Advances in the use of alternating magnetic fields to track articulatory movements

Abstract

We have reported on a prototype device for simultaneous tracking of movements of several points on articulatory structures inside and outside the vocal tract [J. S. Perkell and D. Oka, J. Acoust, Soc. Am. Suppl. I 67, S92 (1980)]. Alternating magnetic fields are generated by two fixed transmitter coils. The midsaggital plane locations of small, movable probe coils (transducers) can be computed from the amplitude of signals induced in the transducers, as long as the axes of the transmitter and probe coils are parallel to one another. Initial recordings of movements of transducers mounted on the tongue suggested that some tongue movements caused enough tilting of the transducers to produce significantly inaccurate location measurements. In conjunction with Piconics, Inc. (Tyngsboro, MA), we have devised a miniature biaxial transducer containing two orthogonally oriented sets of windings. Signals from the two windings are used to compute separation between a transmitter coil and the transducer, independent of the amount of tilt of the transducer with respect to the transmitter. Bench tests of the transducer indicate that the system may be used to track articulatory movements with an accuracy better than 0.5 mm regardless of transducer tilt. [Research supported by N.I.H. Grant No. NSO4332.]