An MRI study of the effect of vowel context on English fricatives

To gain a better understanding of the long-observed effects of vocalic context, the articulation of fricatives was investigated using Magnetic Resonance Imaging. Five speakers of American English were imaged while producing eight fricatives in the contexts /i-a-u-∂/. Sagittal, axial and oblique-coronal volumes were acquired for each vowel-fricative combination. Acoustic recordings were made during scans and separately in an anechoic chamber. Vocal tract models were generated by aligning and superimposing all three stack orientations. The models reveal that a variety of articulatory strategies are employed in the production of English fricatives, and that vocalic context is significant. For some subjects, tongue shape differs little with vowel context; other subjects show highly varied tongue shape differences but little difference in lip rounding. Two subjects show significant variation with vowel context for every fricative, including [θ]. Two show very little difference, even for [f]. The sublingual cavity in [∫] is extensive for two subjects, but only slightly bigger than in [s] for two other subjects. Tongue grooving in and behind the constriction also varies, and is especially evident in the oblique scans. Overall, more variation and effect of vowel context was observed than expected from the literature.