Evidence that the Lombard effect is frequency-specific in humans

Recent perspectives suggest that the Lombard effect is an increase in the suprasegmental speech parameters of vocal intensity, duration, and fundamental frequency in the presence of noise. It has been viewed as a non-specific response to ambient noise, but this assumption has not been thoroughly tested. Two experiments using healthy adults measured intensity, duration, and F0 changes in broadband (0.2-20 kHz) and notched noise (0.05-4 kHz removed) during a picture naming task. The pilot experiment showed that broadband noise containing speech-similar frequencies significantly increased intensity, duration, and F0 while notched noise, which removed the majority of speech-similar frequencies, had no effect. The main experiment added bandpass noise (0.05-4.0 kHz) which contained a major portion of speech-similar frequencies and was the mirror image of the notched noise. Broadband and notched noise results were replicated. Bandpass noise increased intensity and duration, but to a lesser degree than did broadband noise, and had no effect on F0. Findings show that the Lombard effect is sensitive to frequencies vital for speech and is not a general response to any competing sound in the environment. Implications for suprasegmental control of speech are discussed. (C) 2013 Acoustical Society of America.