Time-Functional Information Stored in Auditory Sensory Memory

Auditory defense system in the human brain enables us to detect the deviant sounds of warning coming from the dangerous animals. The mismatch negativity (MMN) reflects this system. MMN can be elicited even by sound omission. The MMN elicitation by the omission, in itself, provides evidence for the memory-based interpretation because no afferent processes could be activated by physical absence. MMN is generated by the comparison process between sound change and the neural trace of the preceding sounds stored in sensory memory. The formation of memory trace is strongly related to the mechanism termed the temporal window of integration (TWI) which integrates the closely presented sounds into single units. MMN to omission has also provided evidence for the presence of TWI function in sensory memory. MMN to omission in repetitive tones was elicited only with SO As shorter than 160 ms. It suggests a temporal correspondence between the duration of the neural sound representations in sensory memory and the TWI of 160-170 ms. We found that the sensitivity for the deviation nonlinearly declined over time within the duration of sensory memory. In schizophrenia, MMNs to all deviants were small and those latencies were late only in the later part of the TWI. The findings imply the presence of the impaired cognitive function.