Human scalp evoked potentials related to the fusion between a sound source and its simulated reflection.

The auditory system needs to fuse the direct wave (lead) from a sound source and its time-delayed reflections (lag) to achieve a single sound image perception. This lead-lag fusion plays crucial roles in auditory processing in reverberant environments. Here, we investigated neural correlates of the lead-lag fusion by tracking human cortical potentials evoked by a break in the correlation (BIC) between the lead and lag when the time delay between the two was 0, 2, or 4 ms. The BIC evoked a scalp potential consisting of an N1 and a P2 component. Both components were modulated by the delay. The effects of the delay on the amplitude of the two components were similar, an increase of the delay resulting in a decrease of the amplitude. In contrast, the delay differently modulated the latency of the two components, an increase of the delay resulting in an increase of the P2 latency but not an increase of the N1 latency. Similar to the P2 latency, the reaction time for subjective detection of the BIC also increased with the delay. These findings suggest that both the N1 and the P2 evoked by the BIC are neural correlates of the lead-lag fusion and that, relative to the N1, the P2 may be more closely related to listeners' perception of the fusion. Our study thus provides a neurophysiological and objective approach for investigating the fusion between the direct sound wave from a sound source and its reflections.