engleski

Role of the N100 to model temporal asymmetry in the auditory system

Communications sounds are typically asymmetric in time and human listeners are highly sensitive to temporal asymmetry. Although models based on multi-channel auto-correlograms and all-order histograms of auditory nerve excitations can be used to predict pitch and musical timbre, these computations fail to model temporal asymmetry. In contrast “strobed” temporal integration of the auditory nerve excitation results in a similar representation but accounts for the asymmetry as reflected by the perceived tonal component sinusoidal carriers [1]. We employed auditory evoked fields (AEF) elicited by ramped and damped sinusoids to investigate the representation of temporal asymmetry in the auditory cortex and the relation to computer simulations. According to [1] ramped and damped sinusoids were constructed by applying different exponential decay times to 50 ms segments of 1000 Hz sinusoids. In the first experiment identical segments were concatenated to produce continuous sounds. In the second experiment isolated segments were used as transient stimuli. AEF were recorded in 10 subjects who listened passively to the stimuli. In a psychoacoustic task tonality of all sounds was derived using a two-alternative forced choice task (Bradley-Terry-Luce method). Spatio-temporal source analysis was used to fit the P30m and the N100m, respectively. Source waveform morphology of the middle latency responses closely reflected the envelope of the sounds but could not account for the perceived asymmetry. In contrast, the N100m amplitude evoked by the continuous and the transient sounds correlated highly with perceived tonality. Furthermore, the N100m amplitude as well as the tonality closely mirrored the “strobed” temporal integration computations. Thus, the N100m might be used to further investigate the timbre of communication sounds and might serve as an objective tool to further improve auditory perception models.

magnetoencephalography (MEG); human auditory cortex; N100; temporal assymetry

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