Hierarchical processing of temporal asymmetry in human auditory cortex

Communication sounds are typically asymmetric in time and human listeners are highly sensitive to short-term temporal asymmetry. Nevertheless neurophysiological correlates of perceptual asymmetry remain largely elusive to current ap-proaches. Physiological recordings suggest that perceptual asymmetry is based on multiple scales of temporal integration within the auditory processing hierarchy. To test this hypothesis, we used magneto-encephalographic recordings to perform a model-driven analysis of auditory evoked fields (AEF) elicited by asymmetric sounds characterised by rising or decreasing envelopes (ramped and damped, respectively), using a hierarchical model of pitch perception with top-down modulation. We found a strong correlation between the perceived salience of ramped and damped stimuli and the AEFs, as quantified by the amplitude of the N100m component. Furthermore, the N100m magnitude is closely mirrored by a hierarchical model with stimulus-driven temporal integration windows of auditory nerve activity patterns. This strong correlation of AEFs, perception and modelling suggests that temporal asymmetry is processed in a hierarchical manner where integration windows are top-down modulated.