The experiments described in this thesis investigate the temporal relationship between frequency bands in a cochlear implant sound processor. Initial studies were of cochlea-based traveling wave delays for cochlear implant sound processing strategies. These were later broadened into studies of an ensemble of across-frequency delays. / Before incorporating cochlear delays into a cochlear implant processor, a set of suitable delays was determined with a psychoacoustic calibration to pitch perception, since normal cochlear delays are a function of frequency. The first experiment assessed the perception of pitch evoked by electrical stimuli from cochlear implant electrodes. Six cochlear implant users with acoustic hearing in their non-implanted ears were recruited for this, since they were able to compare electric stimuli to acoustic tones. Traveling wave delays were then computed for each subject using the frequencies matched to their electrodes. These were similar across subjects, ranging over 0-6 milliseconds along the electrode array. / The next experiment applied the calibrated delays to the ACE strategy filter outputs before maxima selection. The effects upon speech perception in noise were assessed with cochlear implant users, and a small but significant improvement was observed. A subsequent sensitivity analysis indicated that accurate calibration of the delays might not be necessary after all; instead, a range of across-frequency delays might be similarly beneficial. / A computational investigation was performed next, where a corpus of recorded speech was passed through the ACE cochlear implant sound processing strategy in order to determine how across-frequency delays altered the patterns of stimulation. A range of delay vectors were used in combination with a number of processing parameter sets and noise levels. The results showed that additional stimuli from broadband sounds (such as the glottal pulses of vowels) are selected when frequency bands are desynchronized with across-frequency delays. Background noise contains fewer dominant impulses than a single talker and so is not enhanced in this way. / In the following experiment, speech perception with an ensemble of across-frequency delays was assessed with eight cochlear implant users. Reverse cochlear delays (high frequency delays) were equivalent to conventional cochlear delays. Benefit was diminished for larger delays. Speech recognition scores were at baseline with random delay assignments. An information transmission analysis of speech in quiet indicated that the discrimination of voiced cues was most improved with across-frequency delays. For some subjects, this was seen as improved vowel discrimination based on formant locations and improved transmission of the place of articulation of consonants. / A final study indicated that benefits to speech perception with across-frequency delays are diminished when the number of maxima selected per frame is increased above 8-out-of-22 frequency bands.

Thesis (M.S.)--Missouri State University, 2009. / "May 2009." Includes bibliographical references (leaves 29-30). Also available online.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / PURPOSE: to propose a version of the Portuguese Sentences Lists test with slowed speech speed; to verify the naturalness, clarity and applicability of the new material; to evaluate the change in the recognition performance in adults and elderly with the variation of the speech s speed; to verify hearing loss and speed of the verbal stimulus presentation variables on the speech recognition in the elderly. METHODS: was realized elongation of 25% compared to the original duration of the Portuguese Sentences Lists test. Adults and elderly normalhearing did a perceptual analysis of the produced material. After this, the adults had obtained their Slowed Sentences Recognition Thresholds in Quiet, Slowed Sentences Recognition Indices in Quiet and Sentences Recognition Indices in Quiet. The data were subjected to statistical analysis. Both normal-hearing elderly, than elderly people with hearing loss were subjected to these same evaluations, and have also been submitted to obtain their Sentences Recognition Indices in Noise, Slowed Sentences Recognition Indices in Noise. The data were statistically analyzed and compared. RESULTS: the modified material was recorded on Compact Disc. After its presentation to adults and elderly normal-hearing, which performed the perceptual analysis of the test, it was considered clear and natural. The evaluations, through the Portuguese Sentences Lists and Portuguese Slowed Sentences Lists tests, showed that an improvement was observed with the presentation of the slowed stimuli in relation to the presentation at typical speed in the group of adults to the measurements obtained in silence, but without statistical significance. As for as the groups of elderly normal-hearing and older people with hearing loss, was also observed an improvement in slowed sentences recognition, but with a statistically significant difference. Regarding the noise assessments carried out with the elderly, was obtained statistically significant improvement in the presentation of the sentences at a slowed speed in the group with hearing loss, but not in the elderly normal-hearing one. CONCLUSION: the modified material, named Portuguese Slowed Sentences Lists test, proved applicability and sensibility to investigate the temporal aspects influence in speech recognition in the older people. The elderly demonstrated more ease to understand the spoken message, when it was presented with slowed speed. The findings of this research shows that the elderly, independent of the peripheral hearing, have best benefit on the speech recognition, when the heard message is slower in the silence. Considering the speech in noise, have been shown evidence that older adults with hearing loss had more benefit when the speech is slowed than those with normal hearing. / OBJETIVOS: propor uma versão do teste Listas de Sentenças em Português com menor velocidade de fala; verificar a naturalidade, clareza e aplicabilidade do novo material desenvolvido; aplicar ambos os testes em sujeitos adultos e idosos e avaliar a mudança no desempenho de reconhecimento da fala destes com a variação da velocidade de apresentação do estímulo verbal; verificar as variáveis perda auditiva e velocidade de apresentação do estímulo verbal no reconhecimento de fala em idosos. MATERIAL E MÉTODO: neste estudo, foi realizada elongação de 25% em relação à duração original das frases do teste Listas de Sentenças em Português. Adultos e idosos normo-ouvintes fizeram uma análise perceptivo-auditiva do material produzido. Após, o grupo de adultos teve seus Limiares de Reconhecimento de Sentenças Lentificadas no Silêncio, Índices Percentuais de Reconhecimento de Sentenças Lentificadas no Silêncio e Índices Percentuais de Reconhecimento de Sentenças no Silêncio obtidos. Tanto idosos normo-ouvintes, quanto idosos com perda auditiva foram submetidos a estas mesmas avaliações, além de terem sido submetidos também à obtenção dos Limiares de Reconhecimento de Sentenças Lentificadas no Ruído, Índices Percentuais de Reconhecimento de Sentenças Lentificadas no Ruído e Índices Percentuais de Reconhecimento de Sentenças no Ruído. Os dados obtidos foram submetidos à análise estatística e comparados. RESULTADOS: o material modificado foi gravado em Compact Disc. Após sua apresentação a indivíduos adultos e idosos normo-ouvintes, que realizaram análise perceptivo-auditiva do teste, este foi considerado claro e natural. As avaliações realizadas, através dos testes Listas de Sentenças em Português e Listas de Sentenças Lentificadas em Português, demonstraram que foi verificada melhora de desempenho com a apresentação dos estímulos em velocidade diminuída, em relação à apresentação em velocidade típica no grupo de adultos para as medidas obtidas no silêncio, porém sem significância estatística. Já para os grupos de idosos normo-ouvintes e de idosos com perda auditiva, também verificou-se melhora com o reconhecimento de sentenças em velocidade diminuída, porém com diferença estatisticamente significante. Em relação às avaliações no Ruído, realizadas com os idosos, obteve-se melhora estatisticamente significante à apresentação das sentenças em velocidade diminuída no grupo com perda auditiva, mas não no de idosos normo-ouvintes. CONCLUSÕES: o material modificado, nomeado Listas de Sentenças Lentificadas em Português, mostrou-se aplicável e sensível para investigar a influência de aspectos temporais no reconhecimento da fala em idosos. Os achados da presente pesquisa evidenciam que os idosos, independente da audição periférica, se beneficiam no que concerne ao reconhecimento da mensagem ouvida, quando a fala é realizada em velocidade mais lenta no silêncio. Quanto à fala no ruído, foram mostrados indícios de que idosos com perda auditiva se beneficiaram mais do que aqueles com normalidade auditiva, quando a velocidade da fala é diminuída.