Auditory–Motor Mechanisms of the Lombard Effect

PURPOSE: The Lombard effect, a speaker's increase of vocal intensity in the presence of noise, is a common phenomenon. However, its underlying auditory mechanisms are unclear. METHOD: Participants produced speech before (baseline), during, and after exposure to systematically varied levels of speech-shaped noise. Lombard responses (i.e., elevated vocal intensity from baseline) were measured in an ecologically valid task (noise presented prior to voicing onset; Experiment 1) and in a task modeled after vocal motor learning paradigms (noise triggered by voice onset; Experiment 2). Loudness discrimination was assessed in the participants in Experiment 1. RESULTS: Compared to baseline, vocal intensity was elevated during noise in both experiments, suggesting contributions of both feedback and feedforward mechanisms to Lombard responses. Vocal intensity during noise was greater when noise was presented prior to voicing onset, as compared to when noise was triggered by voice onset. Intensity was decreased from baseline after noise exposure in Experiment 1 but not Experiment 2. Loudness discrimination thresholds did not explain the variance in Lombard responses. CONCLUSIONS: Lombard responses are driven by both auditory feedback and the updating of feedforward mechanisms. Acuity did not explain the variance in Lombard responses, motivating future studies to investigate other contributing factors. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.32408403.