The some vibrations in the inner ear continue even after a sound has ended researchers have found. In the inner ear seems to serve as the mechanical memory of recent sounds. In addition to contributing to sound perception, auditory memory and understanding.
The inner ear contains a structure called the coiled cochlea, fluid filled structure that contains a “basilar” membrane and associated “hair cells” that serves as the organ of hearing.Sound entering the inner ear causes vibrations of the basilar (bottom ) membrane causing the hair cells to bend and vibrate which in turn convey auditory information to the nervous system.
Some hair cells respond to basilar membrane vibrations by producing forces that increase hearing sensitivity and frequency selectivity through mechanisms that are not completely understood.
Dr. Alfred L. Nuttall from the Oregon Hearing Research Centersays his research shows that there is evidence that some tones produce vibrations that continue even after the end of the stimulus.
Using anesthetized guinea pigs, Dr. Nuttall and colleagues recorded basilar membrane motion and hair cell related potentials in response to various sounds. They observed that after-vibrations were dependent on the magnitude and frequency of the sound stimuli and that even minor hearing loss elicited a profound reduction in after-vibrations.
“The after-vibrations ( like an after shock from an earthquake-editor’s note) appear to be driven by sustained force production in the inner ear – a form of short-term memory of past stimulations,” says Dr. Nuttall.
“The ability to detect brief gaps in an ongoing stimulus is critical for speech recognition; gaps need to be longer than a minimal interval to be perceived,” explains Dr. Nutall. “To the extent that after-vibrations excite the auditory nerve fibers, they may explain part of the difficulty in detecting such gaps.” The study is published by Cell Press in Biophysical Journal.
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