Feedback control of the auditory periphery: anti-masking effects of middle ear muscles vs. olivocochlear efferents.
Both MEM and MOC systems are sound-evoked reflexes to the auditory periphery which can be elicited by sound in either ear. Both MEM and MOC systems can increase thresholds in the auditory periphery: the MEM system acts by stiffening the ossicular chain, the MOC system by decreasing outer hair cell amplification of sound-induced motion in the inner ear. MEM-induced attenuations are largest for low frequency stimuli, MOC-induced attenuations are largest for mid- to high-frequency sounds. Both MEM and MOC systems can have anti-masking effects. The MEM reflex can decrease the masking of high-frequency signals by low-frequency noise (i.e., the upward spread of masking). The MOC reflex is complementary in that it minimizes masking of high-frequency transient signals by high-frequency continuous noise. MEM anti-masking arises by reducing suppressive masking and can improve masked thresholds at high frequencies. MOC anti-masking arises by counteracting excitatory masking. It does not improve masked thresholds, but can improve the detectability of small suprathreshold intensity increments. Anti-masking effects of both MEM and MOC systems should be reduced in cases of sensorineural hearing loss.
Liberman
M C
MC
Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston, USA. mcl@epl.meei.harvard.edu
Guinan
J J
JJ
D000818:Animals; D002415:Cats; D003051:Cochlea / Q000502:physiology*; D004432:Ear, Middle / Q000502:physiology*; D005246:Feedback; D006801:Humans; D009622:Noise / Q000009:adverse effects; D010470:Perceptual Masking; D012018:Reflex / Q000502:physiology; D013198:Stapedius / Q000502:physiology