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                                AU, CHING-PONG
          Dynamique Du Langage, UMR 5596 CNRS, Université Lyon 2, ISH
                14 avenue Berthelot 69363 Lyon Cedex 07, France

A computational model linking up developmental properties and sound changes
was built, in order to seek for possible solutions for some controversial issues
about the implementation of sound changes (Au, 2005). In the model, there is a
population of agents. Each of them has a cognitive structure with four internal
subsystems (perception, decoding, coding and production). The subsystems of
the agents develop individually during development. The formation of
perceptual categories is driven by statistical distributions of sounds that the new-
born agents have listened to (e.g. Maye et al, 2002). A self-organizing map is
used to simulate the category formation (Guenther et al, 1996).
     In the simulation results of the model, two seemingly contradicting
hypotheses on sound change transitions Neogrammarian regularity (lexically
regular; Osthoff et al, 1878) and lexical diffusion (lexically irregular; Wang,
1969), can both be observed under different conditions. During a shift, the
pronunciations of the lexical items change regularly as described in the
Neogrammarian hypothesis; during a merger, the spoken forms display a regular
pattern at the beginning, and then become irregular lexically as described in
lexical diffusion. These conditions are primarily matched with the empirical data
supporting the two opposing hypotheses. With further investigation on the
subsystems of the agents, the consistency of perceptual responses among
agents was found to be the causes of different transition patterns. At the later
stage of a merger of two sounds, when two groups of words become acoustically
close, the perceptual responses of individual agents become inconsistent
throughout the population due to the statistically determined nature of perceptual
development. The locations and the sharpness of boundaries between two
categories vary and some agents may even have only one category across the
acoustic range of the two original sounds. As the word pronunciations are learnt
through self-listening, the spoken forms of various words are scattered along the
acoustic range of the two original sounds. This is the basis of the irregularity; but
when a perceptual category is still far enough from the neighboring categories,
the category formed of each agent is similar and stable as in the shifts or the
beginning stages of mergers. All spoken forms of the words in the same group
are picked within the same small phonetic range bounded by the perceptual
category. The category location in the acoustic domain may differ slightly from
generation to generation. When the acoustic differences accumulate, it appears
that the spoken forms under the same perceptual category change simultaneously
and gradually in the same direction as described in the Neogrammarian

     In conclusion, the model here provides a more precise description on how
the phonological systems evolve from time to time. If the present model is able
to describe the reality appropriately, it can be potentially extended into a model
that provides insights for the emergence of phonological systems.

Au, Ching-Pong (2005), Acquisition and Evolution of Phonological Systems.
   PhD Dissertation. City University of Hong Kong.
Guenther F. H. and Gjaja M. N. (1996), The Perceptual Magnet Effect as an
   Emergent Property of Neural Map Formation. Journal of the Acoustical
   Society of America, 100, pp. 1111-1121.
Maye, J., Werker, J.F., & Gerken, L. (2002), Infant Sensitivity to Distributional
   Information Can Effect Phonetic Discrimination. Cognition, 82(3), B101-
Osthoff, H. and Brugmann, K. (1878), Morphologische Untersuchungen auf dem
   Gebiete der indo-germanischen Sprachen, Vorwort I. iii-xx. (English
   Translation in Lehmann 1967)
Wang, W. S-Y. (1969), Competing Changes as a Cause of Residue. Language.

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