Muscle tension dysphonia as a disorder of motor learning

Abstract

Background: Adaptive learning has been demonstrated in many areas of motor learning. In speech, adaptive responses to auditory perturbation of fundamental frequency, formant frequencies and centroid frequencies of fricatives have been demonstrated. This dissertation presents the hypothesis that the motor changes observed in muscle tension dysphonia may be due to adaptive learning. To begin to test this hypothesis, an experiment was designed to look for evidence of an adaptive learning response to imposed auditory perturbation of voice quality. Methods: 16 participants repeated the syllable /ha/ while listening to noise under a number of experimental conditions. The training condition presented a re-synthesized recording of the participants own voices, which had an artificially increased noise-toharmonic ratio intended to simulate breathiness. A control condition presented speech babble at the same intensity. Catch trials in which the noise was turned off were included to test for evidence of motor learning, and trials where the participants repeated /he/ were included to test for evidence of generalization to untrained stimuli. H1-H2, a measure of spectral slant, was the dependent measure. A second experiment compared participants’ performance on a task of auditory perception of breathiness to their response to the auditory perturbation. Results: 12 of 16 participants showed statistically different values of H1-H2 between the training and control conditions. As none of the group differences between conditions were significant, this experiment was not able to demonstrate adaptive learning. There was no relationship between performance on the auditory perception task and performance on the adaptive learning task. Conclusions: Given the large body of evidence supporting the concept of adaptive learning in many domains of motor behavior, it is unlikely that behaviors that control voice quality are not subject to adaptive learning. Limitations of the experiment are discussed.