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PubMed1984

[Erythropsia in a patient with lens implant. Physiologic and electrophysiologic study].

A case of snow erythropsia is described in a patient with pseudophakia (Binkhorst four loop len). Symptoms of the condition lasted a week and allowed us to define psychophysic and electrophysiological findings. Morphoscopic night threshold was raised (0,28 b/hm 2). Resistance to glare was very low. In the study of colour vision, answers for Beyne's lantern lights were: pink orange for white; grey for blue; purple for red; red for orange; white for green. Ishihara and Farnsworth tests showed a defect of the red-green type. With the Nagel anomaloscope the matching of colours was normal (Rayleigh match). Electrophysiological study showed a low value of the standing potential of the eye and a normal electroretinogram. It seems that the colour defect in erythropsia is a glare phenomenon due to high luminance.

Adaptation, Ocular↗
PubMed1983

The effect of reduced viewing time on colour vision in normal subjects and those with abnormal ocular conditions.

The effect of restricting viewing time to 3.75 ms in normal subjects is to produce a tritan-like colour response on the City University colour vision test. This response pattern is consistent and is repeatable for standard illuminant C at 600 lx. Supplementary tests suggest that the effect is due to a defect of the blue/yellow opponent system rather than a true tritan defect. The same test when repeated on subjects with amblyopia or retinal pathology provides different results which may aid in the differential diagnosis of some visual disorders.

Amblyopia↗
PubMed1984

What can colour thresholds tell us about the nature of the underlying detection mechanisms?

Two-colour increment thresholds, which have traditionally been analysed in terms of pi-mechanisms, were subjected here to a different form of analysis. Detection thresholds were measured for monochromatic test flashes and 10 bichromatic mixture combinations containing various proportions of two out of the five primaries: white, blue, green, yellow and red. The 1 degree, 0.5-s duration, foveal flashes appeared on a 1000-td blue background. All the thresholds were simultaneously fitted by assuming probability summation from a limited number of independent linear mechanisms. The assumption of two detection mechanisms provided a reasonable fit for all the bichromatic mixture thresholds. One mechanism received a positive contribution from both M and L cone types, whereas the other received an excitatory contribution from the L cone type, and an inhibitory contribution from the M cone type. The predictive power of the model was tested and compared to the pi-mechanism concept by fitting a spectral-sensitivity curve measured under identical conditions. It was concluded that parts of pi-mechanism curves probably reflect the responses of colour-opponent processes rather than those of single cone types.

Color Perception↗
PubMed1980

The McCollough effect in rhesus monkey.

After viewing red vertical stripes and green horizontal stripes, the eye subsequently views white vertical stripes as greenish and white horizontal stripes as pinkish. It has been theorized that this phenomenon, known as the McCollough effect, is related to long-tern adaptation of cells tuned for both color and orientation. Such cells have been found in the visual cortex of the rhesus monkey. We asked whether rhesus monkeys, like man, experience a McCollough effect. Two humans and two rhesus monkeys were adapted by requiring them to fixate a spot moving slowly across alternating horizontal and vertical gratings of complementary color. Following adaptation, a test grating whose color changed from red to green or green to red was presented. Humans and monkeys were instructed or trained to release a response lever during the interval that the grating was white. After adaptation, there were orientation-specific changes in all four subjects' responses as would be predicted if both man and monkey were experiencing a McCollough effect.

Adaptation, Physiological↗