This master’s thesis deals with muscles physiology of eye movement and questions of surface electromyography measurement. Physiology and analysis of eye movement are described here. Furthermore the paper deals with a variety of electrooculographic measuring techniques and also with resulting evaluation of measured signal.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Yes / Purpose There is a high level of over-referral from primary eye care leading to significant numbers of people without ocular pathology (false positives) being referred to secondary eye care. The present study used a psychometric instrument to determine whether there is a psychological burden on patients due to referral to secondary eye care, and used Rasch analysis to convert the data from an ordinal to an interval scale. Design Cross sectional study. Participants and Controls 322 participants and 80 control participants. Methods State (i.e. current) and trait (i.e. propensity to) anxiety were measured in a group of patients referred to a hospital eye department in the UK and in a control group who have had a sight test but were not referred. Response category analysis plus infit and outfit Rasch statistics and person separation indices were used to determine the usefulness of individual items and the response categories. Principal components analysis was used to determine dimensionality. Main Outcome Measure Levels of state and trait anxiety measured using the State-Trait Anxiety Inventory. Results State anxiety scores were significantly higher in the patients referred to secondary eye care than the controls (p<0.04), but similar for trait anxiety (p>0.1). Rasch analysis highlighted that the questionnaire results needed to be split into “anxiety-absent” and “anxiety-present” items for both state and trait anxiety, but both subscales showed the same profile of results between patients and controls. Conclusions State anxiety was shown to be higher in patients referred to secondary eye care than the controls, and at similar levels to people with moderate to high perceived susceptibility to breast cancer. This suggests that referral from primary to secondary eye care can result in a significant psychological burden on some patients. / University of Bradford

La recherche présentée dans cette thèse est divisée en trois parties. Notre objectif dans la première partie est l’amélioration de la compression de l’image par stéganographie. Dans cette étude, la compression de données est effectuée en deux étapes. Tout d’abord, nous profitons du compactage d’énergie en utilisant JPEG pour réduire les données redondantes. Ensuite, nous intégrons des blocs de bits dans les blocs suivants de la même image stéganographie. Les bits intégrés servent à non seulement augmenter la taille du fichier de l’image compressée, mais aussi à diminuer davantage la taille du fichier. Les résultats expérimentaux montrent que notre méthode donne de meilleurs taux de compression tout en conservant une haute qualité de l’image. Le deuxième sujet de cette thèse propose un formalisme bayésien pour la stéganalyse d’image numérique qui permet la détection d’images stego, l’identification de l’algorithme de stéganographie utilisé, l’estimation de la longueur du message et l’emplacement, et l’anticipation dans le cas de l’intégration en utilisant un algorithme de stéganographie inconnu. La détection, l’identification et l’anticipation impliquent l’apprentissage discriminant dans l’espace des fonctions. L’estimation nécessite la fusion de classificateurs permettant la discrimination entre les sous-images et une intégration entière des couvertures de tailles différentes. La validation sur des images JPEG montre que le système proposé est efficace et permet d’anticiper des algorithmes de stéganographie inconnus. Le troisième sujet de la thèse décrit une méthode d’estimation du regard de l’oeil humain pendant un mouvement normal de la tête. Dans ce procédé, la position et l’orientation de la tête sont acquises par des données de profondeur fournies par Kinect. La direction de l’oeil est obtenue à partir d’images à haute résolution. Nous nous proposons la régression logistique multinomiale pour construire une fonction de mappage du regard et de vérifier l’état de l’iris. L’efficacité de la méthode proposée est validée par une évaluation de la performance pour plusieurs personnes avec différentes distances et poses par rapport à la caméra et dans différents états de l’oeil.

Precognition can be defined as an anomalous correlation between current cognitive activity and a future event. Using behavioural and physiological measures, a number of previous studies have reported evidence for unconscious precognition during a variety of task conditions. The current thesis presents five experiments that were designed to test for unconscious precognition in the visual attention system while participants were engaged in a short term visual memory task. Each trial consisted of a study and test phase. In the study phase, participants were required to memorise an array of four stimuli while their eye movements were recorded. After a brief retention interval, a probe stimulus was presented for a yes/no recognition test. Two conditions were employed and were randomly determined. In the old condition, the probe was a stimulus viewed during study, termed the target. In the new condition, the probe was a novel stimulus. Experiments tested for the presence of precognition by examining whether there was a difference in the degree to which visual attention was allocated to items during the study phase of old and new trials. Two further studies were also carried out involving simulations that aimed to establish the extent to which a previously described artefact, termed the expectation bias, may impact on the results. Experiment 1 suggested that participants spent more time attending to target stimuli in old compared to new trials, a result that appeared to provide evidence for precognition. However, the data was considered unreliable due to inadequate randomisation. An exact replication of Experiment 1 was carried out in Experiment 2 with adequate randomisation, but failed to find evidence for precognition. Experiment 3A was a further attempt to replicate the preliminary results of Experiment 1 using more extensive randomisation procedures while Experiment 3B explored the potential role of the probe stimulus in generating a precognitive effect. However, no support for the precognitive hypothesis was found in either experiment. A fully balanced design was employed in Experiment 4 in order to control for potential confounds such as position and saliency effects. The results supported the precognitive hypothesis and suggested that less attention was allocated to targets in the old condition. An exploratory analysis also examined the relationship between several standardised stimulus variables and the apparent precognitive effect observed in Experiment 4. The results revealed a suggestive relationship between the size of the effect and item ratings of familiarity and visual complexity. Simulations of an expectation bias in Experiments 5A and 5B together with post-hoc examination of the data from the current series of experiments suggest that this artefact is not a plausible explanation for the observed effects. The thesis ends with a discussion of several methodological issues that may impact on both the interpretation of positive results and the conclusions that may be reached from this body of data as a whole. Finally, suggestions for further work are made.

Many studies have found evidence of abnormal eye movement control in Parkinson's disease. Deficits in the inhibition of unintended saccades and slowed initiation of intentional saccades have been reported in some, but not all, investigations. Also over recent years the presence of cognitive impairment in a proportion of patients with Parkinson's disease has been highlighted. Efficient use of working memory resources is thought to be involved in the performance of tasks in both domains. With a comprehensive selection of saccadic and neuropsychological tasks, the current study investigated whether aspects of abnormal oculomotor control are associated with impairment of cognitive functions. Nineteen Parkinson's disease patients and eighteen healthy age matched control subjects performed six eye movement tasks and completed a neuropsychological test battery assessing five different aspects of cognitive functioning. Deficits were found in both the oculomotor and the cognitive domain in the group of patients. As a group, the patients made more reflexive errors in antisaccade tasks, more inhibition errors in a delayed response task, and were slower to initiate intentional saccades. The three measures of abnormal oculomotor control were not consistently associated with cognitive impairments or with each other. Longer latencies of correct antisaccades and increased number of errors in a delayed response task were associated with lower scores in different cognitive tests. Reflexive errors in the antisaccade task were not associated with cognitive deficits, but with the tendency to produce very fast visually triggered responses. The results suggest that, at least in Parkinson's disease, different neural mechanisms may be involved in specific aspects of abnormal oculomotor control.

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