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聴覚フィードバックにおける骨導音声の伝達過程に関する研究

Author(s)鳥谷, 輝樹CitationIssue Date

2021‑03

TypeThesis or Dissertation

Text version

ETDURLhttp://hdl.handle.net/10119/17479

RightsDescription

Supervisor:鵜木祐史, 先端科学技術研究科, 博士

Japan Advanced Institute of Science and Technology

Abstract
During speaking, humans perceive their own voices to control their speech production systems. This mechanism is reﬀered to as auditory feedback. Previous psychological and neurological studies related to auditory
feedback have suggested the importance of acoustical monitoring during speech production. Those studies havemainly focused only on air-conducted (AC) speech transmission of one’s own voice. However, there is anothertype of speech transmission: bone-conducted (BC) speech. It is still unclear whether/how BC speech perception during speaking aﬀects one’s speech production as auditory feedback, as well as AC speech. Althoughsome studies have used acoustical stimuli such as a pink noise for masking one’s BC speech, it has not beenclariﬁed whether the noise stimuli successfully mask one’s BC speech enough or not. For further exploring theauditory information during speaking, the following things need to be understood: (1) acoustical characteristics
of BC speech, (2) transmission pathways and transmission characteristics, (3) perceptual contribution of eachtransmission pathway.
Physiological studies related to BC hearing have argued that the glottal vibration and the sound inside
the vocal tract are transmitted to the auditory system (i.e., the outer, middle and inner ear) as BC speechthrough multiple pathways. Since BC speech transmission to the middle and the inner ear cannot be observeddirectly, previous studies have not obtained consistent ﬁndings regarding the contribution of the middle/inner
ear pathways to BC speech perception.
This study aims to clarify the process of the BC speech transmission from the vocal organ to the auditory
system from the above aspects ((1) to (3)), hypothesizing that the spectral characteristics of the BC speechcomponent reacing the middle/inner ear correspond to those of the vibration of regio temporalis (RT).
Firstly, the fundamental frequency (F0) and the spectral characteristics of BC speech were analyzed focusingon the RE vibration and the sound radiation in the ear canal (EC) during speaking. It was found that the RT
vibration included the same information of the fundamental frequency (F0) and the lower-order formants below
2 kHz as AC speech, while the EC sound radiation includes the same information of F0, the ﬁrst formant (F1)and the second formant (F2) as AC speech.
Secondly, transmission characteristics from the vocal organ to the RT and the EC were measured usingtranscutaneous excitation on the larynx and excitation from a sound source in the oral cavity. The measurementfound that BC transmission from the vocal organ to the outer ear has an eﬀect of band-pass ﬁltering between 1
to 3 kHz, while BC transmission from the vocal organ to the middle/inner ear has an eﬀect of low-pass ﬁltering
below 2 kHz.
Thirdly, voice timbre of one’s own voice were subjectively evaluated using the transmission characteristics
obtained above, to investigate perceptual contribution of AC and BC speech transmission. The evaluation foundthat the middle-/inner-ear part of transmission contributes BC speech perception almost as the same extent asthe outer-ear part of transmission.
From the three ﬁndings above, this research indicated that not only the outer-ear but also the middle/innerear part of BC speech transmission may play a role mainly in monitoring the pitch information as auditory
feedback. The transmission characteristics obtained in this study is helpful in designing the masking stimuli
for the auditory feedback experiment. The role of BC speech perception in auditory feedback is expected to berevealed in future studies.
Keywords: Auditory feedback, bone-conducted speech, transmission characteristics, vocal organ,
auditory system