Evaluation of a Wireless Tongue Tracking System on the Identification of Phoneme Landmarks

Objective: Evaluate the accuracy of a tongue tracking system based on the localization of a permanent magnet to generate a baseline of phoneme landmarks. The positional variability of the landmarks provides an indirect measure of the tracking errors to estimate the position of a small tracer attached on the tongue. The creation of a subject-independent (universal) baseline was also attempted for the first time. Method: 2,500 tongue trajectories were collected from 10 subjects tasked to utter 10 repetitions of 25 phonemes. A landmark was identified from each tongue trajectory, and tracking errors were calculated by comparing the distance of each repetition landmark to a final landmark set as their mean position. Results: In the subject-dependent baseline, the tracking errors were found to be generally consistent across all phonemes, and subjects, with less than 25% of the errors reported to be greater than 5.8 mm (median: 3.9 mm). However, the inter-subject variability showed that current limitations of our system resulted in appreciable errors (median: 55 mm, Q3: 65 mm). Conclusion: The tracking errors reported in the subject-dependent case demonstrated the potential of our system to generate a baseline of phoneme landmarks. We have identified areas of improvement that will reduce the gap between the subject-dependent, and universal baseline, while lowering tracking errors to be comparable to the gold standard. Significance: Creating a baseline of phoneme landmarks can help people affected by speech sound disorders to improve their intelligibility using visual feedback that guides their tongue placement to the proper position.