The Perception of Laryngeal and Length Contrasts in Early Language Acquisition

phonological level.39 Consequently, phonetics and phonology are very closely interlocked – in other words, Pierrehumbert (2003) assumes a direct continuity between phonetic and phonological representations.40 The exemplar-theoretic approach implies that abstract phoneme categories emerge from language-specific implementations of speech (including also prosodic properties like, e.g., stress). Consequently, phonological categories cannot be universal or even innate. A crucial aspect of the categories as suggested by this usage-based account is that they are flexible and can remain so for a very long time, becoming increasingly refined with age. Regarding the formation of phoneme categories in early childhood, Pierrehumbert (2003:132f.) states: “Through incremental experience, listeners acquire more and more accurate estimates of both the center of any given category distribution and the behavior of the tails of the distribution. This leads to more and more adult-like boundaries and patterns of variation. [. ] Each category is continually updated as the speaker perceives and encodes incoming examples; the updated distributions then provide the basis for productions by the speaker. ” Like Fikkert (2005a), Pierrehumbert (2003) suggests that infants start learning phoneme categories by ‘token statistics’, that is, by evaluating statistical distributions of phonetic properties in the speech signal. At a later point in development, when children already have (emerging) lexicons, phonological acquisition is supported also by ‘type statistics’ in the form of generalisations over the lexicon. Within Pierrehumbert’s (2001, 2003) exemplar-theoretic account, infants’ language-adapted perception of phones at the end of the first year of life suggests that the children already had sufficient experience with their mother tongue to establish native categories for these particular sounds. At the same time the process of phoneme acquisition is not completed at the age of 12 months. The model permits (and predicts) ongoing refinement and maturation, which is assumed to develop differently for individual sounds, depending on factors like salience and frequency. By assuming that abstract categories emerge from detailed phonetic representations, Pierrehumbert’s (2001, 2003) account of phonological acquisition resembles the template model (Vihman 2010; Menn & Vihman 2011). Nonetheless, the accounts differ in some crucial assumptions. Phonetics and The exemplar-theoretic model of category formation implies that categories need not be restricted to segments. Other aspects of the language, as for instance tones, syllables and feet can also be grouped into categories (see Pierrehumbert 2003:119f.). Since phonetics and phonology cannot be clearly separated in this model, the following paragraphs speak of ‘phoneme categories’ instead of explicitly referring to phonology. 112 4 Acquiring Phoneme Contrasts phonology are much more interlocked in the exemplar-theoretic account and due to the continuous updating of categories they also remain so in the course of development.41 Additionally, Pierrehumbert’s (2001, 2003) model allows to assume that the language-specific perception of speech at the end of the first year of life indicates that infants have established phoneme categories despite the absence of a (reasonably large) lexicon and that these permanently refined and updated categories will be used in word learning later. Thus, the exemplar-theoretic model of category formation is compatible with the processing-load explanations to the ‘bin/din-paradox’ whereas Menn & Vihman’s (2011) approach, which assumes that phonological systems are acquired only with a certain vocabulary size, rather suggests processing difficulties due to a lack of phonological structures.