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. 2021 Jul 14;11(3):357-364.
doi: 10.3390/audiolres11030033.

Word Categorization of Vowel Durational Changes in Speech-Modulated Bone-Conducted Ultrasound

Tadao Okayasu  1 , Tadashi Nishimura  1 , Akinori Yamashita  1 , Yoshiki Nagatani  2 , Takashi Inoue  3 , Yuka Uratani  1 , Toshiaki Yamanaka  1 , Hiroshi Hosoi  4 , Tadashi Kitahara  1
Affiliations

Word Categorization of Vowel Durational Changes in Speech-Modulated Bone-Conducted Ultrasound

Tadao Okayasu et al. Audiol Res. .

Abstract

Ultrasound can deliver speech information when it is amplitude-modulated with speech and presented via bone conduction. This speech-modulated bone-conducted ultrasound (SM-BCU) can also transmit prosodic information. However, there is insufficient research on the recognition of vowel duration in SM-BCU. The aim of this study was to investigate the categorization of vowel durational changes in SM-BCU using a behavioral test. Eight Japanese-speaking participants with normal hearing participated in a forced-choice behavioral task to discriminate between "hato" (pigeon) and "haato" (heart). Speech signal stimuli were presented in seven duration grades from 220 ms to 340 ms. The threshold at which 50% of responses were "haato" was calculated and compared for air-conducted audible sound (ACAS) and SM-BCU. The boundary width was also evaluated. Although the SM-BCU threshold (mean: 274.6 ms) was significantly longer than the ACAS threshold (mean: 269.6 ms), there were no differences in boundary width. These results suggest that SM-BCU can deliver prosodic information about vowel duration with a similar difference limen to that of ACAS in normal hearing.

Keywords: amplitude modulation; bone-conduction; prosody; ultrasonic perception; ultrasound; vowel.

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Conflict of interest statement

All authors declare no conflict of interest related to this manuscript.

Figures

Figure 1
Figure 1
Speech signal waveforms of the original speech and the speech-modulated ultrasonic sounds.
Figure 2
Figure 2
Evaluation of the categorization boundary using a logistic function.
Figure 3
Figure 3
Logistic functions for air-conducted audible sound (ACAS) (a) and speech-modulated bone-conducted ultrasound (SM-BCU) (b).
Figure 4
Figure 4
Threshold (a) and boundary width (b) for ACAS and SM-BCU. The asterisk indicates a statistically significant result from the Wilcoxon matched-pairs signed rank test (* p < 0.05). ACAS, air-conducted audible sound; SM-BCU, speech-modulated bone-conducted ultrasound.
Figure 5
Figure 5
Envelope of 280 ms speech signal for ACAS and SM-BCU. ACAS, air-conducted audible sound; SM-BCU, speech-modulated bone-conducted ultrasound; TFS, temporal fine structure.
See this image and copyright information in PMC

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