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Published on: June 14, 2014
Auditory-Motor Mechanisms of the Lombard Effect
Allison S Aaron1, Manuel Díaz Cádiz1, Sarah Cocroft1
1Department of Speech, Language & Hearing Sciences, Boston University, MA.
Summary
The Lombard effect, where speech intensity increases in noise, involves both auditory feedback and feedforward mechanisms. Loudness perception did not explain these vocal adjustments.
Area of Science:
- Speech production
- Auditory perception
- Acoustic phonetics
Background:
- The Lombard effect, an involuntary increase in vocal intensity in response to background noise, is a well-documented phenomenon.
- Despite its prevalence, the precise auditory mechanisms driving the Lombard effect remain incompletely understood.
Purpose of the Study:
- To investigate the auditory mechanisms underlying the Lombard effect.
- To differentiate the roles of auditory feedback and feedforward control in vocal adjustments to noise.
Main Methods:
- Participants produced speech in quiet (baseline) and during exposure to varying levels of speech-shaped noise.
- Two experimental paradigms were used: noise presented before vocalization (Experiment 1) and noise triggered by voice onset (Experiment 2).
- Loudness discrimination was assessed in Experiment 1.
Main Results:
- Vocal intensity significantly increased during noise exposure compared to baseline in both experiments, indicating contributions from both feedback and feedforward processes.
- Higher vocal intensity was observed when noise preceded vocalization, suggesting a stronger feedforward influence in this condition.
- Vocal intensity decreased below baseline after noise exposure in Experiment 1, but not in Experiment 2.
- Loudness discrimination thresholds did not correlate with the magnitude of Lombard responses.
Conclusions:
- Lombard responses are mediated by a combination of auditory feedback and the adaptation of feedforward motor commands.
- Auditory acuity alone does not account for individual differences in Lombard responses, suggesting other factors are involved.
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