Integrating Ambulatory Biofeedback Based on Harmonic Level Differences Into Vocal Hyperfunction Treatment: Two Case Studies.

OBJECTIVES: Ambulatory biofeedback has been associated with improved generalization of modified pitch or loudness from the clinic into daily life for patients with Vocal Hyperfunction (VH). Pitch and loudness are auditory perceptual constructs readily detected and modified by many patients. They also have close connections to objective acoustic measures like fundamental frequency and sound pressure level. However, these constructs are not directly related to VH's pathophysiology. In contrast, H1-H2-the difference between the first two harmonics-is directly linked to abnormal vocal fold closure dynamics and treatment improvements. But its association with constructs that the patient can perceive-like breathiness, strain, airflow, and resonance-is more nuanced than pitch and loudness. This proof-of-concept study formally tested if ambulatory biofeedback based on H1-H2 can help two patients improve generalization in voice therapy. METHOD: Two patients with VH wore a voice monitor in daily life before starting voice therapy and after three therapy sessions. Biofeedback was turned on in daily life only after the second therapy session. Biofeedback consisted of a 200-ms vibrotactile cue when a H1-H2 threshold was surpassed for 500-ms. RESULTS: Neither patient generalized after session 1. For both patients, ambulatory biofeedback based on H1-H2 was associated with significantly increased generalization after session 2 compared to baseline monitoring (d = 0.8-1.6) and session 1 (d = 1.2-1.7). Only one patient retained his increased generalization when the biofeedback was turned off after session 3 compared to baseline (d = 0.9) and session 1 (d = 1.3). CONCLUSIONS: Ambulatory biofeedback based on H1-H2 improved generalization for both VH patients, however, only one patient retained improvements after turning the biofeedback off. Future work should investigate the efficacy of incorporating H1-H2, and potentially other biomarkers associated with pathophysiology into ambulatory biofeedback for patients with VH.