| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1998: ¥200,000 (Direct Cost: ¥200,000)
Fiscal Year 1997: ¥200,000 (Direct Cost: ¥200,000)
Fiscal Year 1996: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
Sound stimuli are transformed into two kinds of information in the cochlea : frequency information and temporal information, which has been shown to play a important role in speech perception. We investigated temporal patterns of compound action potentials (CAPs) recorded with electrocochleography (EcochG), a good indicator of temporal speech coding in the human cochlea. There were following characteristic responses of CAPs evoked by single vowel [a] voiceless consonant [ka] and the voicedconsonant syllables [ma], [ba], and [da] were investigated. 1) Periodic CAPs with the same intervals as the pitch periods through the vowel parts of all stimuli (This interval reflects the period of the fundamental frequency of voice) 2) Absence of or low-amplitude CAPs at the onset of each voiced consonant 3) CAPs synchronized with the voiced part (buzz) of [in] 4)Prominent CAPs at the bursts of the stop consonants [k], [b] and [d]. These differences between temporal information of speech sound contr
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ibute to speech perception.
We developed a compression-amplification in the time-domain method (TD-1 method) of sound pressure levels during each variable time phase in order to input temporal information of speech sound to the cochlea more effectively. We observed the temporal information of speech sound coded at the cochlea using the CAPs as an indicator in 12 patients with sensory hearing loss (SHL) in order to prove the effectivity of TD-1 method to code the temporal information of speech sound at the cochlea in SHL.CAPs evoked by [ka] revealed abnormal patterns in all patients, but when the sound stimuli [ka] was processed by the TD-1 method, the CAP at the onset of, [k], was recognized in 7 patients, therefore in total, 8 out of 12 patients showed the normal CAP patterns at the onset. In one patient, the delayed onset of CAPs of the vowel part was improved, and in 4 patients, both CAPs at the onset and of the vowel part were normalized. These results suggest that the temporal information of speech sound, especially that of consonant, can be effectively coded when processed by the TD-1 method. Less
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