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Biomedical subjects

K Kitahara

Publications and source records attributed to K Kitahara.

At least 91 records · Page 5Linked to original sources
PubMed1983

Classical tritanopia.

1. A subject who has suffered from central serous chorio-retinopathy in his left eye noticed differences in the colour of a given light as perceived by each eye alone. Standard screening tests (colour order and colour matching) indicated a tritan defect in the left eye; the right eye was normal on these tests.2. The subject was dichromatic in his left eye, trichromatic in his right. The left-eye distimulus colour-matching functions, spectral luminosity, and wave-length discrimination functions were indistinguishable from corresponding data for congenital tritanopia. Comparable right-eye data were normal.3. Spectral dichromatic colour matches were invariant under changes of intensity and under addition of a common light to both halves of the field. (Grassmann's laws of linearity are satisfied.)4. Increment threshold versus intensity (t.v.i.) curves for a blue (481.9 nm) test on a yellow background yielded the normal three branches (for Pi(4)(mu), Pi(1)(mu) and Pi(3)(mu) respectively) in the trichromatic eye. In the dichromatic eye a single mechanism was found. It had the field sensitivity of Pi(4)(mu) whether measured with the blue, or with a violet (429.5 nm) test. No trace of Pi(3)(mu) or Pi(1)(mu) was ever discovered in the tritanopic eye. Both are normal in the trichromatic eye.5. The field sensitivities of Pi(4), Pi(5) and Pi(3) of the normal eye are well fitted by linear combinations of the spectral colour-matching functions of the trichromatic eye. Pi(4) and Pi(5) of the dichromatic eye are well fitted by linear combinations of the tritanopic matching functions.6. Colour matches made by the trichromatic eye do not match when viewed by the tritanopic eye, almost certainly because the ocular media of the two eyes have wave-length-dependent differences in absorption. For the largest difference (430 nm) the trichromatic eye transmits about 2.2 times more light than its fellow. When allowance is made for these differences, the field sensitivities of Pi(4) and Pi(5) of the two eyes do not differ. The field sensitivities of Pi(4) and Pi(5) of the normal eye, on the other hand, differ significantly from those of the average spectra obtained on four normal trichromats by Stiles, in a way that cannot be attributed to differences in transmittance of ocular media.7. It is concluded that classical (or acquired) tritanopia is not distinguishable in its manifestations from congenital tritanopia; furthermore, tritanopia can be regarded as a reduced form of normal trichromacy, once allowances are made for absorption of the ocular media and for variations among normal trichromats.8. Despite extensive search no evidence could be uncovered which might exclude the hypothesis that the colour vision in tritanopia depends exclusively upon absorption in only two foveal cone pigments, one long-wave-absorbing and one medium-wave-absorbing.

Adult↗
PubMed1983

Perception of colour in unilateral tritanopia.

The unilateral tritanope described in the previous paper (Alpern, Kitahara & Krantz, 1983) was able to match every narrow-band light presented to his tritanopic eye with lights from a tristimulus colorimeter viewed in the adjacent field by the normal eye. In two regions of the spectrum (called isochromes) physically identical lights appeared identical to the observer's two eyes. One isochrome was close to 'blue' for the normal eye, the other was in the long-wave spectral region seen by the normal eye predominantly as 'red'. Between these isochromes the normal eye required less than spectral purity to match, dropping to near zero purity at 560-570 nm. A mixture of the two isochromes that appeared purple to the normal eye appeared neutral to the tritanopic eye. Hence dichoptic matches grossly violate Grassmann's additivity law. For the normal eye colour naming conformed to typical normal results. For the tritanopic eye the results were coherent with those found by dichoptic matching: the spectrum was divided into two regions by the achromatic neutral band. To the short-wave side, only the colour names 'blue' and 'white' were ever used. To the long-wave side the predominant colour names were 'red' and 'white' with some 'yellow'. Spectral lights appeared neither 'red-blue' nor greenish. Surrounding the test with an annulus either 430 nm, 650 nm, or a mixture of these, fails to induce any greenish appearance, although the achromatic band shifted in the expected directions. It is concluded that there must be exactly three functionally independent, essentially non-linear central codes for colour perception, and that these codes are different from those suggested in existing theories of colour perception.

Adaptation, Physiological↗
PubMed1983

The directional sensitivities of the Stiles' colour mechanisms.

Field sensitivities of the three IIj (j = 3, 4, 5) mechanisms of Stiles were measured for monochromatic backgrounds of different wave numbers (mu)-1 traversing the eye through different points (r) displaced along a horizontal chord through the centre of the entrance pupil. Each mechanism shows an insensitivity to the direction of retinal incidence of short-wave backgrounds not previously described. The spectral densities of the centre-most part of the lens and of the macular pigment were measured on this eye. With reasonable assumptions the former allowed for correction at the receptor level of the directional sensitivity; together with the latter it allowed correction for the spectral sensitivity as well. No correction for the attenuation of the high spatial frequencies of the background as it traversed the pupil at different r was needed. The anomalies of section 2 (above) disappear after correction for losses in the eye media. After these corrections, for every mu and r, the results are well described by the parabola 'tentatively' suggested by Stiles (1939) for each mechanism, allowing only a small amount of variance attributable to experimental imprecision alone. Each mechanism is most sensitive to backgrounds going through essentially the same point of the pupil, independent of background. This result is inconsistent with a qualitative explanation of the 'hue shift' suggested by Safir, Hyams & Philpot (1971). The field sensitivity spectra for backgrounds traversing the pupil at this most effective point and at the 3.5 mm margin, are the data needed to predict this observer's brightness and colour matches of monochromatic lights passing through the entrance pupil at these two points according to a unified theory of the two Stiles-Crawford effects. In the following paper these predictions are quantified and confronted with results of the matching experiments (Alpern, Kitahara & Tamaki, 1982).

Adult↗
PubMed1983

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

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. One observer was also the subject of the preceding paper (Alpern & Kitahara, 1983) in which the field sensitivities of his foveal IIj(mu) (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 IIj mechanisms for normal incidence. 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 IIj(mu) mechanisms. The Stiles-Crawford colour effect data contradict the expectations of the unified theory applied with these same IIj(mu) mechanisms. Either II3(mu) is not a valid operational definition of the action spectrum of his short-wave sensitive photoreceptors or at least one assumption of the unified theory is false.

Color Perception↗
PubMed1983

The directional sensitivity of retinal rods.

Rod field sensitivity, 10-S(r) (i.e. the reciprocal of the radiance of a background required for 10-fold elevation of rod threshold) was measured for monochromatic backgrounds traversing the pupil at various points (r) on three subjects. The wave-length dependency of the directional sensitivities of the three foveal cone mechanisms of the principal subject have been reported previously (Alpern & Kitahara, 1983). Rods, as cones, are less sensitive to obliquely incident, than to normally incident backgrounds. At the pupil margin (4 mm) the effect is between 0.368 and 0.976 log10 units smaller for rods. After correction for losses by corneal reflexion and by absorption in the lens, S(r) for rods is reasonably described by the parabolic equation used by Stiles (1937) to quantify the directional sensitivity of cones. The small effect for rods precludes a description as consistently precise as this equation provides for cones. The steepness of the parabolic curve best fitting the directional sensitivity data of the rods of the principal subject was independent of background wave number. For a second subject, whose rods are supposed to be smaller, it was directly proportional to the square of that wave number. The latter is the expectation if the directional sensitivity of this subject's rods were determined by principles outlined in the diffraction theory of Simon (1970).

Humans↗