Abstract
This magnetoencephalography (MEG) study investigated evoked ON and OFF responses to ramped and damped sounds in normal-hearing human adults. Two pairs of stimuli that differed in spectral complexity were used in a passive listening task; each pair contained identical acoustical properties except for the intensity envelope. Behavioral duration judgment was conducted in separate sessions, which replicated the perceptual bias in favour of the ramped sounds and the effect of spectral complexity on perceived duration asymmetry. MEG results showed similar cortical sites for the ON and OFF responses. There was a dominant ON response with stronger phase-locking factor (PLF) in the alpha (8–14 Hz) and theta (4–8 Hz) bands for the damped sounds. In contrast, the OFF response for sounds with rising intensity was associated with stronger PLF in the gamma band (30–70 Hz). Exploratory correlation analysis showed that the OFF response in the left auditory cortex was a good predictor of the perceived temporal asymmetry for the spectrally simpler pair. The results indicate distinct asymmetry in ON and OFF responses and neural oscillation patterns associated with the dynamic intensity changes, which provides important preliminary data for future studies to examine how the auditory system develops such an asymmetry as a function of age and learning experience and whether the absence of asymmetry or abnormal ON and OFF responses can be taken as a biomarker for certain neurological conditions associated with auditory processing deficits.
Highlights
One fundamental property of the human auditory system is to automatically detect and respond to sound sources and changes
temporal asymmetry index (TAI) measures, we looked at the ON and OFF responses in the left and right hemispheres separately in terms of equivalent current dipole (ECD) amplitude and latency data
The behavioral results replicated previous studies that ramped sounds were perceived to be longer in subjective duration compared to damped sounds
Summary
One fundamental property of the human auditory system is to automatically detect and respond to sound sources and changes. Schlauch et al (2001) found that ramped sounds ranging from 10 to 200 ms were perceived to be longer than the time-reversed damped sounds, which had identical physical duration as well as long-term spectral power and envelope spectra. This overestimation was found for sounds longer than 200 ms [6]. When the carrier is spectrally more complex than a sinusoidal tone, the asymmetry decreases or may even disappear [1,3,10,13,14]
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