This dissertation investigates the processing of speech variability, allophonic and indexical variation in Japanese. A series of speech perception experiments were conducted with reduced and fully voiced vowels in Japanese as a test case. Reduced vowels should be difficult for listeners to hear because they are acoustically less salient than fully voiced vowels, due to the lack of relevant physiological properties. On the other hand, reduced vowels between voiceless consonants represent more common phonological patterns than fully voiced vowels. Furthermore, previous studies found that Japanese listeners were capable of hearing completely deleted vowels. Listeners intuitively maintain CV syllables in perception, hearing a vowel after each consonant in order to avoid obstruent clusters (a violation of Japanese phonotactics).It was found that listeners made good use of acoustic, phonological, and phonotactic knowledge of their native language for processing allophonic variants. In word recognition, listeners performed better when reduced vowels were in the environment where vowel reduction was expected. The phonological appropriateness of an allophone was judged in relation to adjacent consonants on both sides, and the facilitatory effect of appropriateness of reduced vowels surpassed the inhibitory effect of their acoustic weakness. However, in terms of sound detection, listeners found reduced and fully voiced vowels equally easy to hear in an environment where vowel reduction was expected. Although reduced vowels were phonologically appropriate between voiceless consonants, the phonological appropriateness merely balanced out acoustic weakness; it was not strong enough to surpass it. In addition, the phonological appropriateness of an allophone was judged based only on the preceding consonant, which suggests that listeners processed sounds linearly. Furthermore, the study found that phonological appropriateness of the allophone was affected by dialectal differences and speech rates. Listeners' preference for a certain allophone was influenced by the phonology of a listeners' native dialect and expectation was skewed by fast speech rates.This study suggests that current speech perception models need modification to account for the processing of speech variability taking language-specific phonological knowledge into consideration. The study demonstrated that it is important to investigate at which stage phonological inference takes place during processing.

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In speech perception tasks young infants show remarkable sensitivity to fine phonetic detail. Despite this impressive ability demonstrated at early ages, studies of word learning in young toddlers indicate that they have difficulty learning similar-sounding words. This evidence suggests that infants may not be using this speech-perception ability as they begin to learn words. The studies in this thesis were designed to test how infants' speech-perception skills are used in the early stages of word learning. Using a simple habituation procedure, we have shown in earlier work that 14-month-old infants, but not younger infants, are able to learn the association between novel nonsense words and objects (Werker, Cohen, Lloyd, Casasola, & Stager, 1998). The current series of experiments used this simple habituation procedure to test whether infants use minimally contrastive phonetic detail in the very early stages of word learning. In this thesis, I show that 14-month-old infants, who are on the cusp of word learning, while still able to discriminate phonetically-similar words in a speech perception task, do not incorporate minimally contrastive phonetic detail when first forming word-object associations. Infants of 8 months of age do, however, appear to use fine phonetic detail in a similar task. Taken together, these results suggest a decline in the phonetic detail used by infants as they move from processing speech to learning words. I hypothesize that this decline may occur as infants move from treating the task as one of speech perception to treating the task as one of word learning.

Previous research indicates that for adults and children the perception of speech can be significantly influenced by watching a speaker's mouth movements. For example, hearing the syllable /bi/ while watching a speaker mouth the syllable /vi/ results in reports of a 'heard' /vi/. Some evidence suggests young infants also may be able to integrate heard and seen speech. One theory suggests that an innate link between perception and production (Liberman & Mattingly, 1985) accounts for this phenomenon while another theory suggests that experience (e.g., producing speech sounds) may be necessary into order to develop fully the underlying representation of visible speech (Desjardins, Rogers & Werker, in press; Meltzoff & Kuhl, 1994). My dissertation addresses the above controversy by examining whether the integration of heard and seen speech is obligatory for young infants as it is for adults. In Experiment 1, 4-month-old female infants habituated to audiovisual /bi/ showed renewed visual interest to an auditory /bi/-visual NM suggesting that they may have perceived the auditory /bi/-visual /vi/ as /vi/, as do adults. In Experiment 2, neither male nor female infants showed renewed visual interest to a dishabituation stimulus which represents only a change in mouth movements. In Experiment 3, male infants looked longer to an audiovisual /bi/ than to an audiovisual /vi/ following habituation to an audio /bi/-visual /vi/, while female infants tended to look only slightly longer to an audiovisual /vi/ than to an audiovisual /bi/. Taken together these experiments suggest that at least some infants are able to integrate heard and seen speech, but that they do not do so consistently. Although an innate mechanism may be responsible for integration, a role for experience is suggested as integration does not appear to be obligatory for young infants as it is for adults.

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There is no abstract available for this thesis.

Seven monaural hearing aid users and four binaural hearing aid users (10 to 50 years old) were administered a hearing evaluation with earphones. Measures recorded were pure tone average (PTA), speech reception threshold (SRT), and speech discrimination scores. These results were compared with the results of an evaluation conducted one or more years previously. A t test was applied to the mean score differences from initial test to retest of the aided ears versus the unaided ears to determine the stability of speech discrimination in the unaided ear of persons with a bilateral loss of hearing sensitivity.PTA and SRT decreased minimally from initial test to retest indicating good threshold stability. Speech discrimination mean scores decreased, with a larger decrease observed for the unaided ears than the aided ears of monaural and binaural subjects. However, the larger decrease was not statistically significant. Therefore the data indicated that an ear which is not stimulated by amplification, with a hearing loss of sensitivity of 50dB HL to 80dB HL, does not have a significant decrease of speech discrimination as compared to an aided ear with a similar loss of hearing sensitivity.

Any phonological theory needs to encompass an account of acquisition and any account of acquisition must take its place within a general theory of phonology. This thesis aims to ascribe phonological significance to speech perception in infancy, a move impossible unless phonology is defined, as it is here, from both a psycholinguistic and a formal viewpoint as a dedicated pattern-recognition system. Extant results from infant studies are reviewed and aligned with current phonological theory. In particular, such theory characterises phonology as bi-modular, so the acquisition of individual melodic and prosodic modules and their subsequent orientation with respect to one another must constitute three different developmental tasks. This delivers a relatively simple account of the mapping between psychoacoustics and phonology. Perception and pre-existing theories of segmental complexity are related using an original experiment into the perception of vowel-height contrast in Catalan. If infant perception has phonological import, then disparate phonetic reflexes which are predicted as phonologically identical should show parallels in acquisition. General theory argues that the same abstract melodic objects underlie both laryngeal contrasts in stops and lexical tonal contrasts. Earlier studies show that language-specific attunement to stop contrasts has taken place by the age of six months. New tests are now reported, using children of the same age, which demonstrate that infants acquiring Yorùbá, a language which has a three-way contrast for tone, attend more closely to pitch changes within the minimal domain word than do English controls. Further, they only attend to those pitch changes that possess phonological import within that domain in the steady-state language. In this their perception exactly parallels that displayed by adult speakers. Apparent anomalies in the results of these tests are shown to be closely parallelled by phonological asymmetries in the tonology of Yorùbá.

Telephones are an integral part of everyday life in today's society. It is well known that hearing impaired people have difficulty understanding speech on the telephone. The ability to use the telephone is commonly reported as one of the many benefits of cochlear implantation. Assessment for a cochlear implant (CI) includes a variety of aspects related to communication and hearing ability. Included in the case history, mention is made whether the person can use the telephone. The purpose of the present study was firstly to identify if the inability to use the telephone could be used a predictor for suitability for a cochlear implant. It was also purposed to determine if telephone ability could be assessed by self-reported measures. The participants were 13 severe to profoundly hearing impaired people who had previously undergone candidacy assessment for a cochlear implant. Each participant was evaluated on their use and understanding of speech on the telephone. Participants were separated into two groups: those who were candidates for a cochlear implant and those who were not. Speech perception testing was evaluated using a recording of CUNY sentences on the telephone. Results indicated that cochlear implant candidates correctly perceived a significantly lower number of words on the telephone than non-candidates. Use of the telephone was evaluated using a 51-item questionnaire. Results indicated that there was no significant difference in self-reported use of the telephone between cochlear implant candidates and non-candidates. The differences in speech perception understanding on the telephone were most likely due to the overall better hearing levels of the non-candidates. The clinical implications of the present study are considered.

Thesis (M.S.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 38-41)