Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 126-134). Available also in a digital version from Dissertation Abstracts.

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Thesis (Ph.D.)--University of Texas at Dallas, 2008. / Includes vita. Includes bibliographical references (leaves 89-92)

Thesis (Ph. D.)--University of Hong Kong, 1991.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 116-134). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph.D.)--Boston University. / Rats were trained on three schedules of reinforcement, a sound aversive schedule, a light aversive schedule and a sound and light discrimination schedule. On the aversive schedules a press response terminated the aversive stimulus. On the discrimination schedule a response in the presence of either stimulus produced food. An auditory threshold was measured on this schedule. Following training the animals received electrolytic lesions in the ventral auditory system of the medulla. Following this they were tested on the behavioral schedules. The brain of each animal was then removed and impregnated with protargol for microscopic examination. Six rats received unilateral lesions, seven received bilateral lesions and six received sham operations. The results were as follows. Of the six animals who received unilateral lesions, one showed a substantial loss of the sound aversive behavior. Of the seven who received bilateral lesions five suffered a loss of the aversive behavior. Of these five, two had a substantial increase in the discriminative threshold. The behavior of the animals who received sham operations was essentially unaffected. There was a consistent relation between extensive damage to the large fiber pathway, the superior olivary pathway and the small fiber pathway and loss of the auditory aversive behavior. Destruction of the superior olivary pathway was not sufficient to produce a loss of the aversive behavior. The suggestion in the literature that the large fiber pathway is responsible for the maintenance of the aversive behavior was confirmed. Destruction of the superior olivary pathway either alone or in combination with destruction of the large fiber pathway did not materially change the auditory discriminative threshold. Destruction of all ventral acoustic pathways caused a loss of both aversive and discriminative auditory behaviors. Dorsal auditory pathways did not by themselves support either behavior. It has not been possible to determine if destruction of the small fiber pathway by itself can cause a loss of discriminative behavior. It was not possible to determine if return of the release response was due to the lesion or due to the loss of the press response.

A listener's sensitivity to the presence of a sinusoidal target, masked by a sample of random noise, is known to depend on the specific noise sample for both monaural and binaural detection [Gilkey, Robinson, and Hanna, J. Acoust. Soc. Am. 78:1207-1219, 1985]. This work explores to what extent existing quantitative models for binaural detection can predict the sample-by-sample variation observed in listeners' responses. Responses of five subjects for the binaural detection of a 500-Hz, 300-msec, interaurally out-of-phase tone masked by statistically independent samples of narrowband, interaurally-identical noise are reported. A set of 30 noise samples were taken from a noise process with a power spectrum that is 115-Hz wide, centered at 500 Hz. The rms noise pressure is 75 dB SPL. For each subject, the responses show good self-consistency and a strong dependence on individual noise samples (intrasubject correlation coefficients higher than 0.72, typically 0.85). However, there are significant differences between subjects in the pattern of responses across the set of masker samples (intersubject correlation coefficients no higher than 0.7). Subjects' performance values for individual noise samples are compared to the predictions of psychophysical models for binaural detection. Some classes of previously suggested models have predictions that are not consistent with observed performance. Specifically, sample-level predictions of models for which the decision variable is dominated by the energy in the particular noise sample have no significant correlation with the patterns of responses across noise samples for any subject. In contrast, models that are based on variability of the ITD and/ or IID have predictions that are statistically significantly correlated with most subjects' responses (but no correlation coefficients larger than 0. 7). Black-box models in this class include those with decisions based on the sum of the squares of the ITDs and IIDs, or on the peak-deviations of the ITDs. Results for a physiological model of the dependence of firing patterns of the principal cells in the medial superior olive on ITDs suggest a mechanism that is analogous to black-box models with decision variables based on the variability of the ITD.

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

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