Electromagnetic articulography

EMA uses sensor coils placed on the tongue and other parts of the mouth to measure their position and movement over time during speech and swallowing.

Induction coils around the head produce an electromagnetic field that creates, or induces, a current in the sensors in the mouth.

Fluoroscopy and X-ray microbeam allow the investigation of non-contact movements of the mouth like EMA, but expose subjects to ionizing radiation which limits the amount of data that can be collected from a given participant.

The ability to observe the movements of articulators has been of great importance to the study of phonetics in order to understand the way sounds are produced.

Sensor coils placed midsagittally in the mouth produce current as they move through the magnetic field inversely proportional to the cube of the distance from the transmitters.

[3][4] In two-dimensional articulography, transmitter coils are placed in an equilateral triangle along the midsagittal plane at the forehead, chin, and neck.

Some researchers have found that subjects are irritated by sensor coils placed on the tip of the tongue which can lead to disturbed articulation.

[8] It has not been shown that long term exposure to electromagnetic fields is harmful to human health, but it is recommended to avoid subjects who are pregnant or who utilize pacemakers.

[9] The field and frequencies output by electromagnetic articulographs are comparable to those put out by computer terminals with the maximum measured being about 10 μT.

It is considered the gold standard in studies of dysphagia because of its ability to take videos of the entire digestive tract during swallowing events.

Radiation exposure is limited by using computer software to focus narrow X-ray beams, about 6 mm2, on the pellets and track them as they move.