Computer support for learners of spoken English

Abstract

This thesis concerns the use of speech technology to support the process of learning the English language. It applies theories of computer-assisted language learning and second language acquisition to address the needs of beginning, intermediate and advanced students of English for specific purposes. The thesis includes an evaluation of speech-recognition-based pronunciation software, based on a controlled study of a group of immigrant engineers. The study finds that while the weaker students may have benefited from their software practice, the pronun¬ciation ability of the better students did not improve. The linguistic needs of advanced and intermediate Swedish-native students of English are addressed in a study using multimodal speech synthesis in an interactive exercise demonstrating differences in the placement of lexical stress in two Swedish-English cognates. A speech database consisting of 28 ten-minute oral presentations made by these learners is described, and an analysis of pronunciation errors is pre¬sented. Eighteen of the presentations are further analyzed with regard to the normalized standard deviation of fundamental frequency over 10-second long samples of speech, termed pitch variation quotient (PVQ). The PVQ is found to range from 6% to 34% in samples of speech, with mean levels of PVQ per presentation ranging from 11% to 24%. Males are found to use more pitch variation than females. Females who are more proficient in English use more pitch variation than the less profi¬cient females. A perceptual experiment tests the relationship between PVQ and impressions of speaker liveliness. An overall correlation of .83 is found. Temporal variables in the presentation speech are also studied. A bilingual database where five speakers make the same presentation in both English and Swedish is studied to examine effects of using a second language on presentation prosody. Little intra-speaker difference in pitch variation is found, but these speakers speak on average 20% faster when using their native language. The thesis concludes with a discussion of how the results could be applied in a proposed feedback mechanism for practicing and assessing oral presentations, concept¬ualized as a ‘speech checker.’ Potential users of the system would include native as well as non-native speakers of English.

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