Acquisition and evolution of phonological systems

Abstract

A dynamic computational model linking up the cognitive-developmental properties of the human beings (local mechanisms) and the transition patterns of sound changes (global phenomena) was built, in order to seek for possible solutions to resolve the controversial issues about the implementation of sound changes. In the simulation results of the model, two controversial sound change transition patterns, Neogrammarian regularity and lexical diffusion, can both be found under different conditions. During a shift without fusion of sounds, the pronunciations of the lexical items change regularly as described in the Neogrammarian hypothesis; during a merger, the spoken forms display a regular pattern as in a shift at the beginning. Then the changing patterns become irregular lexically as described in lexical diffusion, when the two perceptual categories are fusing together. These conditions are primarily matched with the empirical data reported in literatures. Besides the coexistence of the two controversial patterns, the simulation results also support the existence of another controversial phenomenon, near-merger: individual speakers in the population cannot perceptually distinguish two sounds but can produce them differently. The present model provides a reasonable explanation to the coexistence of Neogrammarian regularity and lexical diffusion. To build such a model, it is necessary to replace a few inveterate assumptions in phonology. They include: (1) symmetry between perception and production; (2) irrelevance of phonetics; and (3) discreteness of boundaries. In the present model, perception and production develop individually in different cognitive subsystems in different time, so perception and production are not necessary to be the same. Moreover, instead of using abstract symbols to represent internal phonemes, the internal sound units are defined in two continuous cognitive domains: perceptual domain and articulatory domain. Thus some phonetic information can be retained internally in the two domains. Finally, no perceptual categories with infinitely sharp perceptual boundaries are assumed in the model. The formation of perceptual categories is driven by statistical distributions of sounds that the infants listened to.