Non-invasive study on articulation using magnetic resonance imaging movie

Objectives: To explore the application of magnetic resonance imaging (MRI) movie in the evaluation of the relationship among articulators in plosives with reference to their places of articulation.

Methods: Ten adult females were recruited. Custom-made circuitry was connected to a 1.5T MRI apparatus, equipped with a head and neck coil, to enable an external trigger pulse to control the timing of the scanning sequence and to provide an auditory cue for synchronization of the subject's utterance, which was recorded simultaneously using an optical microphone. Each image had a 219-x250-mm field of view (slice thickness: 5mm), and the matrix size was 108x128. The subject repeated vowel-consonant-vowel (VCV) syllables of the bilabial (/apa/) and velar (/aka/) plosives, synchronized to the auditory cue in a modified “waltz” rhythm 36times during 1500ms for each utterance. Several linear and angular were defined to delineate the individual movement of articulators and to determine the temporal relationship among them.

Results: In both situations, velar movement was critical for securing velopharyngeal closure to establish plosives at an identical timing, and there was a significant coherence between velar and mandibular movement. Moreover, there were significant correlations between the timing of velopharyngeal closure and the timing of the first maximum retraction (p=0.02) and protrusion (p=0.00) of the anterior part of the tongue during /apa/. Likewise, there were significant correlations between the timing of velopharyngeal closure and the timing of the first maximum retraction (p=0.03) and protrusion (p=0.00) of the posterior part of the tongue during /aka/.

Conclusion: The results suggest that articulatory movement could be recorded with high spatiotemporal resolution using MRI movie. Further, there seems to be a central and/or reflexive mechanism that controls the spatiotemporal relationship among articulators, and the level of coupling may be associated with the place of articulation.