Which brain regions may help us understand speech masked by noise?

Details

In everyday conversation, people can often understand words masked by background noise as though the missing sounds were still audible. This phenomenon is called phonemic restoration. Because little is known about its neural mechanisms in speech comprehension, researchers aimed to identify them using magnetoencephalography (MEG).

Twelve healthy male volunteers with normal hearing participated. With their eyes closed, they were asked to listen carefully to and understand recorded Japanese stories played either forward or in reverse. Several syllables of the spoken words were replaced with 300-ms white-noise stimuli, with intervals of 1.6–20.3 seconds between stimuli. The researchers used time-frequency analyses to compare MEG responses to the white noise in the forward and reverse conditions.

Compared with the reverse condition, the forward condition showed a continuous increase in 3–5 Hz band power in the left inferior frontal gyrus, in Brodmann areas (BAs) 45, 46 and 47. White-noise stimuli also produced decreases in 18–22 Hz band power in the left transverse temporal gyrus (BA 42) and superior temporal gyrus (BA 22). The results suggest that these left frontal and temporal regions are involved in phonemic restoration for speech comprehension. The researchers said the findings may help clarify the neural mechanisms and contribute to developing innovative treatments for people with impaired speech comprehension, particularly in noisy environments.