Cortical activation associated with the unmasking effect of perceived separation on speech perception

Abstract

Spatial separation between the sound images of the target speech and the masker can improve recognition of the target speech, especially when the masker is irrelevant speech. In the present study, functional magnetic resonance imaging (fMRI) was used to investigate the neural basis of the unmasking effect of the perceived spatial separation. Target sentence was presented along with either steady-state speech-spectrum noise or irrelevant 2-talker speech at the signal-to-noise ratio of -8 dB through headphones. Position of the target image and that of the masker image were manipulated separately by modulating the time interval between the left and the right headphones, thus the two images were either co-located or separated. Sparse temporal sampling was used to avoid the influence of scanner noise. The results show that bilateral superior temporal gyrus (STG) activation was larger under the speech-masking condition relative to the noise-masking condition. When the masker is speech but not noise, the target-masker co-location was associated with more activation in left post parietal lobe and bilateral precentral/postcentral gyrus relative to the target-masker separation. The results suggest that more demand of both attention resource and central processing are required when the target speech is perceived as co-located with the speech masker.