Assessing the position tracking reliability of Carstens' AG500 and AG501 electromagnetic articulographs during constrained movements and speech tasks

The goal of this study is to qualitatively and quantitatively assess the reliability of the AG501 Electromagnetic Articulograph (Carstens Medizinelektronik GmbH) and to compare it with the previous model, the AG500, which is still widely used in the 3D recording of articulatory movements. To explore and test the spatial accuracy of the articulographs in various areas of the recording volume, controlled sensor positions at fixed locations and along circular trajectories as well as movements of articulators of the speaker's vocal tract during speech production tasks were tracked and analysed. It is well known that the AG500 trajectories are affected by perturbations which: (i) depend on the position of the sensors/subject within the recording volume and (ii) randomly occur along repetitions of the same sound in the same recording area. This study has shown that these issues do not affect the newer AG501, which not only performs according to the manufacturer's claim of 0.3 mm dynamical accuracy within a 20-cm-wide spherical region inside the recording volume, but also performs well outside. Furthermore, while the AG500 shows perturbed trajectories in some instances, the AG501 consistently shows accurate results in reproducing the displacements of consonantal and vocalic gestures for the tested speech tasks. Our findings reveal that the AG501 is more stable and significantly more accurate than the previous model, the AG500, which, in turn, performs reasonably well only in specific limited conditions.