatures that has its colour vision proven through behavioural tests. Previous studies of honeybee colour vision has emphasized the relationship between the spectral sensitivities of photoreceptors and colour discrimination behaviour. The current understanding of the neural mechanisms of bee colour vision is, however, rather limited. The present study surveyed the patterns of chromatic information processing of visual neurons in the lobula of the honeybee, using intracellular recording stimulated by three light-emitting diodes, whose emission spectra approximately match the spectral sensitivity peaks of the honeybee. The recorded visual neurons can be divided into two groups: non-colour opponent cells and colour opponent cells. The non-colour opponent cells comprise six types of broad-band neurons and four response types of narrow-band neurons. The former might detect brightness of the environment or function as chromatic input channels, and the latter might supply specific chromatic input. Amongst the colour opponent cells, the principal neural mechanism of colour vision, eight response types were recorded. The receptive fields of these neurons were not centre surround as observed in primates. Some recorded neurons with tonic post-stimulus responses were observed, however, suggesting temporal defined spectral opponency may be part of the colour-coding mechanisms.

Animals↗
PubMed2004

The application of chromatic dark-adapted kinetic perimetry to retinal diseases.

PURPOSE: To demonstrate the value of a 2-color perimetric procedure for determining cone and rod system contributions to the dark-adapted kinetic visual field (VF). DESIGN: Prospective evaluation of perimetric testing procedure. PARTICIPANTS: Five patients with retinal diseases and 6 visually normal individuals. METHODS: Long- and short-wavelength stimuli were presented under dark-adapted conditions in a Goldmann perimeter. Visual fields were measured for the II and V test target sizes with a long-wavelength filter (cut-on at 600 nm) and a short-wavelength filter (cutoff at 510 nm). Light intensities through these filters were matched scotopically for the rod system by producing equal peripheral boundaries on 6 visually normal individuals. To validate the application of this procedure, we tested a patient with congenital achromatopsia and another patient with congenital stationary night blindness (CSNB). We then tested 2 patients with retinitis pigmentosa (RP) and 1 patient with Usher's syndrome to determine the cone and rod contributions to their VF isopters. MAIN OUTCOME MEASURES: Isopters for long- and short-wavelength test stimuli, and the appearance of the test stimuli, whether reported as chromatic or achromatic. RESULTS: The patient with congenital achromatopsia showed superimposed isopters for the 2 stimuli, which were reported as achromatic, demonstrating that the peripheral field boundaries were rod mediated. The patient with CSNB showed an isopter in response to the long-wavelength stimulus that was considerably larger than that in response to the short-wavelength stimulus, both stimuli reported as chromatic, showing that the cone system determined peripheral thresholds for both stimuli. In 2 patients with RP, we observed a mixed pattern of cone or rod system detection of the chromatic stimuli. The peripheral isopters were rod mediated, whereas the cone system determined the central field isopters. In an Usher's syndrome patient, cones mediated both the peripheral and the central field isopters. CONCLUSIONS: A 2-color dark-adapted Goldmann perimetric procedure was able to determine whether the VF isopters were rod or cone mediated in 5 patients with various forms of retinal disease.

Adult↗
PubMed2005

Modulation of sensory photophobia in essential blepharospasm with chromatic lenses.

PURPOSE: To determine the effect of photochromatic modulation with tinted lenses on the sensory symptoms of photophobia in blepharospasm patients. DESIGN: Nonrandomized case-control study. PARTICIPANTS: Thirty-four subjects (24 benign essential blepharospasm patients and 10 normal controls). METHODS: Subjects were seated in front of a calibrated light source. Beginning at 0%, the intensity of the light source was increased gradually until the patient reported symptomatic photophobia. The intensity of the light source was then measured with a light meter. This procedure was performed first with no chromatic lens and then with 7 different chromatic lenses, each blocking specific wavelengths of the visible spectrum. The subject was then asked which lens provided the greatest symptomatic improvement of photophobia. Statistical significance was calculated with analysis of variance and t test analysis. MAIN OUTCOME MEASURES: Objective measurement of light intensity tolerated and subjective assessment of photophobia were obtained for each chromatic lens tested. RESULTS: The light intensity tolerated by the normal subjects compared with the blepharospasm group was not statistically significant with no lens, but grew to 3.5 times that tolerated by the blepharospasm group as more of the higher wavelengths of the visible spectrum were blocked (P = 0.048). Lenses 4, 5, 6, and 7 allowed blepharospasm patients to tolerate a significantly higher intensity of light when compared with no lens (P = 0.04, P = 0.007, P = 0.03, and P = 0.01, respectively). Although the highest intensity of light tolerated was measured with lens 6, 71% of blepharospasm patients reported the greatest relief of photophobia with lens 7. CONCLUSIONS: Blepharospasm patients tolerate a lower intensity of light when compared with normal subjects; this differential in light tolerance becomes significantly more pronounced as the higher wavelengths of the visible spectrum are blocked. The symptoms of photophobia in blepharospasm patients can be reduced significantly with photochromatic modulation. Despite lens 6 allowing the patients to tolerate a higher intensity of light, the majority of patients preferred lens 7 for symptomatic relief of photophobia. These findings suggest that sensory photophobia may be related more to the wavelength than to the intensity of the light exposure.

Blepharospasm↗
PubMed2005

Breaking the spherical and chromatic aberration barrier in transmission electron microscopy.

Since the invention of transmission electron microscopy (TEM) in 1932 (Z. Physik 78 (1932) 318) engineering improvements have advanced system resolutions to levels that are now limited only by the two fundamental aberrations of electron lenses; spherical and chromatic aberration (Z. Phys. 101 (1936) 593). Since both aberrations scale with the dimensions of the lens, research resolution requirements are pushing the designs to lenses with only a few mm space in the pole-piece gap for the specimen. This is in conflict with the demand for more and more space at the specimen, necessary in order to enable novel techniques in TEM, such as He-cooled cryo electron microscopy, 3D-reconstruction through tomography (Science 302 (2003) 1396) TEM in gaseous environments, or in situ experiments (Nature 427 (2004) 426). All these techniques will only be able to achieve Angstrom resolution when the aberration barriers have been overcome. The spherical aberration barrier has recently been broken by introducing spherical aberration correctors (Nature 392 (1998) 392, 418 (2002) 617), but the correction of the remaining chromatic aberrations have proved to be too difficult for the present state of technology (Optik 57 (1980) 73). Here we present an alternative and successful method to eliminate the chromatic blur, which consists of monochromating the TEM beam (Inst. Phys. Conf. Ser. 161 (1999) 191). We show directly interpretable resolutions well below 1A for the first time, which is significantly better than any TEM operating at 200 KV has reached before.

Lenses↗
PubMed2005

A method of dynamic chromatic aberration correction in low-voltage scanning electron microscopes.

A time-of-flight concept that dynamically corrects for chromatic aberration effects in scanning electron microscopes (SEMs) is presented. The method is predicted to reduce the microscope's chromatic aberration by an order of magnitude. The scheme should significantly improve the spatial resolution of low-voltage scanning electron microscopes (LVSEMs). The dynamic means of correcting for chromatic aberration also allows for the possibility of obtaining high image resolution from electron guns that have relatively large energy spreads.

Journal Article↗
PubMed2004

Accommodation with and without short-wavelength-sensitive cones and chromatic aberration.

Accommodation was monitored while observers (23) viewed a square-wave grating (2.2 cycles/deg; 0.53 contrast) in a Badal optometer. The grating moved sinusoidally (0.2 Hz) to provide a stimulus between -1.00 D and -3.00 D during trials lasting 40.96 s. There were three illumination conditions: 1. Monochromatic 550 nm light to stimulate long-wavelength-sensitive cones (L-cones) and medium-wavelength-sensitive cones (M-cones) without chromatic aberration; 2. Monochromatic 550 nm light+420 nm light to stimulate long-, medium- and short-wavelength-sensitive cones (S-cones) with longitudinal chromatic aberration (LCA); 3. Monochromatic 550 nm light+420 nm light to stimulate L-, M- and S-cones viewed through an achromatizing lens. In the presence of LCA mean dynamic gain decreased (p=0.0003; ANOVA) and mean accommodation level was reduced (p=0.001; ANOVA). The reduction in gain and increased lag of accommodation in the presence of LCA could result from a blue-yellow chromatic signal or from a larger depth-of-focus.

Accommodation, Ocular↗
PubMed2005

Estimating chromatic contrast thresholds from the transient visual evoked potential.

Chromatic contrast thresholds may be estimated from transient VEPs by measuring the peak-to-peak amplitude at a range of stimulus levels followed by extrapolation to zero amplitude. However, there have been reports of failure of this technique when applied to the transient chromatic VEP due to variability of amplitude, difficulties with component identification and poor correlation of amplitude with stimulus level. The aim of our study was to compare methods of transient VEP chromatic contrast threshold estimation in terms of success rate and comparison with psychophysical threshold. We found each of the methods we investigated to have a high success rate, and in most cases VEP and psychophysical thresholds did not differ significantly.

Adult↗
PubMed2005

Chromatic assimilation measured by temporal nulling.

Chromatic assimilation is the shift in color appearance toward nearby light. Assimilation was measured using nearby light with time-varying chromaticity. This light induced time-varying assimilation within the test area. Assimilation was quantified by the amplitude of temporally varying test-area light--in counter-phase to the induced assimilation--required to null the assimilation. Unlike previous studies of assimilation, observers here judged only the steadiness of the test area, not its color. The inducing light was varied in luminance, temporal frequency and chromaticity. The measured assimilation could not be explained by only optical factors affecting receptoral quantal absorption. This implies a neural process contributes to assimilation. The nulling measurements showed also that assimilation was not induced independently within the L/M- and S-cone pathways.

Adult↗