1 Cone Monochromatism

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SUMMARY1. Atypical (blue cone) monochromats show two action spectra when tested by the increment threshold method of Stiles with' central' fixation. One spectrum peaks near 450 nm and has the spectral characteristics of normal blue cones. The other resembles rhodopsin (r0) modified slightly by photostable macular pigment.2. Under some circumstances such observers are dichromats. There is a neutral point (matched to Illuminant 'C') in the neighbourhood of 460-470 nm.3. The spectral colour matching functions using two primaries have been measured on three such subjects. They can be fit reasonably well, although imperfectly, by linear combinations of oro and nr1. The chromaticity co-ordinates have been calculated according to the convention of W. D. Wright and compared to the results predicted from no and or1. The comparison suggests that part of the imperfections of the colour matching function fit is due to prereceptor differences (e.g. macular pigment) between the blue-cone monochromats and the hypothetical sTOp, iT observer.4. Colour matches made at high light levels continue to hold when the intensity of the field is reduced below the cone threshold.5. Therefore one of the visual pigments participating in the colour matches has an action spectrum which is not measurably different from that of the rod pigment rhodopsin.6. Increment threshold measurements show that the mechanism which has the rhodopsin action spectrum has the directional sensitivity of cones, not rods.7. Blue test threshold during dark adaptation after a full bleach follow a bipartite exponential recovery curve. The first exponential has a time constant of 1 min, the second 2 min. By comparing these curves to the increment thresholds it is possible to relate the first to the oTr, the second to the 7T0 cones.8. Using a broad band blue gelatin filter in the measuring light of the M. ALPERN AND OTHERS retinal densitometer and studying the same retinal region tested in 7 it is possible to follow the regeneration of a pigment after a full bleach which has an exponential recovery with a time constant of 10 min. With a yellow green filter in the measuring light the exponential recovery observed after a full bleach has a time constant of 2-0 min. 9. One of the two visual pigments participating in the colour matches resides in receptors which have the action spectrum, the directional sensitivity and probably the dark adaptation curve of normal blue cones.10. The other resides in receptors which have the action spectrum of normal rods but the directional sensitivity and the dark adaptation curve of normal red and green cones.

Section: Colour Vision In Blue-cone 'Monochromacy' 225mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Colour vision in blue‐cone ‘monochromacy’

Alpern¹,

Lee²,

Maaseidvaag³

et al. 1971

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“…While it can not be said that there is general agreement among authorities as to the most valid operational definition of human long-and medium-wave sensitive cone action spectra, there are strong converging lines of evidence from experiments as diverse as psychophysical observations on short-wave cone monochromacy (Alpern, Lee & Spivey, 1965;Alpern, Lee, Maaseidvaag & Miller, 1971;Alpern, 1974), on transient changes in backgrounds (Stiles, 1949;Mollon & Polden, 1975Stiles, 1978; Augenstein & Pugh, 1977;Pugh & Mollon, 1979;Mollon, 1982), on two colour threshold vs. wave-length curves (Wald, 1964) and from in situ microspectrophotometry of the visual pigments of individual short-wave sensitive cones (Bowmaker & Dartnall, 1980) all pointing to H3(u) as the most valid operational definition available for the action spectrum of human short-wave sensitive cones. Before reaching such a striking conclusion alternative interpretations of the contradiction illustrated in Fig.…”

Section: Introductionmentioning

confidence: 99%

The dependence of the colour and brightness of a monochromatic light upon its angle of incidence on the retina.

Alpern¹,

Kono²,

Tamaki³

1983

SUMMARY1. The changes in brightness and colour of a monochromatic test light as its angle of incidence on the retina was changed from normal (pupil centre traverse) to oblique (3 5 mm temporal pupil traverse), was measured by matching it with three normally incident primaries. Results on two normal trichromats were generally in accord with published data on the Stiles-Crawford intensity and colour effects.2. One observer was also the subject of the preceding paper (Alpern & Kitahara, 1983) in which the field sensitivities of his foveali1(,u) (j = 3, 4, 5) mechanisms for normally, and obliquely, incident backgrounds were reported. For normal incidence, the colour matching functions are in rough accord with expectation if the action spectra of the three cone mechanisms, which provide the photoreceptor basis for his trichromacy, were the same Hi mechanisms for normal incidence.3. A unified theory is developed for both Stiles-Crawford intensity and colour effects, assuming that the same visual pigments in the same set of univariantly signalling cones absorbs both the normal incident primaries and the obliquely incident test. Given no free parameters for curve fitting, the Stiles-Crawford intensity effect data are in reasonable agreement with the theory if the photoreceptor basis of these matches were the normally and obliquely incident II(,u) mechanisms.4. The Stiles-Crawford colour effect data contradict the expectations ofthe unified theory applied with these same Hl1(l) mechanisms. Either H3,() is not a valid operational definition ofthe action spectrum ofhis short-wave sensitive photoreceptors or at least one assumption of the unified theory is false.

“…Consequently, these findings have been interpreted as indicating that the blue cones are spatially organized rather differently than the other two colour mechanisms. In particular, it has been argued that the blue cone mechanism has a lower visual acuity (Stiles, 1953;Brindley, 1954; Green, 1968), greater spatial summation (Brindley, 1954) and reduced contrast sensitivity (Green, 1968 Alpern, Lee & Spivey (1965) have shown that this photopic luminosity curve which peaks at A = 440 nm is the same as the spectral sensitivity curve of the blue mechanisms of the normal eye as measured by Stiles (1959) using two colour increment thresholds. In addition, the above authors found that the absolute cone threshold of the blue cone monochromat was the same as that of the 7Tr cone mechanism of the normal fovea.…”

Section: Introductionmentioning

confidence: 99%

Visual acuity in the blue cone monochromat

Green¹

1972

SUTMMARY1. To isolate the blue cones of the normal eye, blue sine-wave gratings were superimposed on a bright yellow background. Threshold contrasts for resolution of the gratings were then determined.2. Under these conditions visual acuity for high contrast gratings on four normal subjects was on the average 0-31 min-l. This is about a factor of 6 lower than grating acuity under optimal conditions. 3. The contrast sensitivity of two subjects who lack the normal red and green receptor mechanisms was measured using blue sinusoidally modulated gratings. Visual acuity was found to be greatly reduced from normal. The low acuity of these individuals is due to both a reduction in contrast sensitivity and a reduction in resolution.4. The spatial resolving characteristics of these subjects resembles the vision of the normal eye under conditions which isolate the blue sensitive mechanisms.5. The vision of the cone monochromat differs significantly from that of the more typical rod monochromat. The rod monochromat has even lower acuity than the blue cone monochromat for high contrast gratings but has much greater contrast sensitivity for gratings of low spatial frequency.