Foveal increment thresholds in normal and deutan observers

Disease recognition in philodendron leaf using image processing technique

Numerous disease recognition techniques are available to identify diseases in plant leaves. Assignment of spherical polar coordinate treated equivalent to hue, saturation, and intensity helps for disease recognition in Philodendron leaf which was identified as specks. Black vision, white vision, and color vision for the eye are possible with photopigments present in rods and cones in the retina. The highlight of this paper is converting the Philodendron leaf in natural color to grayscale and applying the technique of hue, saturation, and value to the gray image. Then running iteration for the double-sized image by allowing for the simultaneous recognition of the diseased part helps for the identification of the spots present in the leaf. This focuses specks on a brighter scale.

The visual photopigments of simple deuteranomalous trichromats inferred from color matching

Deuteranomalous trichromacy is the most common form of inherited color-vision deficiency. A modern description of its cause is a single abnormality: the normal middle-wave cone photopigment (M) is replaced by a shifted middle-wave pigment (M) that is shared by all deuteranomalous trichromats. This explanation, however, fails to account for the individual differences in color vision observed even within the sub-group of deuteranomals with good chromatic discrimination. An ensemble of color matches is used here to test whether these individual differences reflect differences in the wavelength of peak sensitivity (lambda max) of individual deuteranomals' cone photopigments. The results show variation in both the lambda max and the effective optical density of their cone pigments. The individual differences found in lambda max are in accord with recent molecular biological research that shows individual differences in the genes thought to encode deuteranomalous photopigments.

Temporal integration of the pi 1/pi 3 pathway in normal and dichromatic vision

Stiles' pi 1 and pi 3 mechanisms are thought to reflect adaptation events at two sites in a single pathway, the first site controlled by the short-wavelength cones alone, the second site controlled by opposing signals from these cones vs the other cone classes. We examined this pathway's temporal integration under conditions that yield the full gamut of possible adaptation states at the two sites. Critical duration of the pi 1/pi 3 pathway was always about 200 msec. In addition, we examined the pi 1 and pi 3 mechanisms of dichromatic vision. Our results suggest that protanopic and deuteranopic vision are characterized by a pi 1/pi 3 pathway similar to that in normal color vision.

Sensitivity losses in a long wavelength sensitive mechanism of patients with retinitis pigmentosa

the foveal vision of certain patients afflicted with retinitis pigmentosa may be mediated solely by a long wavelength sensitivity (lws) mechanism, because (1) increment threshold data could always be fitted to a single template curve with unity slope, (2) test and field sensitivities differ only by a proportionality constant over the visible spectrum, (3) intense background fields have additive (quantum catch) effects on thresholds, and (4) wavelength differences of bipartite foveal stimuli could not be distinguished. Both test and field sensitivities were appreciably lower than the lws sensitivity values for unaffected deuteranopes. The action spectrum was similar (but not identical) to estimates of the erythrolabe absorption spectrum. The results provide a better understanding of the photopic vision of patients with retinitis pigmentosa and further evidence that their effective optical density of residual cones is reduced.

An anomaly in the response of the eye to light of short wavelengths

Adaptation of the human eye to long-wavelength light leaves it insensitive to short-wavelengths: a blue flash that is visible in the presence of a yellow adapting field may remain invisible for several seconds after the field has been turned off (see experiment 1 and Appendix). This ‘transient tritanopia’ occurs for a large range of adapting intensities, but is abolished if the adapting field is very bright (experiment 2). The loss of sensitivity is primarily confined to the blue-sensitive cone mechanism (experiments 2 a , 3 and 4 ; and Appendix) and can be produced by small attenuations of the adapting field (experiment 5). It occurs in both foveal and parafoveal vision (experiment 6) but is absent when adapting and test stimuli are presented to opposite eyes (experiment 7). It was found in a protanope (experiment 9 a ) and, in a modified form, in a deuteranope (experiment 9 b ). No differences in sensitivity were found for blue flashes presented in the light and dark phases of a field flickering at a rate above the fusion frequency (Appendix). The sensitivity of the blue-sensitive mechanism of the eye appears to be controlled not only by quanta absorbed by the blue receptors but also by a mechanism with a different spectral sensitivity

Colour vision in blue-cone 'monochromacy'

1. 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 (pi(0)) 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 pi(0) and pi(1). The chromaticity co-ordinates have been calculated according to the convention of W. D. Wright and compared to the results predicted from pi(0) and pi(1). 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 pi(0), pi(1) 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 pi(1), the second to the pi(0) cones.8. Using a broad band blue gelatin filter in the measuring light of the 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 1.0 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.