A fundamental aspect of human cognition is the capacity to perceive and produce language. Studies of non-native speech processing provide some of the most striking evidence bearing on this capacity: when humans attempt to perceive or produce words containing foreign sounds or sound sequences, they show systematic patterns of correct and incorrect performance. Prior research has established that different non-native structures elicit different rates and types of error; it has been hypothesized that these differences can be explained by a combination of grammatical, perceptual, and articulatory factors. The main goals of this project are to provide carefully controlled experimental evaluations of these factors, and to develop an explicit, probabilistic model of how they interact in human performance. Particular experimental issues to be investigated are: (1) what phonetic characteristics humans are most sensitive to when processing non-native sounds; (2) how the quality of the input and ambient acoustics affect non-native perception and production; and (3) whether learning word meaning can modulate sensitivity to detailed properties of non-native sounds. The computational model builds on a growing body of work suggesting that human perception and action reflect optimal Bayesian inference conditioned on prior expectations and noisy sensory measurements. The relevant prior reflects knowledge of the native language; the model predicts that non-native structures that are more similar to those in the native language should be processed with greater accuracy. The model also predicts that non-native sounds with robust perceptual properties should be processed more accurately, even if their prior probabilities are low. The development of this model, which will be made available to other researchers, will promote the role of phonology and phonetics within the broader context of cognitive science research. Because our experiments examine the impact of classroom acoustics and talker variation on non-native sound processing, this project also has ramifications for foreign language pedagogy.
