|Modelling the perceptual development of phonological contrasts with OT and the Gradual Learning Algorithm
|Paola Escudero, Paul Boersma
|Published (2003) in Proceedings of the 25th Annual Penn Linguistics Colloquium.
|One of the tasks of the language acquisition process is to optimize strategies for comprehension. For speech perception, this means that the learner has to establish an accurate mapping from acoustically detailed input to discrete phonological categories. As an example, this paper considers the development of the perception of the English vowels /I/ and /i/ in native speakers.
Production-wise, the two vowels differ in various respects. Here, we limit ourselves to considering duration and the first formant (F1). It turns out that the use of these two acoustic dimensions in production depends on the dialect at hand: for Scottish English speakers, /I/ and /i/ differ much more in F1 and much less in duration than for Southern English speakers.
We hypothesize that humans have an optimal perception strategy that minimizes the probability of confusion and that there is a knowledge that underlies the implementation of this strategy. We model the knowledge behind speech perception as an Optimality-Theoretic perception grammar, and we model the acquisition of this knowledge with the Gradual Learning Algorithm. Using an environment based on real production data, we simulate the development of a Scottish and a Southern English listener, and show that the Scot comes to rely almost exclusively on height (F1) when distinguishing /I/ and /i/, whereas the Southerner comes to rely on both height and duration, so the model indeed implements an optimal strategy for acoustic cue integration. Perception experiments show that real Scots and real Southerners also use this optimal strategy in their own environments.
We find, therefore, that perceptual strategies depend on the production environment, and that we can successfully model this dependency within the framework of stochastic Optimality Theory, thus bringing speech-processing systems within the reach of formal phonological theory.