In this work we present preliminary results from a large scale production study of American English liquids. MRI and ultrasound have been used to image 20 subjects producing /r/ and /l/. Subjects were native speakers, representative of the main American dialects, and balanced between sexes. MRI data were collected volumetrically for recovery of three-dimensional tongue shape. In addition, a short (1 s) midsagittal protocol was used in conjunction with ultrasound scanning to confirm the validity of the sustained production required for volumetric imaging. Our results show tongue shapes not inconsistent with the six main types found by Delattre and Freeman (1968), but their range and variety suggest that either additional canonical shapes or a different organizational principal (such as palatal shape) is motivated. We have also observed consistent patterns of tongue grooving associated with different midsagittal shapes, from the parasagittal data not accessible from the Delattre and Freeman cineradiography. In addition to this 3D-based taxonomy of /r/ tongue shapes we present similar data for lateral productions, and the associated acoustic structures for both. [Research supported by NIH.]
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Tiede et al. (2004) studied this question.