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Simulating the evolution of consonant inventories Mackie, James Scott


A major question in phonology concerns the role of historical changes in shaping the typology of languages. This dissertation explores the effect of sound change on consonant inventories. Historical reconstruction is mainly done by comparing cognate words across languages, making it difficult to track how inventories change specifically. Additionally, few languages have historical written records that can be directly examined. For this dissertation, the main research tool is computer simulation, using bespoke software called PyILM, which is based on the Iterated Learning Model (Kirby 2011, Smith et al. 2003). This allows for the simulation of sound change from arbitrary starting points, controlling for a multitude of variables. PyILM is an agent-based model, where a 'speaking' agent transmits a set of words to a 'listening' agent. The speaking agent is then removed, the learner becomes the speaker, and a new learner is introduced. The cycle repeats any number of times, roughly simulating the transmission of language over many generations. Sound change in a simulation is due to channel bias (Moreton 2008), the result of which is that agents occasionally misinterpret some aspect of speech, and internalize sound categories that differ from the previous generation (Ohala 1981, Blevins 2004). Three typological generalizations are examined, none of which have previously been studied from an evolutionary perspective: (1) The total number of consonants in a language. This is shown to be related to syllable structure, such that languages with simple syllables develop smaller inventories than languages with complex syllables. This mirrors a positive correlation between inventory size and syllable structure in natural languages, as reported by Maddieson (2007). (2) The correlation reported by Lindblom and Maddieson (1988) between the size of an inventory and the complexity of its segments. This effect emerges in simulations when context-free changes are introduced, since these changes produce similar outcomes in inventories of all sizes. (3) Feature economy (Clements 2003), which refers to the way that consonants within a language tend to make use of a minimal number of distinctive features. Economy emerges over time when sound changes take scope over classes of sounds, rather than targeting individual sounds.

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