Distinct neural systems recruited when speech production is modulated by different masking sounds

Sophie Meetings, Samuel Evans, Nadine Lavan, Dana Boebinger, Katja Krieger-Redwood, Martin Cooke, Sophie Scott.
Journal of the Acoustical Society of America

When talkers speak in masking sounds, their speech undergoes a variety of acoustic and phoneticchanges. These changes are known collectively as the Lombard effect. Most behavioural researchand neuroimaging research in this area has concentrated on the effect of energetic maskers suchas white noise on Lombard speech. Previous fMRI studies have argued that neural responses tospeaking in noise are driven by the quality of auditory feedback—that is, the audibility of thespeaker’s voice over the masker. However, we also frequently produce speech in the presence ofinformational maskers such as another talker. Here, speakers read sentences over a range ofmaskers varying in their informational and energetic content: speech, rotated speech, speechmodulated noise, and white noise. Subjects also spoke in quiet and listened to the maskers withoutspeaking. When subjects spoke in masking sounds, their vocal intensity increased in line withthe energetic content of the masker. However, the opposite pattern was found neurally. In thesuperior temporal gyrus, activation was most strongly associated with increases in informational,rather than energetic, masking. This suggests that the neural activations associated with speakingin noise are more complex than a simple feedback response.