Units of sound representation and temporal integration: a mismatch negativity study.

Two acoustic events occurring successively within 200 ms are processed as a single event when the first event predicts the occurrence of the second, but are processed as two separate events when the two events can also occur independently of each other and thus the second event provides new information. However, if the two events are carried by the same stimulus, they are always processed as a single event. This was shown by studies using the mismatch negativity (MMN) event-related potential (ERP). The current study was aimed at investigating the acoustic parameters that determine the integration of successive events within the putative temporal window of integration (TWI). The results demonstrate that temporal grouping (achieved here by presenting sounds in pairs) of the acoustic events within the TWI creates strong unitization, which is not broken up by higher level contingencies of the sound sequence, such as the predictability of the second successive event.