Graduation Year

2007

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Speech-Language Pathology

Major Professor

Catherine L. Rogers, Ph.D.

Committee Member

Jean Krause, Ph.D.

Committee Member

Stefan Frisch, Ph.D.

Keywords

Intelligibility, Perception, Production, Second language, Communication

Abstract

'Clear speech' is a speaking style that talkers often employ when they know they may have trouble being understood, as when speaking in noise or to a person with a hearing loss. When 'clear speech' produced by native talkers is presented in noise to native listeners, it has been shown to be about 10-15 percentage points more intelligible, on average, than normally produced speech. Recent research has shown that bilingual listeners may experience a smaller intelligibility benefit than monolingual listeners from 'clear speech' produced by monolingual talkers. The present study compares the ability of monolingual and bilingual talkers to produce this clear speech intelligibility benefit.

The present study investigates the hypothesis that bilinguals may produce a smaller intelligibility benefit than monolinguals when asked to speak clearly. Three groups of talkers were recorded: 13 monolingual native English speakers, 22 'early' Spanish-English bilinguals, with an age of onset of learning English (AOL) of 12 or earlier, and 14 later Spanish-English bilinguals, with an AOL of 15 or later. Talkers produced the target words "bead, bid, bayed, bed, bad" and "bod" in both clear and conversational speech styles. Two repetitions of each word were mixed with noise and presented to monolingual English-speaking listeners across two days of testing.

Both monolingual and early bilingual talkers showed a similar degree of clear speech benefit in noise (about 5.5%). Later bilinguals were the least intelligible overall and showed a smaller overall clear speech benefit in noise. Surprisingly, early bilinguals were significantly more intelligible than monolinguals in both speaking conditions (by about 6.5%). For the later bilinguals only, performance was significantly worse for one target word ("bid") in the clear speech condition than in the normal speech condition.

These data suggest that later bilinguals, but not early bilinguals, may experience a relative disadvantage when speaking in noise, due to a reduced ability to improve intelligibility by speaking more clearly. Therefore, these persons may benefit from communication strategies or accent reduction programs designed to increase their ability to make themselves understood in difficult speaking environments.

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