13 Jul 2004

Simone Ashby Hanna (University College Dublin)

This research investigates whether properties of speech to infants may be classified as hyperspeech modifications, as defined by Lindblom's H&H Theory. Hyperspeech is defined as an attempt by speakers to meet listeners' communicative and situational demands by increasing the distinctiveness of speech sounds for enhanced lexical identification. Previous research has presented infant-directed (ID) speech as an accommodative style whose acoustic features provide babies with structured input for making sense of speech and acquiring mappings between sound and meaning. Implicit in some of these claims is the notion that ID speech is better formed---i.e. it involves hyperarticulation as per Lindblom's definition---compared to adult-directed speech. Yet, with most investigations focused on effects of this style on infants' perceptual abilities, little quantitative information is available for the ID speech signal itself. This thesis aims to describe the acoustic properties of ID speech, and evaluate the systematicity of such variations with respect to other accommodative styles.

By comparing ID speech with other listener-oriented styles, two questions are addressed. First, do different listener constraints elicit characteristic forms of modulation by speakers? Few studies have examined how listener constraints interact with modulation of the signal. Results for this investigation show that for experimental conditions representing computer-directed speech, 'foreigner talk', and Lombard speech, subjects varied systematically depending on the type of listener being addressed. In contrast, for both simulated and real ID speech conditions, speakers exercised considerable flexibility in the manipulation of selected acoustic parameters. Second, how does ID speech compare with other accommodative styles in the use of hyperspeech? I conclude that ID speech may involve production of clear speech features, but that unlike speech to an artificial or non-native addressee (i.e. other modalities involving conceptual and/or linguistic constraints on the part of the interlocutor), use of such features is far less consistent across speakers.

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