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Observers can retrieve the facing direction of a walker from point-light displays that are devoid of structure-from-motion information and retain solely local motion signals. This ability is orientation-dependent and relies on the motions representing the feet of the agent. The experiments described here were designed to investigate visual sensitivity to local cues contained in biological motion. Initial experiments revealed that local biological motion carries information about animacy in addition to the agent’s facing direction in an orientation-dependent manner (Chapter 2). The mechanism underlying the perception of local biological motion can be dissociated from that underlying the retrieval of global structure-from-motion information according to characteristics such as sensitivity to learning and noise (Chapter 3). Further experiments revealed that the orientation-dependency for perceiving local biological motion is carried by vertical acceleration in the foot’s motion (Chapter 4). The importance of acceleration for biological motion perception raises the need to achieve a better understanding of acceleration sensitivity across various parameters such as stimulus size. To this end, Chapter 5 showed that acceleration thresholds for perceiving a linearly accelerating stimulus scale according to mean velocity as predicted by size invariance and are inversely proportional to stimulus duration. An important role for acceleration for the perception of biological motion was further corroborated by findings in an evolutionarily guided psychophysical search for the adequate local motion, defined as one that carries maximal directional information and a large inversion effect (Chapter 6). Finally, although orientation-dependency is a pervasively demonstrated characteristic of biological motion perception, the reference systems in which the stimuli are encoded are unclear. The experiments in Chapter 7 revealed that both global structure and local motion aspects of biological motion, like faces, are primarily coded in an egocentric frame of reference. Unlike faces however, there is an additional contribution of non-visual information about gravity for the perception of biological motion. These findings are finally discussed in the context of emerging behavioural, neuroimaging, and electrophysiological work that further characterize a local motion mechanism that is proposed to serve as a fundamental first stage towards interpreting animate motion patterns. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2010-07-21 08:34:58.564

Randomized clinical trials provide the best evidence on the effect of treatment studied. There are different types of measures on the treatment effect, depending on the endpoints of the trials. For a given measure, based on the data from clinical trials, various statistical procedures are available for the inference of the treatment effect in terms of this measure. In a cancer clinical trial with a time to an event as the endpoint, hazard ratio is a popular measure for the relative difference between treatment groups. Most current statistical inference procedures for hazard ratio rely on the proportional hazard assumption, which may not be applicable to practice when it does not hold. Nonparametric confidence intervals for the hazard ratio have been proposed based on the asymptotic normality of the kernel estimate for the hazard ratio, but they were found not very satisfactory in the simulation studies. In the first part of this thesis, the empirical likelihood method is used to construct the confidence interval for the time-dependent hazard ratio. The asymptotic distribution of the empirical likelihood ratio is derived and simulation studies are conducted to evaluate the proposed method. It was also argued that the measure of the relative treatment effect based on the hazard ratio may be difficult to understand by clinicians. An alternative measure called probabilistic index was suggested and the C-index was proposed to estimate this index. However, it was pointed out recently that the expected value of the estimate based on the C-index may be far removed from the true index. In the second part of this thesis, assuming a semi-parametric density ratio model, two new estimates based on respectively the conditional likelihood and weighted empirical likelihood are proposed. Associated confidence intervals are also derived based on the bootstrap re-sampling method. The proposed inference procedures are evaluated by Monte-Carlo simulations and applied to the analysis of data from a clinical trial on early breast cancer. After primary analysis including all patients is completed in clinical trials, analysis by subgroups defined based on covariates of patients is often of interest to assess the homogeneity of treatment effects over these subgroups. The treatment-covariate interaction is usually used for this assessment. In the last part of this thesis, a non-parametric measure is used to quantify the interaction between treatments and binary covariates in the presence of censoring. Asymptotic distribution of the interaction estimates are derived and the bootstrap method is applied to construct the confidence intervals. The proposed approaches are also evaluated and compared by Monte-Carlo simulations and applied to a real data set from clinical trial. / Thesis (Ph.D, Mathematics & Statistics) -- Queen's University, 2011-05-21 11:07:52.992

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The possible significance of cognitive and situational factors in determining the response to alcohol suggests that behavioral changes following drinking may reflect a lack of self-control not solely attributable to the pharmacological effect. In an initial experiment subjects were requested to overcome the effects of alcohol (1.32 ml/kg 95% ethanol). In comparison with a no-motivation group (n = 11), motivated subjects (n = 14) demonstrated compensation on aspects of tasks involving memory, coordination and affect. It was speculated that attributions of causality (internal or external) for relative control might influence its occurrence and maintenance. In a second experiment false dose feedback was expected to interact with relative control to affect subjects' (n = 45) attributions. A greater level of sobriety was achieved by subjects who were led to attribute responsibility to themselves. Also, it appeared that further drinking was affected by cognitive influences. Implications of the self-control phenomenon, especially regarding the non-pharmacological role and the etiology of excessive drinking, are discussed.

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