Articulatory overlap in English syllables with postvocalic /ɹ/

In General American English (GAE), only two full vowels [ɑ, ɔ] occur in syllables ending in [ɹ] plus a non-coronal consonant, e.g. <harp>, <pork>. An articulatory study of rhotic production by three speakers of GAE was conducted using real-time structural Magnetic Resonance Imaging (rtMRI) (Narayanan et al. 2004). Subjects produced /ɹ/ in simple and complex syllable codas in a range of vocalic environments. Results show that the tongue dorsum shows the least movement in [-ɑɹ-] and [-ɔɹ-] sequences. This dorsal stability sheds light on why [ɑ] and [ɔ] are the only full vowels occurring before codas with /ɹ/ and a non-coronal consonant. English syllable rimes have been analyzed as maximally three timing units in length (Hammond 1999). Long vowels occupy two units, and most coda consonants occupy one unit, rendering rimes with long [ɑ]/[ɔ] followed by [ɹp] or [ɹk] problematic. We hypothesize that the high degree of overlap in the dorsal posture in [ɑɹ] and [ɔɹ] sequences allows their gestures to be partially blended and function like a diphthong that occupies two units in the rime. This study supports a view of maximal constituency in rimes with [ɹ] that takes articulatory overlap into account.