Auditory scene analysis and sensory memory: the role of the auditory N100m.

We consider the neural dynamics underlying auditory streaming, the perceptual grouping of transient auditory events, by using neural modeling and magnetoencephalographic (MEG) measurements in humans. We demonstrate that spatial variations in the strength of feedback inhibition leads to differential amplitude modulation (AM) tuning resembling that found in animal models. In our model, neurons respond selectively to stimuli presented at different onset-to-onset interstimulus intervals (ISIs), and their summed activity (corresponding to the MEG signal) exhibits both transient and sustained responses (SRs) at fast ISIs. In MEG measurements utilizing 2-s trains of 50-ms stimuli presented at 0-1950 ms ISIs, we observed the transient N100m and SRs predicted by the model, with a prominent SR emerging for discrete stimuli at ISIs below 200 ms. Our results explain why, at fast stimulus rates, the amplitude of the auditory N100m appears to be strongly attenuated even though auditory cortex continues to respond vigorously to the stimuli. The results suggest that the longer and shorter forms of auditory sensory memory may be reflected in the N100m and the SR, respectively. As the emergence of the SR coincides with the stimuli being perceived as auditory streams, our study suggests that auditory sensory memory as indexed by transient and sustained cortical activity might underlie auditory scene analysis.