Tonal disruption in the speech of a language-delayed Thai adult

Abstract

An acoustic-perceptual investigation was performed on fundamental frequency (F(0)) contours associated with lexical tones in the speech of one 21-year-old adult speaker of Thai who did not start speaking until age 7. Thai is a tone language with five lexically contrastive tones-mid, low, falling, high, and rising. Measures of F, were taken from a minimal set of five monosyllabic citation forms. Results from phonemic identification tests indicated that AY exhibited a selective disruption in the production of Thai tones. In contrast to the normal Thai tone space, AY's tone space was reduced to three tones-mid, low, and rising. Acoustic analysis revealed that AY�s aberrant F(0) contours for the falling and high tones were virtually identical in terms of height and overall shape; both exhibited a slow, steady fall in F(0) in the upper range of AY's tone space. Listeners' failure to perceive AY's intended productions of the falling and high tones confirmed the perceptual importance of rapid change in F(0) slope in the Thai tone space. Findings are discussed with reference to the chronological order in which Thai tones are acquired in normal language development.