Implications of an exemplar-theoretic model of phoneme genesis: a velar palatalization case study.

AbstractDiachronic velar palatalization is taken as the case study for modeling the emergence of a new phoneme category. The spread of a palatalized variant through the lexicon is treated as a stochastic classification task for the listener/learner. The model combines two measures of similarity to determine classification within an exemplar-theoretic framework: acoustic distance and phonotactic expectation. There are three model outcomes: contrast, allophony, or contextual neutralization between the plain and palatalized velars. It is shown, through a series of simulations, that these can be predicted from the distribution of sounds within the pre-change lexicons, namely, the ratio of the /k-vowel/ sequences containing naturally palatalizing vowels (i, I, e), to those containing non-palatalizers. "Unnatural" phonotactic associations can arise in individual lexicons, but are sharply limited due to the large size of the lexicon and the local nature of the phoneme changes. "Anti-natural" distributions, which categorically violate the proposed implicational relationship between palatalization and frontness/height, are absent. This work provides an explicit and restrictive model of phoneme change. The results also serve as an existence proof for an outcome-blind mechanism of avoiding over-generation.Keywordsexemplars, sound change, simulation, universals, evolutionary phonology(ProQuest: ... denotes formulae omitted.)IntroductionThis paper describes an exemplar-based computational model of language change. The model is developed in order to test the predictions of a general class of emergentist theories of linguistics. We ask if the range of synchronic grammars produced by running the model repeatedly under different conditions is an accurate reflection of the known typology. One objection to the emergentist approach stems from the belief that such models would over-generate unnatural and anti-natural grammars - unattested patterns that do not conform with posited language universals (de Lacy, 2006; Kingston & de Lacy, 2006; Kiparsky, 2006, 2008).The model chosen is one that is judged to be among the simplest instantiations that still includes the elements necessary to test the theoretical questions of interest. A dissimilation-based sound change supplies the necessary non-phonetically motivated segment sequences. The element of chance is provided by a sufficiently large lexicon to which sound changes are stochastically applied, and a top-down pressure from a phonotactic grammar allows fortuitous segment associations to persist. The model adopts a basic exemplar framework where individual word and sound tokens are stored in memory and directly affect perception (categorization) and production (e.g., Bybee, 2002; Goldinger, 1996; Luce, 1986; Nosofsky, 1988; Pierrehumbert, 2001). The phonotactic grammar, in turn, is assumed to derive from computations over the abstract categories to which the tokens belong.A series of simulations using this model elaborate the historic conditions under which certain types of synchronic segmental relationships will arise: contrastive, allophonic, or neutralizing. In addition, it is found that this simple - but, in certain ways, sufficient - model produces a relatively narrow typology; it does not significantly over-generate. This provides a concrete example - an existence proof - of a means of restricting synchronic grammars that does not rely on innate substantive restrictions.In addition, this work brings together usually disparate strands of research involving historic change and diffusion, exemplar theory, synchronic phonological representations, and the methodology of computational modeling. In so doing, the assumptions necessary to create a consistent and coherent theory of the transition from phonetic variation to phonological alternation are highlighted. Rather than provide definitive answers to long-standing questions within theoretical linguistics - both synchronic and diachronic - this work provides clear predictions that can be traced to particular features of the chosen model. …