EMA - Electromagnetic Articulography
General Introduction
Reliable research on speech and speech disorders best encompasses an analysis
of both the acoustics and the mechanics of speech. The study of the mechanics
of speech has been problematic because movements within the mouth are difficult
to measure and visualise. Essential information for speech therapists, scientists
and medical doctors such as the order of and time lapse between mouth movement
and sound or the exact position of the tongue have been next to impossible
to collect. Researchers have not been able to track movements within the
oral cavity and have not received measurement data ready for evaluation.
Scientists in the fields of dentistry, neurology, neuro-physiology, and
phonetics have been searching for less work intensive, more useful technology
for articulographic studies.
The electromagnetic articulography provides a solution to these problems
in speech mechanics research. The movement itself is measured, graphed
and saved. The connection between the fields of acoustic and mechanical
speech research are made. Now with the new AG500 sensor placement is allowed
at all positions and in all orientations within 300 mm spherical measurement
area.
The Articulograph AG500 can be used in research and for clinical application.
The unit allows measuring with high timing resolution. It is comprised of
a plastic case, small connector coils that are positioned on and in the
subjects mouth, and a electronic that can be connected to the Windows Computer.
Together with the accompanying software, the procedure from set up to measurement
to data analysis is clear and allows the user to access otherwise unavailable
information about tongue, mouth, palate, and jaw movement.
Operation principles
Each of the six transmitters fixed on the case produces an alternating magnetic
field at different frequencies. The alternating magnetic field induces an
alternating current in the sensors, much like in a transformer, and allows
one to obtain the distances of each sensor from the six transmitters. It
is then possible to calculate the XYZ co-ordinates as well as two angles
and measure, store and display the positions of the sensors.
History
The 2-dimensional Electromagnetic Articulography was initially developed
at the Medical School of the University of Göttingen, starting in 1982.
The earliest version of an EMA procedure was developed in 1974 by Sonoda
in which a permanent magnet was fastened to the tongue, with a second magnet
being located outside of the mouth. In this procedure only the position
of the magnet in the mouth could be determined. Hixon (1971) and van der
Giet (1977) used alternating fields and various transmitter signals, enabling
one to measure several points within the mouth. This idea was developed
further in 1980 by Perkell who developed a unit with two transmitter coils
and miniature sensors. In 1983 Schönle was able to register 4 different
points within the mouth with a similar procedure.
1988 Carstens Medizinelektronik developed the first commercial Articulograph, the AG100.
Since 1995 Carstens Medizinelektronik and the Phonetics department of
the University of Munich under the direction of Prof. Hans G. Tillmann and
with the support of NTT Japan, have been developing the new 5-dimensional
Articulograph AG500.