Neural responses to repeated noise structure in sounds are invariant to temporal interruptions
The ability to extract meaning from acoustic environments requires sensitivity to repeating sound structure. Yet, how events that repeat are encoded and maintained in the brain and how the brain responds to events that reoccur at later points in time is not well understood. In two electroencephalography experiments, participants listened to a longer, ongoing white-noise sound which comprised shorter, frozen noise snippets that repeated at a regular 2-Hz rate. In several conditions, the snippet repetition discontinued for a brief period after which the noise snippet reoccurred. The experiments aimed to answer whether neural activity becomes entrained by the regular repetition of noise snippets, whether entrained neural activity self-sustains during the discontinuation period, and how the brain responds to a reoccurring noise snippet. Results show that neural activity is entrained by the snippet repetition, but there was no evidence for self-sustained neural activity during the discontinuation period. However, auditory cortex responded with similar magnitude to a noise snippet reoccurring after a brief discontinuation as it responded to a noise snippet for which the snippet repetition had not been discontinued. This response invariance was observed for different onset times of the reoccurring noise snippet relative to the previously established regularity. The results thus demonstrate that the auditory cortex sensitively responds to, and thus maintains a memory trace of, previously learned acoustic noise independent of temporal interruptions.