This dissertation studies the perception of tones in Thai, and aims to contribute to a formal characterization of speech perception more generally. Earlier work had argued that perception of tones involves retrieval of some abstract "autosegmental" representation provided by the phonology, while another line of work had argued for the retrieval of f0 trajectory information, which one may regard as a phonetic representation. In contrast to this dichotomy, experimental studies in the segmental domain had shown that perception is equally attuned to both phonological and phonetic properties. Based on this, the dissertation argues for a formal architecture in which both phonological and phonetic constraints are available to perception, hence enabling perception to match acoustic inputs not only to phonological but also to phonetic representations as well. In the domain of tone, this predicts that perceptual tasks such as categorization should be aided not only by acoustic information that may relate to the "autosegmental" (phonological) representation of tones, such as High or Low pitch targets and their position within the syllable, but also by the details of the f0 trajectory, which one may regard as phonetic. The dissertation then presents two experiments involving perception of Thai tones, which are argued to show that, indeed, not only targets, but trajectories play a role, since manipulation of trajectories prove to affect perception. These results are confirmed by statistical modeling of the experimental results. It is shown that a relatively more successful model is one that employs a hybrid measure in comparing an incoming stimulus to a mental category, a measure consisting of a weighted combination of both target-based and trajectory-based distances. Finally, it is shown that the successful statistical model can receive a straightforward implementation in Harmonic Grammar, an appropriate tool for linguistic analysis in general, and well suited to the overall formal architecture being proposed in this work. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]