What is the role of vowel hyperarticulation in language learning?

Have you ever wondered why the way you talk to infants is so vastly different from how you talk to adults? Infant-directed speech (IDS) 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.   
 

Exaggerated vowel space has previously been correlated to speech intelligibility in IDS. It is exactly this acoustic aspect that was also observed in speech to adult foreigners. The observation of exaggerated vowel space in IDS and in foreigner-directed speech (FDS) can be understood in the context of the Hyper-HypoSpeech (H&H) 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.

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 maximise speech intelligibility. My PhD thesis explored the role of exaggerated vowel space in interaction with foreigners and infants. It suggests in line with the H&H theory 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. For more information, please check out my thesis at the link below. For a snapshot into this topic, you can take a look at the article from last year. 

Kangatharan, J. (2015). The role of vowel hyperarticulation in clear speech to foreigners and infants. Available at http://bura.brunel.ac.uk/handle/2438/10519  

Kangatharan, J. (2017). “Speech modifications aimed at enhanced intelligibility in the English language”. The Journal of The Queen’s English Society, 125, 46-48.