The Journal of Neuroscience, October 1, 1999, 19(19):8704-8711
Conductive Hearing Loss Produces a Reversible Binaural
Hearing Impairment
David R.
Moore,
Jemma E.
Hine,
Ze Dong
Jiang,
Hiroaki
Matsuda,
Carl H.
Parsons, and
Andrew J.
King
University Laboratory of Physiology, Oxford OX1 3PT, United Kingdom
Conductive hearing loss, produced by otitis media with effusion, is
widespread in young children. However, little is known about its short-
or long-term effects on hearing or the brain. To study the consequences
of a conductive loss for the perception and processing of sounds, we
plugged the left ear canal of ferrets for 7-15 months during either
infancy or adulthood. Before or during plugging, the ferrets were
trained to perform a binaural task requiring the detection of a 500 Hz
tone, positioned 90° to the right, that was masked by two sources of
broad-band noise. In one condition ("control"), both noise sources
were 90° right and, in the second condition ("bilateral"), one
noise source was moved to 90° left. Normal ferrets showed binaural
unmasking: tone detection thresholds were lower (mean 10.1 dB) for the
bilateral condition than for the control condition. Both groups of
ear-plugged ferrets had reduced unmasking; the mean residual unmasking
was 2.3 dB for the infant and 0.7 dB for the adult ear-plugged animals. After unplugging, unmasking increased in both groups (infant, 7.1 dB;
adult, 6.9 dB) but not to normal levels. Repeated testing during the 22 months after unplugging revealed a gradual return to normal levels of
unmasking. These results show that a unilateral conductive hearing
loss, in either infancy or adulthood, impairs binaural hearing both
during and after the hearing loss. They show scant evidence for
adaptation to the plug and demonstrate a recovery from the impairment
that occurs over a period of several months after restoration of normal
peripheral function.
Key words:
deafness; auditory plasticity; otitis media; binaural
unmasking; ferret; ear plug
Copyright © 1999 Society for Neuroscience 0270-6474/99/19198704-08$05.00/0
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