The Japanese unrounded back vowel /ɯ/ is in fact rounded central

The Japanese unrounded back vowel /ɯ/ is
in fact rounded central/front [ʉ - ʏ]
Akitsugu Nogita
Noriko Yamane
Sonya Bird
University of Victoria University of British Columbia University of Victoria
This study reports on an ultrasound and video recording investigation of the socalled unrounded back vowel /ɯ/ in Standard Japanese (SJ henceforth), as in /ɯɕiɾo/ ‘back’,
based on our hypothesis that /ɯ/ is underlyingly a rounded central vowel with lip
protrusion and the more appropriate phonemic IPA symbol is /ʉ/. As it turns out, the
tongue position of SJ /ɯ/ was closer to that of the front vowel /e/ than the back vowel /o/
by 6 of the 7 native SJ speaking participants, and all the 7 participants actively rounded their
lips; at least 4 of them also showed clear lip protrusion.
Background and research questions
In terms of lip rounding, linguists commonly treat SJ /ɯ/ as unrounded. In fact, the
prescriptive /ɯ/ is supposed to be with flat lips rather than rounded lips (Akiyama, 2009). In
contrast, Ito, Kang and Kenstowicz (2006) state that SJ /ɯ/ is produced with vertical lip
compression, or narrowing of the lips but without lip protrusion. As for backness, some
linguists treat both SJ /ɯ/ and /a/ as central vowels as opposed to the back /o/. In fact,
some acoustic studies, such as Hisagi, Nishi and Strange (2008), show that the second formant
(F2) of /ɯ/ is very close to that of /a/, rather than /o/, but F2 of /ɯ/ seems slightly lower
than that of /a/. If /ɯ/ is in fact central, the commonly used phonemic or broad
transcription /ɯ/ is inappropriate. Thus, this study questions whether native speakers of SJ
actively unround their lips as seen in the Korean /ɨ/ as in /hankɨl/ ‘Hangul’ and actively
back their tongue, as the symbol /ɯ/ indicates. More specifically, does /ɯ/ lack lip
protrusion as Ito et al. mention? Is the tongue posture of /ɯ/ articulatorily closer to back
vowels or front vowels?
To answer these questions, we had 7 linguistically naïve native SJ speakers
pronounce the short five vowels /i, e, a, o, ɯ/. Each phoneme was pronounced in isolation in
order to have the participants emphasize underlying features of each phoneme. The tongue
and lip movements were video-recorded with an ultrasound machine and a video camera.
Each phoneme was pronounced 12 times. The tongue shapes of each phoneme and rest
position were traced in EdgeTrak, and analyzed in R.
Results and discussion
The results indicate that /ɯ/ is actively rounded by all the participants, as opposed to
a rest position with no active rounding. At least 4 of the 7 participants showed clear lip
protrusion as shown in Figure 1 below.
The analysis of backness in the ultrasound images suggests that /ɯ/ is more front
than /a/ for all the speakers as shown in Figure 2. More interestingly, the tongue position of
/ɯ/ is closer to that of the front vowel /e/ than that of the back vowel /o/ by 6 out of the 7
participants (see Figure 2) and the rest of the speaker’s /ɯ/ is located almost in the middle
between /o/ and /e/. As well, /ɯ/ is closer to the rest position than other vowels. Moreover,
among 5 out of the 7 participants, the front part of the tongue of /u/ patterns together with
/i, e/ and the rest position rather than with /o, a/ as shown in Figure 3. These findings
suggest that /ɯ/ is central or even slightly front, rather than back.
To answer our questions, therefore, 1) /ɯ/ is underlyingly rounded and it can involve
lip protrusion, and 2) /ɯ/ is more front than the so-called central /a/, and typically closer to
/e/ than /o/. Thus, /ɯ/ is central but more towards the front than towards the back.
Therefore, a possible IPA for /ɯ/ in isolation is [ʉ], or possibly even [ʏ] in some cases (but
not as front as [y]). The reason why F2 of /ɯ/ is slightly lower than that of /a/ may be
caused by lip rounding.
Conclusion
To conclude, /ɯ/ is not the appropriate symbol for the phonemic transcription of
Standard Japanese. We propose the rounded central vowel /ʉ/: e.g. /ɯɕiɾo/ à /ʉɕiɾo/.
References:
Akiyama, K. (2009). Sensê seminar: Hatsuon hassê. NHK CTI Nihongo Centre.
Hisagi, M., Nishi, K., & Strange, W. (2008). Acoustic properties of Japanese and English
vowels: Effects of phonetic and prosodic context. In M. Endo-Hudson, S.-A. Jun, P.
Sells, P. M. Clancy, S. Iwasaki, and S. Sung-Ock, eds., Japanese/Korean Linguistics 13.
Stanford: CSLI.
Ito, C., Kang, Y., & Kenstowicz, M. (2006). The adaptation of Japanese loanwords into Korean.
MIT Working Papers in Linguistics 52: 65-104.
Figure 1. Lip protrusion in the “unrounded“ /ɯ/ by a female Standard Japanese speaker in
her 20’s and a male speaker in his 30’s.
M20A /ɯ/ vs. /o/
M20A /ɯ/ vs. /a/
M20A /ɯ/ vs. /e/
M20A /ɯ/ vs. the rest position
Figure 2. The tongue positions of /ɯ/ vs. /o/, /ɯ/ vs. /a/, /ɯ/ vs. /e/, and /ɯ/ vs. the
rest position by a male speaker in his 20’s (labeled as M20A).
F30B a i ɯ e o rest Figure 3. The average tongue contours of /a, i, ɯ, e, o/ and the rest position by a female
speaker in her 30’s (labeled as F30B).