The Relevance of Context and Experience for the Operation of Historical Sound Change

This paper is concerned with explaining how historical sound change can emerge as a consequence of the association between continuous, dynamic speech signals and phonological categories. The relevance of this research to developing socially believable speech processing machines is that sound change is both cognitive and social and also because it provides a unique insight into how the categories of speech and language and dynamic speech signals are inter-connected. A challenge is to understand how unstable conditions that can lead to sound change are connected with the more typical stable conditions in which sound change is minimal. In many phonetic models of sound change, stability and instability come about because listeners typically parse—very occasionally misparse—overlapping articulatory movements in a way that is consistent with their production. Experience-based models give greater emphasis to how interacting individuals can bring about sound change at the population level. Stability in these models is achieved through reinforcing in speech production the centroid of a probability distribution of perceived episodes that give rise to a phonological category; instability and change can be brought about under various conditions that cause different category distributions to shift incrementally and to come into contact with each other. Beyond these issues, the natural tendency to imitation in speech communication may further incrementally contribute to sound change both over adults’ lifespan and in the blending of sounds that can arise through dialect contact. The general conclusion is that the instabilities that give rise to sound change are an inevitable consequence of the same mechanisms that are deployed in maintaining the stability between phonological categories and their association with the speech signal.