engleski

An Integrated Magnetoencephalographic and Functional Magnetic Resonance Imaging Study On Temporal Asymmetry Processing in the Human Auditory Cortex

Temporal asymmetry is a fundamental property of speech and music. When a "damped" exponential is used to modulate a sinusoid, it reduces the sound quality typically associated with the carrier. When the modulator is reversed in time, producing a "ramped" sound, the sound quality of the carrier is more salient. Magnetoencephalography was used in conjunction with functional magnetic resonance imaging (fMRI) to localize and characterize cortical sources evoked by temporally asymmetric sounds. Additionally, the relation between neurophysiological and psychometric data was explored. We show that the relationship between stimulus perception and neuromagnetic responses are observed in the N100m component of auditory evoked magnetic fields. In response to ramped and damped sinusoids N100m peak amplitudes increase with the stimulus half-life time (HLT). The asymmetry in terms of N100m magnitude ratio was maximal at modulation HLT of 4 ms and greatly reduced at 0.5 ms and 32 ms which parallels the psychophysical data. fMRI revealed substantial right lateralized activation of Planum temporale in a response to a difference contrast 'ramped-damped' of 4 ms HLT, where we localized N100m sources. Temporally asymmetric sounds were simulated using auditory image model. The extracted carrier salience correlated with both, the N100m magnitude and perceived carrier salience.

auditory processing; temporal asymmetry; magnetoencephalography; functional magnetic resonance imaging

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