Speech Motor Learning Depends on Relevant Auditory Errors

In the past, researchers have studied the elements of speech and how they work together in the human brain. Auditory feedback, an important aid in speech production, provides information to speakers and allows them to gain an understanding if the prediction of their speech matches their production. The speech motor system uses auditory goals to determine errors in its auditory output during vowel production. We learn from discrepancies between our prediction and auditory feedback. In this study, we examined error assessment processes by systematically manipulating the correspondence between speech motor outputs and their auditory consequences while producing speech. We conducted a study (n = 14 adults) in which participants’ auditory feedback was perturbed to test their learning rate in two conditions. During the trials, participants repeated CVC words and were instructed to prolong the vowel each time. The adaptation trials were used to examine the reliance of auditory feedback and speech prediction by systematically changing the weight of auditory feedback. Participants heard their perturbed feedback through insert earphones in real time. Each speaker’s auditory feedback was perturbed according to task-relevant and task-irrelevant errors. Then, these perturbations were presented to subjects gradually and suddenly in the study. We found that adaptation was less extensive with task-irrelevant errors, adaptation did not saturate significantly in the sudden condition, and adaptation, which was expected to be extensive and faster in the task-relevant condition, was closer to the rate of adaptation in the task-irrelevant perturbation. Though adjustments are necessary, we found an efficient way for speakers to rely on auditory feedback more than their prediction. Furthermore, this research opens the door to future investigations in adaptation in speech and presents implications for clinical purposes (e.g. speech therapy).