Effects of Variability on Japanese Learning of English /r/ and /l/ – David B. Pisoni (Indiana University at Bloomington)
In this talk I will focus on several general issues surrounding perceptual learning in speech perception. While my major interest centers on the learning of nonnative speech contrasts by mature adults, much of what I have to say is also relevant to other issues dealing with current theoretical accounts of speech perception and perceptual development. Central to my presentation is a concern for the nature of the perceptual changes that take place when the sound system of a language is acquired during development. In particular, we have been interested in what happens to a listener’s perceptual abilities when he or she acquires a native language. What happens to a listener’s ability to identify and discriminate speech sound contrasts that are not present in the language-learning environment? Are the listener’s perceptual abilities permanently lost because the neural mechanisms have atrophied due to lack of sensory stimulation during development, or are they simply realigned and only temporarily modified due to changes in selective attention? It is well known that native speakers of Japanese learning English generally have difficulty discriminating and categorizing the English phonemes /r/ and /l/, even after years of experience. Previous research that attempted to train Japanese listeners to distinguish this contrast using synthetic stimuli showed little success, especially when generalization to natural tokens containing /r/ and /l/ was tested. In this presentation, I describe the major results of an on-going research program on perceptual learning of speech sounds in non-native speakers of English. In all of our studies, we used a novel training procedure that differed from earlier attempts to modify Japanese listener’s perception of English /r/ and /l/. Japanese subjects were trained in an identification paradigm using multiple natural exemplars contrasting /r/ and /l/ phonemes from a variety of phonetic environments. A pretest-posttest design combined with tests of generalization containing novel natural tokens were used to assess the effectiveness of this “high-variability” training procedure. Analysis of data from several experiments showed that the new training procedure was much more effective than earlier techniques. Reliable differences were obtained in performance between pretest and posttest perception scores. Moreover, reliable differences were observed in several generalization tests which involved presentation of novel tokens of /r/ and /l/ that the subjects were never trained on. The best generalization performance was observed when subjects received novel words produced by a talker that they had heard during the training phase. Other perceptual learning experiments carried out at the ATR Labs in Kyoto, Japan with monolingual subjects replicated our original findings and assessed the retention and time-course of this learning. Finally, our most recent study examined the transfer of perceptual knowledge to control over production of /r/ and /l/ to assess perceptuo-motor interactions between speech perception and production. The results demonstrate the importance of stimulus variability in learning to perceive and produce novel phonetic contrasts that are not distinctive in a listener’s native language.