Long-wavelength Sensitive Cone Research Articles

Redness from short-wavelength-sensitive cones does not induce greenness

According to opponent-colors theory, a reddish surround induces greenness in a central test field. Color-appearance measurements verify this with a long-wavelength reddish surround (660 nm) but not with a short-wavelength reddish surround (440 nm). Surprisingly, a short-wavelength reddish surround shifts the appearance of a test toward redness. Four possible explanations are: (1) stray light from the short-wavelength reddish surround falls in the test area; (2) receptoral sensitivity changes over whelm induced greenness from the surround; (3) a neural process of assimilation, rather than contrast, to the surrounding light; (4) short-wavelength-sensitive (S) cones do not contribute to induced redness/greenness. Chromatic cancelation experiments confirm the fourth explanation. There was no change in induced redness/greenness when quantal absorption by only S cones in the surround was varied by 30-fold (using tritanopic metamers), even though varying stimulation of S cones strongly affected the color appearance of the surround. The redness induced by a short-wavelength surround is accounted for by opponent chromatic induction mediated by only middle- and long-wavelength sensitive cones.

Foveal cone detection statistics in color-normals and dichromats

We measured for six male observers, the psychometric functions for the detection of two simultaneously presented points of light. The test stimuli were two 1 min point sources separated by 17 min arc, and pulsed for 0.5 msec. The stimuli varied in wavelength from 500 to 620 nm. The psychometric functions were fit with a model that assumes ideal detection and the following properties: (1) Poisson-distributed quantal absorptions; (2) binomial sampling of foveal long-wavelength-sensitive (LWS) and middle-wavelength-sensitive (MWS) cones; (3) independent responses of the LWS and MWS cones; and (4) the Smith-Pokorny fundamentals for cone spectral sensitivies. Based on χ 2 fits to the psychometric functions for detecting neither, one or both of the two-point stimuli presented, estimates were derived for the minimum quantal catch by a single cone for detection ( C), the number of effective cones illuminated by a point stimulus at threshold ( N) and the proportion of central foveal cones of the LWS type ( P L ). Three observers were color-normal, two were protanopes and one was a deuteranope. A second deuteranope was included in the design but his data were too unreliable for an unambigous solution. The estimated quantal requirement C was consistently near 5 (4–6), and the effective number of illuminated cones always was 1 or 2. The plausible range of P L (98% confidence interval) for the color-normal observers was 0.48–0.68 (observer YY), 0.76–0.90 (observer MW) and 0.77–0.95 (observer DF). The best fitting P L solution for these observers were 0.61, 0.82 and 0.88, respectively. These were comparable to the values obtained from flicker photometric data. The best P L value for each of the protanopes was 0.00 and for the deuteranope the best P L value was 0.98.

Psychophysical measurement of spectral sensitivity and color vision in red-light-reared tree shrews ( Tupaia belangeri)

The role of the spectral lighting environment on the post-natal development of spectral sensitivity and color vision was studied in tree shrews ( Tupaia belangeri) that were born and reared to adulthood in cyclic red light. Normal tree shrews are dichromats, possessing short-wavelength-sensitive (SWS) and long-wavelength-sensitive (LWS) cone receptors and a small population of rods. Red-lightrearing (RLR) produced differential stimulation of the cone types by effectively eliminating photic stimulation of the SWS cones, without depriving the LWS cones. Spectral sensitivity and color vision were measured behaviorally for RLR shrews and normal shrews under different ambient light levels. Spectral sensitivity functions were deutan-like, exhibiting maxima at ca 450 and 550 nm and a minimum at 510 nm. No significant differences in spectral sensitivity were observed between RLR and control animals. Furthermore, all animals demonstrated deutan-type dichromatic color vision evidenced by their ability to discriminate monochromatic lights from equally-bright achromatic lights except for a “neutral point” near 505 nm. These results demonstrate that a population of functional SWS cones survived the lack of post-natal photic stimulation. However, RLR shrews differed from controls in that they were poorer at making chromatic/achromatic discriminations. While no severe disorganization of color vision was evident, the poorer discrimination displayed by the RLR animals is likely the result of changes in post-receptoral visual mechanisms.

Autosomal Dominantly Inherited Macular Dystrophy with Preferential Short-Wavelength Sensitive Cone Involvement

We found an apparently inherited tritan-like color vision defect in five members of a family, spanning three generations. The defect was associated with mild macular pigmentary changes, poor foveolar reflexes, or slightly reduced visual acuity in four of the affected individuals. The inheritance pattern appeared to be autosomal dominant. Results of various color vision tests indicated preferential involvement of the short-wavelength sensitive cone system, with relative preservation of the middle- and long-wavelength sensitive cone systems. Both anomaloscope testing with larger (8-degree) fields and short-wavelength sensitive electroretinography indicated some short-wavelength sensitive cone system involvement beyond the central macula in the three affected individuals on whom testing was performed. The condition appeared to be a familial macular dystrophy with preferential short-wavelength sensitive cone involvement. The abnormal macular findings and mild reduction in visual acuity distinguish this condition from congenital tritanopia; the normal optic disks distinguish it from autosomal dominant optic atrophy.

Cone mechanisms and their colour-opponent interaction in monkeys and cat.

Cone mechanisms and colour opponency were investigated in 108 recordings from tonic ganglion cells of the rhesus monkey retina and 265 recordings from ganglion cells of the cat retina. Colour-opponent cells input from short and longer wavelength sensitive cones can be found in both species in about equal proportions (6-8%). Although cells with opponency between middle and long-wavelength sensitive cones are very common in monkey (49%), they are rare in the cat (4%); usually the opponency of the latter can only be detected with strong chromatic adapting lights suppressing the dominant mechanism, while in monkey colour opponency is usually revealed under neutral adapting conditions. These differences between both species in processing chromatic stimuli can help to explain certain types of colour vision deficiencies in man.

Dark adaptation of the long-wavelength sensitive cones

Long-wavelength sensitive (L) cone dark adaptation curves were measured with a 10-msec, 20′ v.a., 650 nm test flash and a moderate intensity adapting field. When the 650 nm and 500 nm fields were equated for the L cones, the dark adaptation curve fell faster for the 500 nm field than for the 650 nm field. Over the range of adapting lights used, no adjustment of the intensities of the two fields made their dark adaptation curves similar. When 500 nm light was added to the 650 nm field, dark adaptation was faster. Visual sensitivity is not regulated by any single photoreceptor type in this experiment.

Classification of complete and incomplete autosomal recessive achromatopsia.

We studied color vision in 32 patients with autosomal recessive achromatopsia. Color matching revealed complete achromatopsia (rod monochromasy) in ten patients (Group I) and incomplete achromatopsia in the remaining twenty-two patients. Amongst the incomplete achromats, were three groups distinguishable by their color matching. Patients in Group II were dichromats; their color matches were mediated by rods and MWS (middle-wavelength sensitive) cones. Patients in Groups III and IV were trichromats. Color matches of patients in Group III were mediated by rods, LWS (long-wavelength sensitive) cones and MWS cones. Group III patients showed no evidence of SWS (short-wavelength sensitive) cones. Color matches of patients in Group IV were mediated by rods, LWS cones and SWS cones; color matching did not reveal MWS cones.

Spectral sensitivity of the foveal cone photopigments between 400 and 500 nm

A comparison was made between the shape of the iodopsin absorption spectrum calculated for appropriate optical density to (1) a set of König-type fundamentals in which the tritanopic copunctal point was set on the alychne and (2) data obtained from red-green dichromats using high intensity heterochromatic flicker procedures which eliminated participation by the short-wavelength sensitive mechanism. The transformation of normal color mixture data resulted in two fundamentals which gave a reasonable prediction of the tritanopic coefficients. The dichromatic HFP data corrected individually to average macular pigment agreed with their respective fundamental above 430 nm. The HFP data and transformation were converted to a retinal level, quantized and plotted as a function of wavenumber. For the middle-wavelength-sensitive mechanism, the protanopic HFP data and its König-type fundamental agreed with the predicted absorption spectrum above 460 nm. The deviations below 460 nm had the shape of the lens absorbance curve. For the long-wavelength sensitive mechanism, the deuteranopic data and its König-type fundamental agreed with the predicted absorption spectrum above 520 nm. The deviations below 520 nm could not be fit solely by the lens absorbance factor used above, but needed in addition, added macular pigment of optical density at 460 nm of ca. 0.12. This result was checked by calculating predicted tritanopic coefficients for the two predicted absorption spectra, when the long-wavelength sensitive spectrum was screened by a slight amount (o.d. of 0.12 at 460 nm) of macular pigment. These predicted coefficients agreed with the Wright tritanopic coefficients. We conclude (a) that the shape of the iodopsin absorption spectrum provides a reasonable basis for computation of absorption spectra of the middleand long-wavelength sensitive cone pigments and (b) that long-wavelength sensitive cones of deuteranopes. tritanopes, and normal trichromats are subject to a selective screening filter of optical density at 460 nm of 0.12 and spectral shape similar to macular pigment.

Spectral sensitivity of color-blind observers and the cone photopigments

A comparison was made between Dartnall's standard shape for visual pigments and the spectral sensitivities of the short-, middle-, and long-wavelength sensitive cone receptor mechanisms of man Data from blue monocone monochromats, protanopes, and deuteranopes were chosen as reliable estimates of each of the three classes of cone sensitivities The shortwavelength sensitive mechanism fits the standard shape The middle- and long-wavelength sensitive mechanisms have the same shape on a wavenumber axis but do not fit Dartnall's standard shape for visual pigments The shape of the middle- and long-wavelength sensitive mechanisms also describes some other published absorption spectra of visual pigments with λ max > 520 nm , notably the lodopsins found in birds.