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PubMed1995

Eigenvector interpretation of the Farnsworth-Munsell 100-hue test.

We measured the reflectance spectra for the 85 color caps of the Farnsworth-Munsell 100-hue test. Eigenvectors and eigenvalues of a correlation matrix of cone responses were computed, with the cone responses being determined from the 85 test caps, arranged in order (according to color) by means of a linear model. It is shown that the Farnsworth-Munsell 100-hue test can be simulated by use of eigenvectors of the cone responses. The eigenvectors can be interpreted as nonopponent signal and opponent color signals. The normal observer can determine the color of a cap by using two opponent color signals. For color-blind persons (dichromats) one or the other opponent signal is defective, and errors can occur during the test. The simulation results also suggest that eigenvectors can be used to predict results of arrangement tests similar to the Farnsworth-Munsell 100-hue test.

Color Perception↗
PubMedDate not supplied

[Chromatic sense: types of defects and clinical evaluation tests].

Evaluation of the chromatic sense has a great value in ophthalmic practice, both for diagnosis of the congenital defects (daltonism), as well as for diagnosis and follow-up of acquired defects. Many clinical tests are available to be used for this purpose. However it is necessary to know the details and sensitivity of each test, since there are many variations in the results, depending on the searched condition, if congenital or acquired pathologies. Our goal is to review the types of defects of the chromatic sense and provide information about the main current available tests and their best purpose. We further emphasize the importance of standard illumination procedure in the application of the tests.

Color Perception↗
PubMed1986

City tests and information theory.

The responses of 455 male subjects on both editions of the City University Colour Vision Tests (City 1 and City 2) were recorded after the establishment of each subject's criterial status using the Nagel anomaloscope. Based on the Information Theory, each plate was assigned a contributory weighted score to the total test score. Using informational analysis, a cut-off point in test score separating normals and defectives was also determined for each test. This scoring system is an improvement on the existing (or manufacturer's) system. The analysis has also shown that the second edition (City 2) is a considerable improvement on the first (City 1). Despite this, even the improved City 2, like its origin, the D-15, is shown to be poorer than most of the commonly used PIC tests.

Adolescent↗
PubMed2004

Chromatic edges, surfaces and constancies in cerebral achromatopsia.

We tested achromatopsic observer, MS, on a number of tasks to establish the extent to which he can process chromatic contour. Stimuli, specified in terms of cone-contrast, were presented in a three-choice oddity paradigm. First we show that MS is able to discriminate the magnitude of chromatic and luminance contrast, but performance is inferior to that of normal observers. Moreover, MS can discriminate isoluminant borders of different chromatic composition. These abilities are not the result of unintended luminance differences and are abolished when chromatic borders are masked by sharp luminance change. In simple displays, local cone-contrast signals can make a significant contribution to surface colour appearance in normal observers. In more complex displays, the perception of a surface's colour becomes largely independent of the local contrast to its background, via processes presumed to be similar to the edge integration and anchoring stages of Land's Retinex algorithm. We show that in simple displays the percepts of both MS and normal observers are dominated by local chromatic-contrast. But, although the percepts of normal observers change in line with the predictions of retinex theory in more complex displays, those of MS do not, remaining dominated by local contrast signals. We conclude that MS has lost the ability to perform edge integration and that this loss is closely related to his absence of colour experience.

Adult↗
PubMed1985

Distance, duration and blur effects on the perception of pseudoisochromatic stimuli.

Two experiments are reported that examine the effects of viewing distance, viewing duration, and stimulus clarity on performance with three popular versions of the pseudoisochromatic tests of colour deficiency. With a large sample of colour-normal observers, highly significant effects of these viewing conditions are found. In addition, large differences in sensitivity to these conditions are obtained among the three tests employed (The American Optical Corporation test, the Dvorine test, and the Ishihara test). Results are discussed in terms of practical implications for test administration and in terms of likely processes, in addition to colour discrimination, assessed by these tests.

Adult↗
PubMed1996

Human colour discrimination based on a non-parvocellular pathway.

BACKGROUND: Traditionally, colour information is assumed to be carried by neural channels in the parvocellular pathway and to be encoded in an opponent manner, while other, non-parvocellular, spectrally non-opponent channels are thought to play no part in colour vision. But is the parvocellular pathway the only way that colours can be discriminated in human vision? We studied two patients with cerebral achromatopsia, who lack conscious colour perception but are nevertheless able to make use of colour information. In particular, we investigated whether, in these patients, colour discrimination is mediated by the parvocellular pathway. RESULTS: The achromatopsic patients carried out a forced-choice colour- and luminance-discrimination task, and showed clear evidence of unconscious colour processing, consistent with previous studies. We added different types of luminance noise to see when this unconscious colour information could be masked. The results of the colour-discrimination-with-noise and the brightness-non-additivity experiments showed a double-dissociation between patients. This indicates that, in one patient, unconscious colour discrimination may be subserved by a spectrally non-opponent mechanism, which does not have the characteristics of the parvocellular pathway and which is responsive to fast flicker. Spectral sensitivity, contrast sensitivity and motion perception experiments confirmed that this patient lacks a working opponent parvocellular system. The second achromatopsic patient showed evidence of a residual parvocellular system. CONCLUSIONS: Our results show that chromatic discrimination need not be mediated by neural mechanisms, the parvocellular system in particular, normally assumed to subserve conscious colour perception. Such discrimination may be mediated by a neural subsystem which responds to fast flicker, is spectrally non-opponent, and supports normal motion perception.

Aged↗
PubMed1998

A maximum motion technique for assessment of color vision defects.

Several luminance-matching methods, such as flicker fusion and the minimum motion technique (MMT), are capable of detecting certain forms of abnormal color vision. We present evidence that the heterochromatic fusion nystagmus (HFN) luminance matching technique can discriminate among normal trichromats, protanopes, and deuteranomals. The HFN luminance matching technique has the advantage that it provides a positive indication of isoluminance (maximization of motion) as opposed to the MMT and flicker fusion methods, which indicate isoluminance by the minimization of motion and flicker, respectively. We tested 16 normal trichromats, 6 protanopes, and 4 deuteranomals with the HFN technique. Results indicate that HFN is a useful tool for examining color vision. Because the HFN stimulus elicits reflexive eye movements (optokinetic nystagmus) that follow the apparent motion of the stimulus, HFN luminance matching will be particularly useful in animal and infant research, where other color vision tests are difficult to implement.

Adolescent↗
PubMed1998

A modified card procedure for measuring human infant color vision.

To improve test efficiency, we modified our previously introduced contrast/color card test by including a patterned test stimulus and reducing the number of stimuli in both experimental phases. Compared with the prototype, completion rate improved substantially (79 vs. 37%) but test time decreased only modestly (19 vs. 21 min). Achromatic contrast discrimination improved threefold (mean, 0.06 vs. 0.20 log units), but the percentage of 2-month-old infants who discriminated (from gray) 660-nm red (86 vs. 80%) and 580-nm yellow (52 vs. 55%) was consistent. In addition, 48% discriminated 574-nm yellow-green. Moreover, because 88% of infants' failures included the respective adult brightness/luminance match, a small range of relative luminances is adequate for testing infant color vision.

Color Perception↗
PubMed1992

Screening of diabetics who read incorrectly colour-dependent glucose test-strips.

Forty-eight diabetic patients (82 eyes) were examined with four different colour vision tests and one blood glucose strip-test. The ages of the patients varied from 23 to 65 years (mean 44.3 years +/- 11.4, SD), the duration of diabetes from 13 to 41 years (mean 25.8 +/- 6.2), and the visual acuities from 0.2 to 1.0 (mean 0.8 +/- 0.2). Of the eyes, 77 had had photocoagulation, 25 had small peripheral lens opacities, and 55 had slight background retinopathy. The colour vision tests were: the Standard Pseudoisochromatic Plates part 2 (SPP2), the Lanthony Tritan Album, the Farnsworth Panel D 15 test and the box III of the Farnsworth-Munsell 100 hue (FM 100) test. The blood glucose test was Haemo-Glukotest 1-44. Of the 82 eyes, 38 incorrectly saw Haemo-Glukotest strips. The SPP2 test found 89% of the eyes, the Tritan Album 55%, the Panel D 15 71%, and the box III of the FM 100 test 76%. The strips were correctly interpreted in 44 of the eyes. However, 36% of them failed the SPP2, 16% the Tritan Album, 11% the Panel D 15 test and 18% the box III of the FM 100 test. The Panel D 15 test and the box III of the FM 100 test would be useful in screening those diabetics who cannot correctly interpret the colour-dependent glucose test-strips and would need a blood sugar meter for their blood glucose level testing.

Adult↗