The occurrence of spikes during an electroencephalogram is a basic feature of Benign Epilepsy of Childhood (BREC). In this thesis we analyze several problems related to the structure of such spikes. The currently used mathematical model describing the spike assumes that all the inter-spike variations are due to background activity. We show that non-negligible additional variability is present during the spike and propose a slightly richer model which takes such variability into account. In particular we conclude that background noise may not be used to assess the precision of the estimates of the signal. The technique of spike averaging is presently used to obtain more precise estimates of the signal. By comparing averaging with trimmed mean, median and the "lowess" smoother, we find no discrepancies indicating the presence of skewness or long tails in the underlying distribution of the data and conclude that spike averaging is an adequate method for estimating the deterministic part of the spike. Next, three automated procedures for the detection of the peak of the spike are compared to the existing method, which is based on a visual analysis of the EEG tracing. None of the alternative methods is found to be superior, but the methodology developed for this problem is rather general and could be applied to other similar comparisons. Finally we address the question of whether "atypical" BREC patients, who are characterized by having other neurological abnormalities besides seizures, have a spike structure different from that of the "typical" patients. The non parametric method of "classification trees" is discussed and then applied to find whether certain features of the spike can discriminate between typical and atypical patients. The location and amplitude of the spike are found to provide a satisfactory classification rule, suggesting that the two groups may be affected by different types of epilepsy. We have used, throughout the thesis, simple methods which do not require strong assumptions. In particular we have tried to avoid assumptions of normality and linearity and to rely mostly on non parametric methods. / Science, Faculty of / Statistics, Department of / Graduate

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Speech perception is a unique audiovisual experience in part because timing of the speech signal is influenced by simultaneous overlapping gestures in coarticulation. Apraxia of speech (AOS) is a motor planning disorder that impairs coarticulation. Imaging studies show that brain regions damaged in AOS are critical to audiovisual speech perception. Although AOS is a motor planning disorder, individuals with AOS may have a disruption to the perceptual system for speech gestures. To evaluate this hypothesis we investigated audiovisual mismatch negativity (MMN) brain responses in adults with damage to Broca’s area (n =5) compared to a healthy age-matched comparison group (n = 5). We utilized the McGurk effect, in which incongruent auditory and visual information alters perception. Participants viewed videos of a speaker articulating the syllable /ba/ (standard) for 80% trials and /ga/ (deviant) for 20% of the trials while the auditory stimulus /ba/ remained consistent throughout. Responses to this McGurk audiovisual condition were compared to an inverse McGurk audiovisual condition in which the visual stimulus remained constant while the auditory stimulus changed, and a visual-only condition without sound to control for evoked activity from changes to the visual stimulus. Incongruent McGurk deviants elicited an MMN over left hemisphere electrodes in the comparison group, while the AOS group exhibited a later, attention-based response, a P300. The AOS group similarly responded to inverse McGurk deviants, which do not require fusion of the percept, with a P300 response, indicating that auditory and visual aspects of the incongruent McGurk deviants were not integrated. In the visual-only control condition, the AOS group showed a left-lateralized MMN, suggesting greater influence of visual processing when confronted with conflicting multisensory information compared to the comparison group. Overall, the comparison group’s responses were indicative of early and automatic audiovisual integration of incongruent McGurk percepts while the responses of the AOS group showed contributions of both attentional and visual processing. The timing of the response in the AOS group was correlated with speech production characteristics of apraxia, as well as performance on taxing motor speech tasks. Results of this study support the hypothesis that AOS is a disorder beyond motor planning, with implications for higher-level linguistic and cognitive systems.

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B.G. Farley ... [et al.]. / "6 November 1957." / Bibliography: p. 19. / Army Signal Corps Contract No. DA36-039-sc-64637 Dept. of the Army Task 3-99-06-108 Project 3-99-00-100 Air Force Contract No. AF 19(122)-458