Modifications in speech to enhance intelligibility in the English language

What is the one tool that we use to solve problems and advance culture through the retention and transmission of knowledge? Exactly, it is language. What happens when we first learn a language? Early in life we appear to be able to differentiate between virtually all phonetic units in the world languages (Kuhl et al., 2008). And around the age of nine months infants adjust to the information of their native language. For example, cross-sectional and longitudinal studies showed that while 6-8 months old English infants distinguished between non-native consonant contrasts easily such as in the Hindi language, 10-12 months old infants had difficulty with this task (Werker & Tees, 1984a; Werker & Lalonde, 1988). Similarly, infants’ ability to distinguish between non-native vowel categories was reported to decrease as well (Werker & Tees, 1984a; Werker & Lalonde, 1988).

Thus, we can establish that our speech perception abilities undergo a binary modification towards the end of the first year of life (Kuhl et al., 2008). At around the same time in the English language, mothers talk to their infants in a way that has come to be known as motherese or infant-directed speech (IDS). Infant-directed speech involves acoustic changes such as increased mean pitch, increased emotional affect, and slow speech rate. Mothers also exaggerate the differences in the sound of vowels: Thus, if you have the words ‘sheep’, ‘shoe’ and ‘shark’, you will make the vowels ‘ee’, ‘oo’ and ‘aa’ sound more different from one another. This is known as increased vowel space (Kuhl, Andruski, Chistovich, Chistovich, & Kozhevnikova, 1997; Uther, Knoll, & Burnham, 2007).

All these acoustic changes are considered to facilitate language acquisition in infants. Prior research that compared IDS to clear read speech to test if those changes in IDS are uniquely didactic did indeed demonstrate increased vowel space in IDS compared to clear read speech (Kangatharan, 2016). Exaggerated vowel space has previously been correlated to speech intelligibility in IDS (Bradlow, Torretta, & Pisoni, 1996). It is exactly this acoustic aspect that was also observed in speech to adult foreigners (Uther et al., 2007).

The observation of exaggerated vowel space in IDS and in foreigner-directed speech (FDS) can be understood in the context of the Hyper-HypoSpeech theory by Lindblom (1990) according to which any changes in your speech signal are considerably influenced by who the listener is and what the speaking environment is. It is considered that speech production is a listener-oriented modification of speech. In this regard, the observation of exaggerated vowel space in IDS and FDS can be explained in the English language by the fact that both groups have the same linguistic needs (Uther et al., 2007). Thus, one can categorize these two groups as language learners as they are in clear need of an atypically clearer speech input, and speech with exaggerated vowel space is supposed to maximize speech intelligibility.

Recent research specifically found exaggerated vowel space to occur in speech to foreign-sounding rather than foreign-looking listeners (Kangatharan, 2016). This confirms in line with the H&H theory that speech is modified with regard to the listener’s linguistic needs rather than visual appearance. It was also demonstrated that speech with expanded vowel space resulted in increased speech intelligibility in both native English speakers and in second language learners of English in contrast to speech without expanded vowel space. The findings indicate that both first and second language learners of English can perceptually benefit from verbal adaptions in the English language if they have a didactic function (Kangatharan, 2016).

References

Bradlow, A. R., Torretta, G. M., & Pisoni, D. B. (1996). Intelligibility of normal speech. I. global and fine-rained acoustic-phonetic talker characteristics. Speech Communication, 20, 255–272.

 

Kangatharan, J. (2016). “The role of vowel hyperarticulation in clear speech to foreigners and infants: PhD Thesis publication.” European Acoustics Association Young Acoustics Network Newsletter, 47, Issue 2, 4-5.

Kuhl, P.K., Andruski, J.E., Chistovich, I.A., Chistovich, L.A., Kozhevnikova, E.V., Ryskina, V.L., Stolyarova, E.I., Sundberg, U., & Lacerda, F. (1997). Cross-language analysis of phonetic units in language addressed to infants. Science, 277, 684–686.

Kuhl, P. K., Conboy, B. T., Coffey-Corina, S., Padden, D., Rivera-Gaxiola, M., & Nelson, T. (2008). Phonetic learning as a pathway to language: New data and native language magnet theory expanded (NLM-e). Philosophical Transactions of the Royal Society B, 363, 979-1000.

Lindblom, B. (1990). ‘Explaining phonetic variation: A sketch of the H&H theory’, 403-439 in Hardcastle W J & Marchal A (eds): Speech Production and Speech Modeling, Dordrecht:Kluwer.

Uther, M., Knoll, M. A., & Burnham, D. (2007). Do you speak E-NG-L-I-SH? A comparison of foreigner- and infant-directed speech. Speech Communication, 49, 2-7.

Werker, J. F., & Tees, R. C. (. (1984a). Cross-language speech perception: Evidence for perceptual reorganization during the first year of life. Infant Behavior and Development, 7, 49-63. 

Werker, J. F., & Lalonde, C. E. (1988). Developmental Psychology, 24, 672-683.