UCLA Phonetics Lab

ELECTROMAGNETIC
ARTICULOGRAPHY




The Phonetics Lab owns a Carstens system (AG100) for electromagnetic articulography (EMA). Currently we have five receiving pellets, which can be placed midsagitally inside the mouth or on the face to measure movements during speech production.

An EMA experiment typically involves the following steps:

1. Warm-up: the system must be turned on about two hours before the actual experiment, in order to allow the coils to warm up and reach a stable temperature.

2. Preparation and calibration of the sensors: the pellets are dipped into modelers plastic to coat them. (This protects the pellets and also helps keep them clean.) The plastic coating takes about 15 minutes to dry, at which point the pellets are calibrated in the magnetic field.

3. Familiarizing the subject with the procedure: once the system is warmed up and calibrated, we are ready for the subject. The equipment is shown to the subject, and the procedure is explained in some detail, since the subject must give informed consent to participate in the experiment.

4. Placing the sensors. The pellets are positioned on the subject as follows: for measurements inside the mouth, the pellets are attached to the tongue with a medical adhesive for internal use. For positions outside, the mouth, we generally use medical tape (i.e., gauze adhesive) to affix pellets to the face and lips. Typical positions might include a subset of the following:

If it is necessary to make a palate trace first, then the last sensor (probably the reference) is not positioned until after the helmet is in place (step 5)

5. Positioning the helmet: once the sensors are in place, the helmet which generates the field is positioned around the subject's head. Since the helmet is rather heavy, it is suspended from a hook above, in order to alleviate some of the weight. We have found that by placing the sensors before putting on the helment, the subject has some time to adjust to having the sensors attached, and also does not have to sit so long with the heavy helmet on.



6. Recording the data: the data is recorded in small segments (called "sweeps"), typically of 1 to 4 sentences. The sweeps contain position information about the sensors, as well as an acoustic record of the session. (The quality of the acoustic recording tends not to be very good, so a separate audio recording is necessary if there will be any acoustic analysis performed.) Unfortunately, during the recording, the software must play back the entire sweep as it saves it, so this makes data collection take approximately twice as long as one might think! It is a good idea to design experiments so they can be stopped partway through and still have useful data. We try to aim for about half an hour in the machine, but some experiments have been considerably longer.

7. Analyzing the data: we use the EMALYSE software to measure position data. We also have copies of other Carstens software packages, such as the TAILOR, MULTI-CV, and POINTS programs, but so far we have not used these very heavily.
Here is an example display from the Emalyse program, showing two Croatian sentences (Kuda Bibi pada, "Where does Bibi fall?" and Kuda Mimi pada, "Where does Mimi fall?"):

 
1. Acoustic display
2. Y Position (i.e., height)
of two sensors (blue = tongue dorsum, green = lower lip)
3. Velocity of the same two sensors (i.e., the first derivative of the curves in the middle panel)

*** An animation of the articulators in motion, created from EMA data, is also available on the Demos and Illustrations page.



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