A Comparative Study of the Precision of Carstens and Northern Digital Instruments Electromagnetic Articulographs.

Purpose: This study compares the precision of the electromagnetic articulographs used in speech research: Northern Digital Instruments' Wave and Carstens' AG200, AG500, and AG501 systems.

Method: The fluctuation of distances between 3 pairs of sensors attached to a manually rotated device that can position them inside the measurement volumes was determined. For each device, 2 precision estimates made on the basis of the 95% quantile range of these distances (QR95) were defined: The local QR95 was computed for bins around specific rotation angles, and the global QR95 was computed for all angles pooled.

Results: For all devices, although the local precision lies around 0.1 cm, the global precision is much more worrisome, ranging from 0.03 cm to 2.18 cm, and displays large variations as a function of the position of the sensors in the measurement volume. No influence of the rotational speed was found. The AG501 produced-by far-the lowest errors, in particular concerning the global precision.

Conclusions: The local precision can be considered suitable for speech articulatory measurements, but the variations of the global precision need to be taken into account by the knowledge of the spatial distribution of errors. A guideline for good practice in EMA recording is proposed for each system.