PLASER is a multimedia tool with instant feedback designed to teach English pronunciation for high-school students of Hong Kong whose mother tongue is Cantonese Chinese. The objective is to teach correct pronunciation and not to assess a student’s overall pronunciation quality. Major challenges related to speech recognition technology include: allowance for non-native accent, reliable and corrective feedbacks, and visualization of errors.

PLASER employs hidden Markov models to represent position-dependent English phonemes. They are discriminatively trained using the standard American English TIMIT corpus together with a set of TIMIT utterances collected from “good” local English speakers. There are two kinds of speaking exercises: minimal-pair exercises and word exercises. In the word exercises, PLASER computes a confidence-based score for each phoneme of the given word, and paints each vowel or consonant segment in the word using a novel 3-color scheme to indicate their pronunciation accuracy. PLASER was used by 900 students of grade 7 and 8 over a period of 2–3 months. About 80% of the students said that they preferred using PLASER over traditional English classes to learn pronunciation. A pronunciation test was also conducted before and after they used PLASER. The result from 210 students shows that the students’ pronunciation skill was improved.(The statistics is significant at the 99% confidence level.)