UCLA Phonetics Lab ELECTROMAGNETIC ARTICULOGRAPHY (EMA)

The Phonetics Lab no longer owns a Carstens system (AG100) for electromagnetic articulography (EMA). However, the material below, compiled mostly by Taehong Cho many years ago, may still be useful to others.

• How it works (Principles)
• Experimental Steps
• STEP 0: Sterilization and Disinfection
• STEP 1: Warming-Up
• STEP 2: Coating Sensors
• STEP 3: Attaching Silk Cloth
• STEP 4: Drying the Plastic Coating
• STEP 5: Positioning the helmet
• STEP 6: Placing the sensors
• A. Calibration Procedures
• B. Materials for Attachment
• C. Attachment Procedures
• STEP 7: Recording reference points for data rotation (new)
• STEP 8: Recording data
• STEP 9: Removing the pellets and the helmet
• STEP 10: Cleaning-Up at the end of session.
• Where to attach the sensor coils
• Processing data [using Tailor] 
• Restoring 12 bit acoustic data [using Multi-CV] 
• Analyzing the data
• Important Tips and Reminders


Links to:
 

• UCLA Homemade Manual
• Carstens System
• Mark Hasegawa-Johnson's report on the Electromagnetic Exposure Safety (later published as "Electromagnetic exposure safety of the Carstens Articulograph AG100", J. Acoust. Soc. Am. 104:2529-2532, 1998)
• Go Back to Phonetics Lab

Please note:  Development of this site was supported by grants from the UCLA Academic Senate Committee on Research, and NSF grants SBR-0001716 and IIS-9996088, for which we are grateful.  However, the information found in this website is based upon our own experience and tips from other people.  It is possible that this website contains inappropriate or misleading information, re later brands/models of EMA and especially re software, for which funders should not be blamed!

 HOW IT WORKS (From the Carstens Website)

Each of the three transmitters fixed on the helmet produces an alternating magnetic field at different frequencies. The positions of the transmitters form an equilateral triangle whose sides limit the measurement plane of the Articulograph AG100. 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 three transmitters. It is then possible to calculate the XY coordinates and measure, store and display the positions of the 5 (up to 15) sensors.
 
• UCLA Homemade manual for more details.
• Mark Hasegawa-Johnson's report on the Electromagnetic Exposure Safety of the Carstens Articulograph AG100
[Back to Top]

EXPERIMENTAL STEPS

STEP 0: Sterilization and Disinfection

Sterilize and disinfect materials (sensor coils and tweezers) by using Cavicide (can be bought from Amazon). Immerse sensors and tweezers following instructions for STERILIZATION

Less than sterilization is possible, but not usually used here: immersion in glutaraldehyde for a minimum of 20 minutes for HIGH LEVEL DISINFECTION; immersion in ethyl alcohol (75 ~90%) for 20 minutes followed by wiping with Povidone-Iodine can be used for disinfection only (not for sterilization).   

---

• Relevant Definitions (source: Classes Of Disinfectants And Their Uses)
• Antiseptic: An agent that can be used to reduce the microbial population found on skin.
• Disinfectant: An agent that will destroy many of the disease-causing microorganisms present on the surface of an inanimateobject.
• Sterilant: An agent that destroys all microbial organisms including heat-resistant bacterial spores. Sterilization can be achieved by boiling, autoclaving or exposure to toxic chemicals.  Solutions that contain chlorine or glutaraldehyde are frequently used as chemical sterilants.
 
[Back to Top]

---

STEP 1:  Warming-Up

The system must be turned on at least two hours before the actual experiment, in order to allow the coils to warm up and reach a stable temperature. Once the computer and the EMA system are on, it is necessary to start the Art program for the warm-up procedure to begin (after Art starts, you can exit the program and use the computer for other purposes). See the Carstens website and the UCLA homemade manual for details on Art.

---

STEP 2:  Coating Sensors

Dip the sensors into Plasty-Late (modelers plastic)  to coat them. This step protects the sensors by facilitating adhesive removal after the session and also helps keep them clean. (It is also fine to dip the wire about 1-3 inches into Plasty-Late). The solution is milky when wet but transparent when dry.

---

 

---

STEP 3: Attaching Silk Cloth

(Optional but Recommended) Attach the sensors to small circles or squares of silk cloth right after dipping them in the plastic coating (so the cloth sticks to the sensor). (See Figure (3) below.)  As can be seen in Figure (4),  the cloth expands the surface of the sensor coil that is attached to the tongue and consequently helps preventing the sensors from falling off. This step is only recommended for coils that will be attached to the tongue.

---

STEP 4: Drying the Plastic Coating

It is important to leave the plastic coating to dry for at least 2 hours (the longer the better - as a general rule, we leave the coating dry for one night), at which point the sensors can be calibrated in the magnetic field.  Insufficient drying may cause the coating to be broken more easily, which results in the sensors' falling off.

---

 

---

[Back to Top]

STEP 5: Positioning the helmet

The helmet which generates the field is positioned around the subject's head. Since the helmet is rather heavy, it is suspended from a pulley, in order to alleviate some of the weight.

• We have found that by placing the sensors before putting on the helmet, 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.

• However, a drawback may be that one cannot check if the attached sensor coils are correctly detected in the magnetic field during the attachment session.

• Experienced experimenters may find it more efficient to place the sensors before putting on the helmet, especially when the speech material to be recorded is relatively long.  In such a case, examine carefully whether sensors responds to the system constantly as the lead at the coil base out  is gently twisted around.  This is usually done when sensors are calibrated.

[Back to Top]

STEP 6: Placing the sensors

A. Calibration Procedures

    It is essential to perform a calibration of the system before each experiment.
    Please go to our UCLA Homemade EMA Manual for detailed Calibration Procedures.

---

B. Materials for Attachment

In order to place the sensors, several materials should be prepared.

 

•  Adhesives
•  For internal use (inside the mouth): dental adhesive, formerly Cyano-Veneer® Fast , now a PeriAcryl cyanoacrylate dental formulation tissue adhesive from Gluestitch.com, but we note that Haskins uses Ketac-Bond cavity liner 
• For external use (outside the mouth): skin adhesive, formerly Skin-Bond® by Smith and Nephew, now a liquid bonding cement ordered from Amazon, but we note that Haskins uses Iso-dent from Ellman International      
• Reversal Tweezers
• The reversal tweezers help in holding the sensor coil with precision and not dropping it.  Reversal tweezers can be ordered from a surgical supplies store.
• Gloves
• Medical Tape
• To affix sensor coils to the face and lips (instead of using Skin-bond).
• To tape the leads to the cheek so that they don't get pulled off.
• Gauze and/or Cotton Pad
• To wipe the tongue in order to dry the tongue surface (we found that using cotton pads is better than using gauze).
• Cosmetic pencil (not in figure)
• To put a dot on the point of the tongue to which the sensor coil is attached.
• Hair-Dryer (not in figure)
• To dry the tongue tissue thoroughly. It is important to use a dryer with a "cold lock" option.
• Tissues (not in figure)

---

[Back to Top]

C. Attachment Procedures

It is recommended that two experimenters conduct the attachment session.
 
1. Hold the sensor coils (Reversal Tweezers) -- Experimenter 1.
2. Thoroughly dry the area to which the sensor coil is to be attached with a cotton gauze pad. (Cotton Gauze Pad) -- Experimenter 2
3. (Optional) Put a dot on the spot of the tongue to which the sensor coil is to be attached. (Cosmetic Pencil) -- Experimenter 1
4. Apply a drop of the internal adhesive to the surface of the silk cloth (on  the sensor coil) (Cyano-Veneer) -- Experimenter 2
5. Wipe out the surface of the tongue quickly (New Cotton Gauze Pad) -- Experimenter 1
6. Place the coil -- Experimenter 1   [Steps 4-6 must be done almost simultaneously]
7. Release the tweezers immediately. (It is important to release the tweezers immediately after the attachment in order to prevent the tweezers tips from sticking to the coil.) -- Experimenter 1
8. Dry the surface around the coil using a hair-dryer for about two minutes -- Experimenter 2. Experimenter 2 must start drying the subject's tongue (using cold air) from the moment in which the coil is attached. This procedure helps the sensor coils to stick to the surface of the tongue longer.  (For a short data collection session, this step can be omitted.)
9. While the tongue is being dried, press the top of the coil with the tip of the tweezers for at least 30  seconds, starting immediately after the coil is attached (remove the tweezers periodically, to make sure that they did not stick to the coil). Of course, during this and the previous step the subject's tongue should remain in a position in which the coil is accessible/visible. -- Experimenter 1
10. Stabilize the fine lead wire with a strip of medical tape on the cheek. (These wires must be led out via the corner of the mouth and across the cheek).

• While their tongue is being dried, subjects tend to drool. Thus, it is a good idea to provide them with tissues that they can use to dry the lower half of their face. Also, it is a good idea to keep a towel on the subject's lap during the whole attachment procedure, to protect the subject's clothes from glue spillings.
• The procedure described above is recommended when attaching sensors to the tongue as well as the lower gum.. If sensors have to be attached to the upper gum, there is typically no need to dry the area with the hair-dryer, even if it is still a good idea to wipe the area with a cotton pad and to press the coil with the tweezers and/or a finger for about 30 seconds. We found that it is very useful if subjects are willing to hold their lips while we are attaching coils to the gum or teeth.  If sensors are attached outside the mouth, it is sufficient to attach them using the skin adhesive, and there is no need to dry the surface with the cotton pads and the dryer, nor to press the coils.
• Time to take for attaching sensor coils: From experience, we know that attaching 5 sensors in their positions in the mouth and on the face typically takes  about 15 minutes, 10 sensors take about 30 minutes. Subjects may then require additional time to get used to speaking with the sensors..
• Time the coils will typically stay attached: Sensor coils attached in the way described above can stay attached for as long as three hours, if the subject is not constantly speaking. In a data collection session, it is reasonable to expect carefully attached sensors to stay attached for at least one hour.
• Figures: "Placing a sensor coil" & "Yes, I am ready!"

 

 [Back to Top]

STEP 7.  Recording Reference Points for Data Rotation

• The co-ordinate system for the EMA data is determined by the helmet position during the data acquisition.  Therefore, the x (horizontal) and y (vertical) values of sensor pellets, for example, placed on the tongue do not directly map to the tongue's horizontal and vertical movements.
• Thus, the EMA data requires rotation to the occlusal plane.
• The occlusal plane (sometimes called "bite plane") is generally determined using a bite plate on which two sensor pellets are fixed.  The figure below is a bite plate we generally use here.
• Figure: Bite Plate.
- The width of the bite plate is about 4.5 cm for an average size woman and 5.5 cm for an average size man (exactly the same size as a credit card).
- A new bite plate is made for each subject by laminating a relatively thick paper (at Kinko's, Copy Service, for $1.00-2.00 each).
• Procedure
- First, fix two pellets as you see in the figure
- Insert it into the subject's mouth
- Record for a few seconds with the bite plate in the subject's mouth
(See below how to use this reference for rotation)

STEP 8.  Recording Data

• The data is recorded in small segments (called "sweeps"), typically of 1 to 4 sentences (each sweep can hold up to 30 seconds of recorded data). The sweeps contain position information about the sensors, as well as an acoustic record of the session. (The quality of the acoustic recording is poor, so a separate audio recording is necessary if any acoustic analysis must be performed.)
• Unfortunately, if acoustic data are collected, each sweep is played back as Art saves it. Thus, data collection takes approximately twice as long as one might think!
• It is a good idea to design experiments so they can be stopped part way through and still have useful data, just in case that sensors accidentally fall off earlier than expected.


      See UCLA Homemade Manual for Performing an Actual Measurement Sweep.

[Back to Top]

STEP 9. Removing the helmet and the pellets

 
• While it is more practical to remove the pellets before the helmet, if the subject looks very tired, it is a good idea to first take the helmet off, and to remove the pellets afterwards.
• We do not use special tools to remove the pellets. Subjects typically find it easier to take off the tongue pellets by sliding their tongue under the upper teeth.

STEP 10.  Cleaning-Up

• Soak the sensor coils and the coated wires in the adhesive remover solution, "Uni-Solve" by Smith and Nephew (1-800-876-1261), until they look clean (often, we have to leave the coils in the solution overnight).
• Carefully remove the rubber coating from the sensor coils and and wires.
• Sterilize and Disinfect the coils (STEP 0).
• IMPORTANT: We frequently lose (expensive) sensor coils due to broken leads at the coil base. This damage comes primarily  from hasty and careless cleaning-up at the end of the session.  Soaking sensor coils in Uni-Solve for a while & extremely careful handling can reduce the damage to the coil base.

Where to Attach Sensor Coils

 

• a. tongue dorsum: approximately 4 cm from tip of tongue, depending on speaker.  The exact position may be determined by static palatography if precision is needed
• b. midpoint of tongue body
• c. tongue tip: approximately 1 cm from tip of tongue
• d. base of low front incisors: to measure jaw movement
• e. lower lip
• f. upper lip
• r. bridge of the nose (as a reference point)
• r. base of upper front incisors (as a reference point)

• Order of coil attachment: Attach coils from the backmost point inside the mouth, approximately from (a) - (f) (however, it is sometimes easier to attach tongue coils starting from the frontmost one); attach reference points last.
• Some subjects prefer to have the coils d. and r. attached to their teeth (approximately on the ridge between the front incisors), and this is necessary for subjects whose gums easily bleed. However, we often attach the coils to the gum, instead (under the lower front incisors; over the upper front incisors). An advantage of gum attachment is that the lips hold the coils in place. Furthermore, after coil removal, the glue tends to go away earlier from the gum than from the teeth.

[Back to Top]

Processing the data [using Tailor]

• Before using Emalyse to measure position data, several processing steps are needed using the Tailor software.  Please refer to Tailor manual.
1. Filtering (see also the Tailor manual p.7-9)
• Filter_40: this filter is the strongest for smoothing.  It is recommended by Carstens to use this filter for fixed reference points.  The cut-off frequency is at sample frequency/25.  At a sample frequency of 1000 Hz, the cut-off frequency if 40 Hz and the filter offers a 60 dB depression at 90 Hz.  (The cut-off frequency, therefore, depends on the sample frequency.) USE THIS FOR SENSORS AT TWO REFERENCE POINTS (UPPER GUMLINE, NOSE BRIDGE.)
• Filter_100: The cut-off frequency is at sample frequency/10. As a sample frequency of 1000 Hz, the cut-off frequency is 100 Hz and the filter offers a 60 dB depression at 150 Hz. USE THIS FOR MOST SENSORS.
• Filter_160: This filter is for weak smoothing of movement signals.  The cut-off frequency is at sample frequency/6.25. At a sample frequency of 1000 Hz, the cut-off frequency is 160 Hz and the filter offers a 60 dB depression at 210 Hz.
2. Dynamic correction for head movement
• The dynamic correction procedure modifies the co-ordinate system individually, sample by sample, in such a way that both reference sensors stay still.  This step eliminates the errors caused by helmet movement during the recording session. (from p.9 in the Tailor manual)
3. Rotation to the occlusal plane
• First, determine carefully by what angle the data needs rotating.  This can be determined by using x'(distance between two x points) and y' (distance between two y points) values of two points on the bite plate. The angle is the arctangent of y'/x' (theta = tan^-1 y'/x').
• Enter the angle determined in the box provided. This process rotate the entire data.

Restoring 12 bit acoustic data [using Multi-CV]

• The speech processors generate, store and process the acoustic data in the compressed 4-bit ADPCM format. Emalyse can read only this compressed format.  Thus, the acoustic data in Emalyse should not be used for any serious acoustic measurement.
• However, the compressed acoustic data can be 'uncompressed' to the 12-BIT PCM format which can be used for serious acoustic measures.  Multi-CV allows this conversion.  First, open a data file in the Multi-CV, mark "sound-wav" function, choose the sweep numbers you are interested in. Let it run. The 12 bit acoustic data (.wav) will be stored in the folder "Convert" in the same directory in which your original data are.

Analyzing the data

• we use the EMALYSE software to measure position data.

• 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?"):

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

 Important Tips & Reminders

1. Attach a small circle/square of silk cloth to the sensor coils right after dipping into "Plasty-late"
2. Thoroughly dry the rubber coating (at least 3 hours) before the experiment starts
3. Pay extremely careful attention to drying the surface of the tongue right before placing a sensor coil. Make sure that the surface is wiped twice. Drying the tongue is so important that other institutes use a "saliva vacuum" like the one dentists use.
4. Gently press the sensor coil against the tongue surface with the tips of the tweezers or a finger for about 30 seconds.
5. During the placement procedure, the second experimenter should dry the subject's tongue with a hair-dryer. This helps the glue drying thoroughly.  In other institutes, a tiny nozzled air blower like the ones used by dentists is used to blow air on the glued sensor coils.
6. Reversal Tweezers makes the coil placement easier, preventing the sensor coils from slipping out.
7. It's always a good idea to have two experimenters performing the coil placement. One experimenter holds the coil, quickly wipes the tongue, places the sensor coil, and gently presses the sensor coil against the tongue. The second experimenter wipes the tongue before the placement procedure starts, puts a drop of glue on the silk-surfaced coil, blows the hair-dryer (with cool air).
8. While their tongue is being dried, subjects tend to drool. Thus, it is a good idea to provide them with tissues that they can use to dry the lower half of their face. Also, it is a good idea to keep a towel on the subject's lap during the whole attachment procedure, to protect the subject's clothes from glue spillings.
9. When attaching the coils to the base of incisors, make sure that the front teeth do not have fillers or any synthetic material that might be destroyed by the glue.
10. It is a good idea to design experiments so they can be stopped part way through and still have useful data, just in case sensors accidentally detach earlier than expected.
11. Dip the used sensor coils into Uni-Solve at least for several hours so that we can reduce the damage while peeling off the rubber coating. We typically soak them for a day or two to minimize the damage.  It is also suggested (Tips and Tricks at Carstens) that the loss of receiver coils due to broken leads at the coil base can be reduced by occasionally dipping the stripped-down coils in Cyano-Veneer up as far as the sleeve of the coils.

 

Last updated: content 02/18/00 (by Taehong Cho), links Oct. 2017 (Pat Keating)