Support for the feature “Expanded”: An MRI analysis of Akan +/−ATR vowel pairs

The Akan language has a harmony system bifurcating its vowel inventory into two complimentary sets. Previous work by Lindau [J. Phon. 7, 163–176 (1979)] has shown that these sets are distinguished by tongue root position (ATR) and larynx height, and she proposed a feature “Expanded” to characterize the relevant difference in phayrngeal volume. Lindau's measurements were based on cineradiographic tracings of the sagittal midline only; the purpose of the current study was to exploit magnetic resonance imaging to obtain (axial) images of cross sections through the pharynx for vowels in the contrasting vocal tract configurations. Sagittal and axial image data were obtained for three vowel pairs: /i/:/ɪ/,/e/:/ɛ/, and /u/:/ɷ/. Subjects were scanned while phonating continuously with constant pitch and vowel quality, with a recording of the target vowel playing continuously through an earphone. A sound recording was made of vocal output to verify subjects remained on target. The results obtained show that Akan does rely on tongue root advancement and a lowered larynx for the harmony contrast, but also show that pharyngeal lateral width varies systematically as well. This confirms Lindau's observation that pharyngeal volume rather than tongue root position alone is the distinguishing characteristics. [Work supported by NIH Grant DC‐00121.]