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Three centuries of experimentation in optics, psychophysics and biochemistry established the dependence of color vision on three kinds of light-absorbing molecules, or pigments, in the cone cells of the retina. The author has isolated the genes that encode the pigments and has identified genetic anomalies that lead to color blindness.
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PURPOSE: To evaluate and compare the functional and perceived benefits of wearing coloured lenses by patients with age-related macular degeneration (ARMD). METHOD: Ten subjects with early ARMD and five elderly controls wore a selection of NoIR wrap-around coloured lenses (yellow 29.7% light transmission, orange 22.9%, red 16.8% and grey 10.3%), each for a duration of 7 days. Contrast sensitivity, colour vision, visual acuity, the effect of glare and peripheral sensitivity were measured for each lens and compared with a control (no lens) condition. Subjective ratings of visual performance were also scored. RESULTS: Compared with the no filter condition, red and grey lenses reduced contrast sensitivity whereas yellow and orange lenses increased contrast sensitivity. These objective changes were supported by subjective ratings in subjects with ARMD. Grey lenses reduced the loss of contrast sensitivity usually suffered in the presence of glare, whereas visual acuity and peripheral sensitivity decreased with red lenses. Colour vision became distorted with red lenses in control subjects, but was relatively unaffected by the use of coloured lenses in subjects with ARMD. CONCLUSIONS: The subjective benefit of coloured lenses appears to be due to a minor enhancement of contrast sensitivity.
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UNLABELLED: Visual hallucinations (VH) are seen in about a third of all patients with Parkinson's disease (PD) and are usually considered to be an early marker or clinical component of a dopaminergic psychosis. Their peculiar phenomenology has not yet been studied in a systematic manner. METHODS: A semi-structured interview was performed twice in 62 PD patients. Different motoric and cognitive disease scales were used. The patients were not demented or depressed and had no other psychotic features other than hallucinations. Their visions was at least 0.6. RESULTS: 22 patients (36%) reported complex visual hallucinations or illusions in both interviews. These patients were not different from the non-hallucinating patients in terms of age, duration and stage of the disease, dosage and type of medication and frequency of cataracts. VH were diurnal in 41% of the patients, nocturnal in 18% of the patients and mixed in 41 patients. They were seen at least once weekly in 67% and they lasted always less than an hour. VH most frequently involved adults, children and pets. They were often mobile and had normal size and physiognomy. Notable emotional reactions were only reported by 18% of the patients. DISCUSSION: The phenomenology of VH in PD differs from VH in exogenous or endogenous psychoses, but is similar to the Charles Bonnet-syndrome (CBS), appearing in elderly patients with different visual deficits. As PD patients suffer regularly from visual deficits of contrast and color perception, a similar pathogenesis to CBS can be hypothesized, with these "minor" and benign VH being due to "release phenomena" in relation to partial visual deprivation. The lack of multimodality hallucinations and of secondary paranoia as well as the clear sensorium are helpful features in distinguishing them from toxic psychosis.
Synaesthesia and eidetic imagery are both syncretic experiences entailing a dedifferentiation of perceptual qualities. In this paper the correlation between synaesthesia and eidetic imagery is explored. Ten subjects selected for possible eidetic and/or synaesthetic ability were tested in a battery of tasks that tap structural and typographic eidetic imagery, and colour-hearing and colour-mood synaesthesia. It was found that both structural and typographic eidetic imagery were correlated with measures of synaesthesia, indicating a relationship between the two phenomena.
Interviews with a multilingual synesthete (MLS), who experiences colored letters for Roman and Cyrillic alphabets and for digits, revealed stable synesthetic experiences over 2 1/2 - 5 years. Colors of Cyrillic letters were based on Roman letters. Four Stroop tests involving both types of letters showed that MLS was able to name print color faster if the colors matched her synesthetic colors, showing that synesthesia is automatic. Letter-naming times for blocks of color were slower than those of actual letters, supporting unidirectionality of synesthesia. Stroop tests with Roman, but not Cyrillic, letters showed MLS acquired new temporary letter-color pairings and her color-naming times for these were not different from those for her original synesthetic colors.
There is enormous variation in the X-linked L/M (long/middle wavelength sensitive) gene array underlying "normal" color vision in humans. This variability has been shown to underlie individual variation in color matching behavior. Recently, red-green color blindness has also been shown to be associated with distinctly different genotypes. This has opened the possibility that there may be important phenotypic differences within classically defined groups of color blind individuals. Here, adaptive optics retinal imaging has revealed a mechanism for producing dichromatic color vision in which the expression of a mutant cone photopigment gene leads to the loss of the entire corresponding class of cone photoreceptor cells. Previously, the theory that common forms of inherited color blindness could be caused by the loss of photoreceptor cells had been discounted. We confirm that remarkably, this loss of one-third of the cones does not impair any aspect of vision other than color.
In East African Lake Victoria >200 endemic species of haplochromine fishes have been described on the basis of morphological and behavioral differences. Yet molecular analysis has failed to reveal any species-specific differences among these fishes in either mitochondrial or nuclear genes. Although the genes could be shown to vary, the variations represent trans-species polymorphisms not yet assorted along species lines. Nevertheless, fixed genetic differences must exist between the species at loci responsible for the adaptive characters distinguishing the various forms from one another. Here we describe variation and fixation at the long wavelength-sensitive (LWS) opsin locus, which is selection-driven, adaptive, and if not species- then at least population-specific. Because color is one of the characters distinguishing species of haplochromine fishes and color perception plays an important part in food acquisition and mate choice, we suggest that the observed variation and fixation at the LWS opsin locus may have been involved in the process that has led to the spectacular species divergence of haplochromine fishes in Lake Victoria.
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Fifty HIV-infected individuals and 20 uninfected controls participated in an investigation of dual task performance in HIV-1 infection. Participants first engaged in a simple auditory reaction time (RT) task followed by a visual choice RT task (single task condition), and then they simultaneously engaged in both tasks (dual task condition). Under single task conditions, the HIV+ participants did not significantly differ from controls on either simple or choice RT (though a trend was evident on single task choice RT). In contrast, under dual task conditions the HIV+ group's performance decrement, relative to controls, was significantly greater on both simple and choice RT. This dual task decrement was also significantly associated with slower performance on the interference condition of the Stroop. Patients with AIDS tended to have greater dual task decrements than did the pre-AIDS group, though this fell short of statistical significance. These results suggest that HIV-1 infection leads to deficits in divided attention and the simultaneous processing of competing stimuli, deficits which have been linked to disruption of the anterior attentional system.
PURPOSE: Congenital color-vision deficiencies are frequent among males, 4.7-8.0%, suggesting that female carriers are present at a frequency of 9-15%. The purpose of this study was to determine whether carriers could be detected by analysis of the visual pigment genes. METHODS: DNA from 29 males with congenital color-vision deficiencies, from their mothers, and from 117 randomly-selected females was analyzed. The most upstream genes, the downstream genes, and the most downstream genes in the red/green pigment gene arrays were amplified separately by PCR. Exon 5 of each gene was analyzed by single-strand conformation polymorphisms (SSCP). RESULTS: Analysis of the visual pigment genes suggests that one of the 29 mothers examined is a female protan and two others are carriers of both protan and deutan defects. The remaining 26 mothers were confirmed to be carriers of congenital color-vision deficiencies. Unusual patterns were observed in 15 (13%) of the randomly-selected females; among them, 5 appeared to be protan carriers and at least 4 to be deutan carriers. CONCLUSIONS: Female carriers of congenital color-vision deficiencies can be detected by analysis of the visual pigment genes. Since the proportion of females showing unusual patterns was slightly higher than expected, some must be false-positives and require more detailed examination.
In a previous randomized placebo-controlled clinical trial, we observed significant visual field enlargements induced by computer-based restitution training in patients with cerebral lesions (Kasten et al., Nature med., 4, 1998, 1083-87). Now we asked the question whether this effect is stable after training was discontinued? Here we report data of a follow-up study after a training-free interval (mean 23.5 +/- 2.3 months after end of therapy). 16 patients of the original restitution group and 6 patients of the placebo group were re-examined. On average, in high resolution computer campimetry (stimulus detection: PeriMa, form recognition: PeriForm, color perception: PeriColor) as well as in conventional automatic perimetry (TAP-2000) both groups showed no significant decline in the number of correctly detected stimuli after training was discontinued. However, cluster analysis revealed three different types of patients, who showed either increase (Type-I), decrease (Type-II) or stability (Type-III) in performance. We propose that many patients learn to use the regained visual capacities not only in the setting of a computer training but also in every day life, while other patients do not use the areas of restored vision and show a decrease of visual functions after the end of training. The Type-I group does not need continuous training, while the Type-II group may benefit from phases of refreshment exercises.
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Many design guidelines encourage maintaining stimulus-response compatibility whenever possible. Payne found that naïve judgments for different stimulus-response (S-R) mappings were not very accurate, and suggested that designers may not be able to predict whether a particular display-control configuration will lead to better performance than another. Three experiments were conducted to determine whether naïve judgments for two-choice tasks in which stimuli and responses involve left-right spatial information are sensitive to (a) the influence of S-R mode relations and (b) pure versus mixed presentation of compatible and incompatible mappings. Initial performance judgments for these conditions were not very accurate, nor were those for four-choice tasks of the type studied by Payne, but subjects' estimates of performance improved with relatively little experience using the different S-R configurations.