Intelligibility of foreign-accented words: Acoustic
distances and gradient foreign accentedness
Vincent Porretta and Benjamin V. Tucker
University of Alberta, Department of Linguistics
Background
Overall Intelligibility
• Intelligibility and accentedness are related and at least partially
correlated dimensions of non-native speech [2].
• Highly accented speech does not necessarily preclude full
intelligibility of utterances [4].
• Average transcription accuracy (range: 0–1, M = 0.73, SD = 0.32)
• Average participant performance (range: 0.58–0.88, M = 0.72, SD
= 0.07).
• Acoustic distance of formant values affects intelligibility of English
vowels produced by native Japanese speakers [3].
Intelligibility and Acoustic Distances
• Word duration in non-native speech varies from native distributions
[1] and vowel duration has been shown to influence identification
of vowels produced by non-native speakers [3].
• Transcription accuracy modeled using binomial GAMM
• Temporal (durational) and spectral distances influence ratings of
degree of foreign accentedness [5].
Questions
• Do temporal and spectral distance measures affect single word
intelligibility?
• What is the functional relationship between intelligibility and
degree of foreign accentedness?
• Vowel-to-Word Ratio distance: As the durational relationship
deviates from a typical native production, the less likely the word
will be transcribed correctly
Methods
• Log F1 Distance: As F1 moves farther from an average native
value, the less likely the word will be transcribed correctly
Auditory tokens
• 40 English monosyllabic words [6] produced by:
• 9 native Chinese speakers
Intelligibility and Accentedness
• 1 native English speaker
Participants
• Mean item intelligibility (logit transformed) modeled using GAMM
• 120 native English speakers
Task
• Orthographic transcription in E-prime
• Each participant completed 1 of 10 counterbalanced lists
• Accuracy scored automatically and checked by hand
Accentedness ratings
• Represent continuum of accent strengths: 1 (native) to 9 (nonnative) obtained from a previous study [5]
Acoustic distances
• Variables considered: Log formant values (F1–F3) and vowel-toword ratio (vowel duration over word duration)
• Native Acoustic Reference: average value of 6 native English
speakers not included as talkers in the experiment
• Accentedness Rating: As accentedness increases, intelligibility
decreases non-linearly, with higher ratings being more detrimental
to the intelligibility of the word
• Distance: The absolute value of the difference between a given
token and the Native Acoustic Reference value
Conclusions
Analyses
• Generalized additive mixed modeling (GAMM), which does not
assume a linear relationship with possible non-linear functional
forms estimated based on the data [7]
• Temporal and spectral distances influence intelligibility, likely due
to misrecognition of the vowel and non-native-like durational
relationship among phonemes.
• Listeners appear sensitive to probable values along multiple
phonetic dimensions, influencing the likelihood of correct
identification of variable productions.
References
[1] Baker, R. E., Baese-Berk, M., Bonnasse-Gahot, L., Kim, M., Van Engen, K. J. & Bradlow, A. R. 2011. Word durations in non-native English. J.
Phon., 39(1), 1–17.
[2] Derwing, T. M. & Munro, M. J. 1997. Accent, Intelligibility, and Comprehensibility. Stud. Second Lang. Acquis., 20(1), 1–16.
[3] Kewley-Port, D., Akahane-Yamada, R., & Aikawa, K. 1996. Intelligibility and Acoustic Correlates of Japanese Accented English Vowels. Proc. of
ICSLP 96, 450–453.
[4] Munro, M. J. 1993. Productions of English vowels by native speakers of Arabic: Acoustic measurements and accentedness ratings. Lang. and
Speech, 36(1), 39–66.
[5] Porretta, V., Kyröläinen, A.-J., Tucker, B. V. In press. Perceived foreign accentedness: Acoustic distances and lexical properties. Atten Percept
Psychophys, 1–14.
[6] Van Engen, K. J., Baese-Berk, M., Baker, R. E., Choi, A., Kim, M., & Bradlow, A. R. 2010. The Wildcat corpus of native-and foreign-accented
English: Communicative efficiency across conversational dyads with varying language alignment profiles. Lang. and Speech, 53(4), 510–540.
[7] Wood, S. N. 2006. Generalized additive models: An introduction with R. Boca Raton: Chapman & Hall/CRC Press.
18th International Congress of Phonetic Sciences
• The inverse relationship between intelligibility and foreign
accentedness appears to be non-linear, with strong accent ratings
being particularly disruptive to intelligibility.
• Outside an effect of sentential context, the identification of words
is influenced by specific relative acoustic properties and perceived
degree of foreign accentedness.
Glasgow, UK: 10–14 August 2015
[email protected]