The annotated papers that are submitted as part of this thesis consider the phenomenon of colour at the fundamental, technical, and application levels, and they were written and published by Oulton between 1990 and 2009. The papers disclose significant insights by the author into colorimetric modeling theory and report aspects of the author's work that have led to commercially successful practical applications. The academic significance of these papers is evident in their citation record; their practical value is shown by a number of successful industrial collaboration programmes, and through the award of national prizes for innovation by the Worshipful Company of Dyers, and the Society of Dyers and Colorists. The published research primarily concerns digital devices that either capture or reproduce coloured images. For example, the research problem of how to calibrate the colour on computer CRT screens, which was thought at the time to be intractable, was reported by Oulton in paper 1 to be solved at the two to three significant figure level of colorimetric accuracy. This world leading level of accuracy was subsequently confirmed using a comprehensive data set in paper 7, and has been exploited internationally in commercial computer aided design and colour communication systems by Textile Computer Systems Ltd and Datacolor Inc. Further research problems resolved by Oulton in the presented papers include how to predict the colorimetric sensitivity of dye recipes; how to design, test, and fine-tune the spectral response of digital cameras; and how the individual customers in a shop can be tracked automatically to reveal their buying behavior, using coloured CCTV images.The challenge to the standard CIE colorimetric model posed by the results of Dr W.A. Thornton was analyzed and satisfactorily explained by Oulton in papers 2, 3 and 4. It is also shown that Thornton's results do not in any way compromise either the practice of colorimetry based on the CIE Standard Observer, or the validity of its quantifying data sets. It is also additionally shown under the annotation of paper 4 presented here, that the success of the CIE colorimetric model has a clearly demonstrable theoretical basis.In all but one of the presented papers the convention is maintained that the standard CIE XYZ co-ordinate model should be used as the reference basis, when modeling the properties of colour and quantifying its uses. The final paper to be published (and presented here as paper 4) challenges this convention and demonstrates that a context free and formally defined alternative reference basis may be used in colorimetric modeling with significant advantage. It is also shown in paper 4 that under the specified axioms, any cross dependency that is potentially non linear can in principle be resolved into its component scalar and additive relationships, and that the causes of scalar non linearity may be characterized independently from the causes of linearly additive cross dependency. The result is a widely applicable analytical and experimental design method for resolving complex cross dependent relationships in general and in particular, for resolving those between the spectral visual stimuli and the psychophysical response to them.

La désignation est le geste de montrer un objet à une autre personne. La structure de la désignation est similaire à celle du discours verbal : la première personne « je » communique avec la seconde personne « tu » à propos de l'objet « il ». A partir de la description neuropsychologique d'un trouble acquis de la désignation, l'hétérotopagnosie ou incapacité à désigner le corps d'autrui, nous jetons les bases d'un nouveau modèle de la désignation impliquant la notion de seconde personne « tu ». Nous proposons et validons l'hypothèse que toute désignation implique de se représenter le point de vue de l'interlocuteur « tu » grâce à un référentiel hétérocentré. De plus, chez les patients hétérotopagnosiques comme chez les volontaires sains, désigner le corps d'autrui est plus difficile que désigner les objets. Nous expliquons ce phénomène par le fait que seul le corps humain vivant peut être à la fois sujet de communication et objet de communication. Poursuivant notre investigation sur la notion de seconde personne, nous montrons chez une patiente et chez les sujets sains que le corps des femmes est également plus difficile à désigner que celui des hommes. Les femmes seraient plus facilement considérées comme des sujets que les hommes. Enfin, nous avons recherché comment l'humain percevait la désignation réalisée par autrui comme témoignant d'une intention de communication à propos d'un objet. L'engagement dans une relation avec la seconde personne « tu » est nécessaire à cette compréhension. Au total, cette thèse apporte les premiers éléments expérimentaux sur les mécanismes de la relation de communication avec la seconde personne « tu ». / Pointing is used to communicate about an object with another person. This skill has a triadic structure similar to speech: the first person “I” communicate with the second person “you” about an object of interest “it”. From the neuropsychological description of an acquired deficit in pointing, heterotopagnosia which is the inability to point at another person's body parts, we build a new cognitive model involving the notion of a second person to explain pointing behaviour. We bring experimental evidence that pointing requires taking the addressee's perspective through the elaboration of a heterocentric reference frame. Furthermore, we show that in heterotopagnosic patients and in healthy subjects pointing at another person's body is more difficult than pointing at objects. We hypothesize that it is because only the living human body of other can be a subject to communicate with and an object to communicate about. In addition, we show that heterotopagnosic patients and healthy subjects find it more difficult to point at female body parts than at male ones, perhaps because women are more easily considered as subjects. Finally, we explore the behavioural and neural bases of the perception of pointing. We confirm that the relationship with the second person is necessary to understand the communicative intention of the addressee about the object. As a whole, this work provides the first cognitive and neural evidence for the notion of a second person in the brain.

ABSTRACT Global summation of radial frequency patterns and the effect of sudden onset glare on shape discrimination The purpose of this study was to provide evidence of global pooling around the circumference of the Radial frequency (RF) pattern, and to study the effect of sudden onset glare on shape discrimination. The RF stimuli were generated by the amplitude modulation of the radius of a circle which deforms them from circularity, while the cross sectional luminance profile was the fourth derivative of Gaussians (D4). The amplitude of the stimuli determines how distinct the pattern is and thus measures the degree of sensitivity while the radial frequency determines the number of lobes the pattern has. In the first part of the study, whole RF patterns (RF3 to RF16) and open component fractions (0.125, 0.25, 0.5, 0.75), which are incomplete sectors of the whole, were tested against their respective reference unmodulated patterns. Subjects were tasked with discriminating minute deviations from their reference patterns. In the second part of the study, high contrast (20 X detection threshold) RF3 and RF4 contours and equivalent low contrast (5 X detection threshold) RF3 and RF4 contours were used as stimuli. Shape discrimination threshold for the high contrast target was determined with and without sudden onset glare. The result of the first part of the study showed that threshold decreased significantly as larger component RF patterns were tested (p < 0.05). The decrease could not be accounted for by the probabilistic sampling of local filters (probability summation). The result of the second part of the study showed that shape discrimination threshold increased with sudden onset glare. The increase was even more pronounced with lower mean luminance and when smaller fractions of the contours were tested. Shape discrimination threshold was significantly higher with high contrast contours in the presence of glare than equivalent low contrast contours, indicating that the veiling luminance model alone could not account for a decrease in visual performance in this shape discrimination task.

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This thesis documents a series of experiments designed to investigate the mechanisms subserving sub-second duration processing in humans. Firstly, duration aftereffects were generated by adapting to consistent duration information. If duration aftereffects represent encoding by neurons selective for both stimulus duration and non-temporal stimulus features, adapt-test changes in these features should prevent duration aftereffect generation. Stimulus characteristics were chosen which selectively target differing stages of the visual processing hierarchy. The duration aftereffect showed robust interocular transfer and could be generated using a stimulus whose duration was defined by stimuli invisible to monocular mechanisms, ruling out a pre-cortical locus. The aftereffects transferred across luminance-defined visual orientation and facial identity. Conversely, the duration encoding mechanism was selective for changes in the contrast-defined envelope size of a Gabor and showed broad spatial selectivity which scaled proportionally with adapting stimulus size. These findings are consistent with a second stage visual spatial mechanism that pools input across proportionally smaller, spatially abutting filters. A final series of experiments investigated the pattern of interaction between concurrently presented cross-modal durations. When duration discrepancies were small, multisensory judgements were biased towards the modality with higher precision. However, when duration discrepancies were large, perceived duration was compressed by both longer and shorter durations from the opposite modality, irrespective of unimodal temporal reliability. Taken together, these experiments provide support for a duration encoding mechanism that is tied to mid-level visual spatial processing. Following this localised encoding, supramodal mechanisms then dictate the combination of duration information across the senses.

La perception de la forme visuelle est le principal médiateur de la reconnaissance d’objets. S’il y a consensus sur le fait que la détection des contours et l’analyse de fréquences spatiales sont les fondements de la vision primaire, la hiérarchie visuelle et les étapes subséquentes du traitement de l’information impliquées dans la reconnaissance d’objets sont quant à elles encore méconnues. Les données empiriques disponibles et pertinentes concernant la nature des traits primitifs qu’utilise véritablement le système visuel humain sont rares et aucune ne semble être entièrement concluante. Dans le but de palier à ce manque de données empiriques, la présente étude vise la découverte des régions de l’image utilisées par des participants humains lors d’une tâche de reconnaissance d’objets. La technique des bulles a permis de révéler les zones diagnostiques permettant de discriminer entre les huit cibles de l’étude. Les zones ayant un effet facilitateur et celles ayant un effet inhibiteur sur les performances humaines et celles d’un observateur idéal furent identifiées. Les participants n’ont pas employé la totalité de l’information disponible dans l’image, mais seulement une infime partie, ce sont principalement les segments de contours présentant une discontinuité (i.e. convexités, concavités, intersections) qui furent sélectionnés par ces derniers afin de reconnaitre les cibles. L’identification des objets semble reposer sur des ensembles de caractéristiques distinctives de l’objet qui lui permettent d’être différencié des autres. Les informations les plus simples et utiles ont préséance et lorsqu’elles suffisent à mener à bien la tâche, le système visuel ne semble pas appliquer de traitement plus complexe, par exemple, l’encodage de caractéristiques plus complexes ou encore de conjonctions d’attributs simples. Cela appuie la notion voulant que le contexte influence la sélection des caractéristiques sous-tendant la reconnaissance d’objets et suggère que le type d’attributs varie en fonction de leur utilité dans un contexte donné. / The main mediator of visual object recognition is shape perception. While there is a consensus that contour detection and spatial frequency analysis are the foundations of early vision, the visual hierarchy and the nature of information processing in the subsequent stages involved in object recognition, remain widely unknown. Available and relevant empirical data concerning the nature of the primitive features used by the human visual system to recognize objects are scarce and none seems to be entirely conclusive. To overcome this lack of empirical data, this study aims to determine which regions of the images are used by humans when performing an object recognition task. The Bubbles technique has revealed the diagnostic areas used by 12 adults an ideal observer, to discriminate between eight target objects. stimulus areas with a facilitatory or inhibitory effect on performance were identified. Humans only used a small subset of the information available to recognize the targets which consisted mostly in discontinuous contour segments (i.e. convexities, concavities, intersections). Object recognition seems to rest upon contrasting sets of features which allow objects to be discriminated from one another. The simplest and most useful information seems to take precedence and it suffices to the task, the visual system does not engage in further processing involving for instance more complex features or the encoding of conjunctions of simple features. This implies that context influences the selection of features underlying human object recognition and suggests that attribute types can vary according to their utility in a given context.

This thesis presents a series of human psychophysical experiments designed to examine the interaction between the reliability of spatial form information and the neural mechanisms responsible for the processing of sub-second durations. Duration discrimination sensitivity was found to be lower when event durations were defined by stimulus characteristics that caused reductions in spatial form sensitivity. This form-duration sensitivity coupling persisted across stimuli defined both by crossed and uncrossed retinal disparity and within monocularly visible texture-defined stimuli. The interaction was also observed when spatial form was degraded by physical instability within shape borders, and when physically stable borders became perceptually unstable. These effects could not be attributed to artefacts of stimulus visibility, temporal coherence or stimulus size. Adaptation experiments generated aftereffects of perceived duration within stimuli whose durations were defined solely by retinal disparity, providing the first demonstration of duration selectivity within exclusively cortical duration encoding mechanisms. The selectivity of these aftereffects was then investigated using adapting and testing durations defined by matching or opposing retinal disparities. Duration aftereffects were maximal when adapt and test disparities were matched. However, there was partial transfer of duration aftereffects across large changes in retinal disparity, implicating contributions from higher-level extra-striate mechanisms. Collectively, these experiments provide support for duration processing mechanisms that are inextricably linked to the mechanisms underpinning spatial processing across multiple levels of the visuo-spatial hierarchy.

Glaucoma is the leading cause of irreversible blindness worldwide but the effect of glaucoma on patients’ vision under suprathreshold conditions relevant to their natural visual environment is poorly understood. This project aimed to investigate and further understand the effects of glaucoma on three aspects of suprathreshold vision; apparent contrast of suprathreshold stimuli, detection and discrimination of image blur and crowding of peripheral vision. Psychophysical methods were employed to assess these three visual functions by measuring contrast matches of Gabor stimuli, blur detection and discrimination thresholds of edge stimuli and crowding ratios of Vernier targets. These measures were obtained from glaucoma observers tested within and outside of visual field defects and the data compared with healthy controls. Contrast matching ratios were similar between glaucoma and healthy age similar controls despite sensitivity loss in the glaucoma group. Blur detection and discrimination thresholds were similar between glaucoma observers’ tested within and outside of visual field defects and age-similar controls, though thresholds were slightly elevated for high contrast stimuli in the glaucoma visual field defect group. Crowding ratios were similar between participants with glaucoma and healthy young controls. The results demonstrate that aspects of suprathreshold visual function can be maintained in early glaucoma despite sensitivity loss at threshold. The results provide empirical evidence as to the asymptomatic nature of the disease in its early stages. It appears that in early glaucoma, there may be compensatory mechanisms at work within the visual system under suprathreshold conditions that can overcome loss of sensitivity at threshold. / The College of Optometrists

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