Language Evolution and Computation Bibliography

Phonologies are characterised by regularity, from the stereotyped phonetic characteristics of allophones to the contextually conditioned alternations between them. Most models of grammar account for regularity by hypothesising that there is only a limited set of symbols for expressing underlying forms, and that an independent grammar algorithm transforms symbol sequences into an output representation. However, this explanation for regularity is called into question by research which suggests that the mental lexicon records rich phonetic detail that directly informs production. Given evidence for biases favouring previously experienced forms at many levels of production and perception, I argue that positive feedback within a richly detailed lexicon can produce regularity over many cycles of production and perception. Using simulation as a tool, I show that under the influence of positive feedback, gradient biases in usage can convert an initially gradient and variable distribution of lexical behaviours into a more categorical and simpler pattern.

Evidence supporting a rich memory for associations suggests that people can store perceptual details in the form of exemplars. The resulting particulate model of category contents allows the application of evolution theory in modeling category change, because variation in categorized percepts is reflected in the distribution of exemplars in a category. Within a production-perception feedback loop, variation within an exemplar-based category provides a reserve of variants that can serve as the seeds for shifts in the system over time through random or selection-driven asymmetries in production and perception. Here, three potential pathways for evolutionary change are identified in linguistic categories: pruning of lines of inheritance, blending inheritance and natural selection. Simulations of each of these pathways are shown within a simple exemplar-based model of category production and perception, showing how consideration of evolutionary processes may contribute to our understanding of linguis...

Generative models of phonology account for output patterns through a complex grammar applied over a minimal lexicon. In contrast, many natural complex patterns result from the gradual accumulation of structure through repeated local interactions. In this dissertation I present results of simulations supporting the proposal that some phonological patterns can be accounted for through self-organization within an analogically structured lexicon, in response to forcing from external biases. In Chapter 1, I show that patterns accounted for by the Optimality-Theoretic principles of constraint dominance and strict constraint dominance can be shown to spontaneously arise in analogically-structured systems, driven by competition between leveling pressures within the lexicon and differentiating pressures from lexicon- external performance biases.

Phonological systems exhibit `constrained contrast' in two distinct ways: first, phonologies exhibit only a subset of cross-linguistically attested contrasts, formed from a subset of possible features in combination. Second, crosslinguistically infrequent elements also tend to occur less frequently in a language that does have them. In Chapter 2, I present evidence that both of these patterns can be accounted for diachronically through indirect selection over phonetic variants, given the assumptions that, 1) lexical categories are richly specified, 2) a perceived utterance updates the content of a lexical category only if it is identified as an example of that lexical category, and 3) lexical categories can influence each others' production in proportion to phonological similarity.

When a simulated speaker/hearer pair alternately communicate their lexicons to each other under these conditions their lexicons converge. Further, when an output is too close to multiple categories, it is less likely be consistently categorized, with the result that it has less influence on the evolution of the pairs' lexicons, resulting in pressure on lexical categories to remain contrastive. W hen biases against certain features or feature combinations are introduced, the pairs' lexicons evolve to avoid as many of these `less-fit' elements as possible. However, when avoidance of all marked elements would result in insufficient contrast, the lexicons evolve to utilize a subset of less-fit elements, but at a lower frequency than fitter elements.

One of the most salient properties of phonological systems are their very consistency. This paper describes work suggesting that such categorical behavior in phonological systems can be modeled as an emergent property resulting from self-organization (Nicolas and Prigogine 1977) within an iterating, richly-specified lexicon.