Project Summary Voice disorders are common, affecting up to 9% of the U.S. population at any given time, and the majority of patients referred to multidisciplinary voice clinics have hyperfunctional voice disorders (HVDs; e.g., vocal fold nodules and muscle tension dysphonia). Clinically, HVDs are characterized by vocal fatigue, dysphonia, and dysregulated muscle activation during voicing. Yet, relatively little is understood about the pathophysiology underlying these signs and symptoms. Elucidating the mechanisms that cause and sustain HVDs is necessary to guide impactful treatment research. Recent studies have identified auditory-motor impairments, including atypical auditory discrimination of voice fundamental frequency (fo) and atypical adaptive vocal learning in response to fo auditory feedback perturbations, in a subset of individuals with HVDs. People with HVDs display atypical voicing across multiple parameters of voice, such as intensity and voice quality, in addition to fo. It is possible that these behaviors relate to a broad auditory-motor impairment for vocal sensorimotor control. Thus, the proposed studies will address the specificity of auditory-motor impairment in HVDs by examining auditory acuity and adaptive vocal learning across two important parameters for vocal sensorimotor control: fo and intensity. In addition to understanding the extent of auditory-motor impairment in HVDs, determining the relationship between such impairments and the clinical characteristics of these disorders is critical to guide clinical research. To date, a direct relationship between auditory-motor impairment and dysregulated muscle activation during voicing, a hallmark of HVDs, has not been established. Co-contraction of opposing perilaryngeal muscles occurs when speakers increase their vocal effort, and is thought to occur during voicing in HVDs. In studies of reaching movements, co-contraction occurs in the limbs in response to feedback perturbations in order to stabilize movements, and decreases as participants adapt to the perturbations. Crucially, studies of limb sensorimotor control also suggest that worse sensory acuity reduces adaptation. Thus, we propose that perilaryngeal co-contraction may occur in response to auditory feedback perturbations in order to stabilize the larynx, and will decrease with adaptive vocal learning. Furthermore, impaired auditory acuity in some speakers with HVDs may be associated with both atypical adaptive vocal learning and persistent perilaryngeal co- contraction compared to speakers without HVDs. Therefore, Aim 1 will compare adaptive vocal learning and perilaryngeal co-contraction in response to perturbations of fo and intensity of auditory feedback in individuals with (n = 26) and without (n = 26) HVDs. Aim 2 will evaluate the prevalence of atypical auditory acuity for vocal fo and intensity in the same groups of speakers. In Aim 3, relationships among auditory acuity, adaptive vocal learning, and perilaryngea...