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Yes / We used triple silent substitution stimuli to characterize human S-cone electroretinograms (ERGs) in normal trichromats. Short-wavelength-cone (S-cone) ERGs were found to have different morphological features and temporal frequency response characteristics compared to ERGs derived from L-cones, M-cones, and rod photoreceptors in normal participants. Furthermore, in two cases of retinal pathology, blue cone monochromatism (BCM) and enhanced S-cone syndrome (ESCS), S-cone ERGs elicited by our stimuli were preserved and enhanced, respectively. The results from both normal and pathological retinae demonstrate that triple silent substitution stimuli can be used to generate ERGs that provide an assay of human S-cone function. / Deutsche Forschungsgemeinschaft (DFG) (KR1317/13-1); Bundesministerium für Bildung und Forschung (BMBF) (01DN14009)

Yes / Edge detection plays an important role in human vision, and although it is clear that there are luminance edge detectors, it is not known whether there are chromatic edge detectors as well.We showed observers a horizontal edge blurred by a Gaussian filter (with widths of r ¼ 0.1125, 0.225, or 0.458) embedded in blurred Brown noise. Observers had to choose which of two stimuli contained the edge. Brown noise was used in preference to white noise to reveal localized edge detectors. Edges and noise were defined by either luminance or chromatic contrast (isoluminant L/M and S-cone opponent). Classification image analysis was applied to observer responses. In this analysis, the random components of the stimulus are correlated with observer responses to reveal a template that shows how observers weighted different parts of the stimulus to arrive at their decision.We found classification images for both luminance and isoluminant chromatic stimuli that had shapes very similar to derivatives of Gaussian filters. The widths of these classification images tracked the widths of the edges, but the chromatic edge classification images were wider than the luminance ones. These results are consistent with edge detection filters sensitive to luminance contrast and isoluminant chromatic contrast. / Royal Society Travel Grant IE130877 and in part by Canadian Institutes of Health Research (CIHR) grant MOP-10819

The work in this thesis is concerned with examining the retinal and cortical contributions to human trichromatic colour vision. Chromatic processing at the cortex level was examined using visual evoked potentials (VEPs). These responses were elicited by chromatic spot stimuli, which were manipulated in order to selectively activate the chromatic processing system. Chromatic processing at the retinal level was examined using the electroretinograms (ERGs) for which cone isolating stimuli were used to assess the nature of L and M cone inputs to cone-opponent mechanisms. The results from the VEP experiments suggest VEP morphology is dependent upon 1) chromatic and or luminance contrast content of the stimulus, 2) stimulus size, and 3) extent to which the chromatic stimulus activates either the L/M or S/(L+M) opponent mechanism. The experiments indicate that chromatic stimulation is indexed by large N1 component and small offset responses. Optimal stimulus size for chromatic isolation is 2-4 ° along L/M axes and 6° along S/(L+M) axis. From the ERG experiments, It has been shown that the low (12Hz) and high (30Hz) temporal frequency flickering stimuli can isolate the chromatic and luminance processing mechanisms in the retina. For low temporal frequency ERGs, the L:M ratio was close to unity and L/M phase difference was close to 180°. For high temporal frequency ERGs, the L:M ratio was more than unity and L/M phase difference was close to 90°. In addition to this, the variation in L:M ratio across the retinal eccentricity was also examined. These results suggest, for the chromatic processing, L:M ratio is close to unity independent of retinal eccentricity and individuals. For the luminance processing, L:M ratio is more than unity and depends upon the region of the retina being stimulated. These findings indicate the maintenance of cone selective input for the chromatic processing across the human retina.

The work in this thesis is concerned with examining the retinal and cortical contributions to human trichromatic colour vision. Chromatic processing at the cortex level was examined using visual evoked potentials (VEPs). These responses were elicited by chromatic spot stimuli, which were manipulated in order to selectively activate the chromatic processing system. Chromatic processing at the retinal level was examined using the electroretinograms (ERGs) for which cone isolating stimuli were used to assess the nature of L and M cone inputs to cone-opponent mechanisms. The results from the VEP experiments suggest VEP morphology is dependent upon 1) chromatic and or luminance contrast content of the stimulus, 2) stimulus size, and 3) extent to which the chromatic stimulus activates either the L/M or S/(L+M) opponent mechanism. The experiments indicate that chromatic stimulation is indexed by large N1 component and small offset responses. Optimal stimulus size for chromatic isolation is 2-4 ° along L/M axes and 6° along S/(L+M) axis. From the ERG experiments, It has been shown that the low (12Hz) and high (30Hz) temporal frequency flickering stimuli can isolate the chromatic and luminance processing mechanisms in the retina. For low temporal frequency ERGs, the L:M ratio was close to unity and L/M phase difference was close to 180°. For high temporal frequency ERGs, the L:M ratio was more than unity and L/M phase difference was close to 90°. In addition to this, the variation in L:M ratio across the retinal eccentricity was also examined. These results suggest, for the chromatic processing, L:M ratio is close to unity independent of retinal eccentricity and individuals. For the luminance processing, L:M ratio is more than unity and depends upon the region of the retina being stimulated. These findings indicate the maintenance of cone selective input for the chromatic processing across the human retina.

Techniques of colour measurement and colour reproduction are important in a wide range of commercial and social activities in most modern economies. Their study thus constitutes one of the major areas of interest to the CIE. The project described in this thesis began as an outgrowth of studies of new types of light sources and of the colorimetry of colour-TV systems; plus a conviction that modern TV cameras can operate effectively with a wide range of different illuminating spectra. It was soon evident that two important prerequisites for this research were: an understanding of the processes of human colour vision; and a knowledge of the standard, international, colorimetric terminology of the CIE. These topics are discussed fully in the text. Also included is a review of modern gas-discharge lamps, the~y properties, and their applications. Both high-pressure (HID) types and low-pressure (fluorescent-tube) types are considered. Because of the need to measure the colours of surfaces and their TV reproductions as accurately as possible, various forms of colorimeter were examined, leading to the choice of a spectrophotometer system for this work. The design, construction, and evaluation of an original spetrophotometer system (the UND Spectrophotometer) are described fully in the text. Finally, attention is given to the operation of a television system under nonstandard lighting. Twelve different light sources were evaluated as TV ((taking" illuminants, using both subjective and colorimetric methods of assessment. The experimental results tend to confirm that colorimetric methods are unsuited to colour reproduction evaluation, and that subjective methods are more meaningful. A subjective scale of colour reproduction performance was established, and it was found to correlate closely with the CIE general colour rendering index (Ra) for the various test lamps. The work reported herein predates similar experiments with TV lighting by other workers, and it includes a wider range of light sources. In spite of differences in experimental technique, however, there is broad agreement with their general results. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 1987.

The aim of this thesis is to defend what is known as the primary quality view of colour. It will do this by arguing that this view better meets our conceptual schema than either of its rivals the subjectivist view or the secondary quality view. In pursuing this project, I highlight the five core beliefs (as identified by Johnston 1992) that make up our colour conceptual schema, identifying the two strongly realist beliefs as making up our prime intuition, and on these grounds I immediately reject the subjectivist stance. I then set out the primary quality view's main rival, the secondary quality view, and show how dispositionalists have argued that this view is best able to accommodate our core beliefs. However, I identify empirical findings that raise problems for the secondary quality view, revealing its inability to satisfy our extended colour concepts as well as an inability to adequately explain certain deviant cases. The core of my argument against the secondary quality view comes from what I call problems of causation, where I argue that as dispositions are not causes they are unable to meet our prime intuition, and therefore cannot be colours. I therefore set up a version of the primary quality view of colour, identifying colours with microphysical properties (or complexes thereof) and show why this view does not face the same problems of causation as the secondary quality view. I then argue that the secondary quality view does not have the advantage over the primary quality view, when it comes to the rest of our core beliefs, as its supporters would have us believe. I show how a primary quality view is able to fit all these core beliefs into our overarching colour conceptual schema, without having to appeal to the ontological extravagances that dispositionists must bestow upon colour. Finally, I address two criticisms from commonsense that are laid against the primary quality view, and argue that the primary quality view is able to meet these conceptual demands and thereby conclude that the primary quality view is the better of the putative candidates competing for capturing the ontological status of colour. / Thesis (M.A.)-University of Natal, Pietermaritzburg, 2001.

Colour is an important source of information in the natural world. It can be used for distinguishing and identifying surfaces and objects and separating one region from another. For instance, flowers and grasses in a garden can be distinguished by their colours despite a change in illuminant. Intuitively, the identifiability of surfaces in a scene can be described by their volumes of colour gamuts. But is this approximation of the identifiability accurate? On the other hand, the existence of metamerism in natural scenes shows that colour is sometimes unreliable for surfaces identification. Estimating frequency of metamerism normally requires many comparisons between surface colours to determine their distinguishability under different illuminants. Is there a simpler approach to predict the frequency of metamerism in natural scenes? The aim of this thesis was to address these two questions about the identifiability of surfaces in natural scenes. To answer the first question, the volumes of colour gamuts were estimated over 50 natural scenes under different illuminants. The logarithm of the gamut volume was regressed on the differential entropy of colours. It was found that gamut volume can be an accurate approximation, given a colour difference threshold representing the visual distinguishability within an approximately perceptually uniform colour space. To answer the second question, the frequency of metamerism was estimated over 50 natural scenes with changes in illuminant; and predictive models were constructed based on different combinations of Shannon differential entropies of colours. There was strong dependence of the frequency of metamerism on the combination of the differential entropy and the conditional differential entropy of colours. It means that the frequency of metamerism can be predicted by the informational quantities of the colours in a scene.

The altitude at which oxygen supplementation should commence to be administered to aircrew in South Africa, flying in unpressurised aircraft is 12,000 feet. Above that altitude effects of reduced tissue oxygen content (hypoxia) become significant. Vision is particularly sensitive to hypoxia, and it was decided to test visual parameters at 12,000 feet to see if there were any subtle changes which might impair flight safety. It this were so, the level at which oxygen supplementation should commence would have to be lowered. The visual parameters to be assessed, all important in aviation, were colour vision, contrast sensitivity, and the presence of phorias (potential squints). 37 Healthy volunteers had these parameters assessed in an altitude chamber at ground level, 8,000 feet and 12,000 feet. Analysis of the results revealed no clinically significant degradation of vision at 12,000 feet, and it was concluded that the present altitude at which oxygen supplementation should begin (12,000 feet) is appropriate. It was advised that further testing should take place in subjects based at sea level. / Dissertation (MSc)--University of Pretoria, 2006. / School of Health Systems and Public Health (SHSPH) / Unrestricted

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