PHYSICAL MATHEMATICS SEMINAR


TOPIC:		ADDING A DIMENSION TO COCHLEAR MECHANICS

SPEAKER:	ELIZABETH S. OLSON
		Department of Physics
		Princeton University


ABSTRACT:

The auditory inner ear, the cochlea, is a spiral of fluid and sensory
tissue encased in bone.  Sound energy from the environment enters the
cochlea by the plunging action of the third middle ear bone, the stapes.  
In the cochlea, the sound stimulus is translated into a neural signal via
specialized transducer "hair cells" within the sensory tissue.  The fluid
dynamics of the cochlea shapes the stimulus that is delivered to the hair
cells.  Incoming sound is sorted by frequency so that high frequencies
cause the sensory tissue to move maximally at locations close to the
stapes, and low frequency sound causes maximal motion far down the spiral.  
Beyond frequency sorting, the cochlea amplifies small signals, effectively
compressing a large range of input sound pressure into a much smaller
range of output hair cell voltage.  This amplification involves mechanical
action by a second set of hair cells.  The basis for frequency separation
and small signal amplification in the cochlea is not clear, even at the
most fundamental levels.  In the work described here, measurements of
intracochlear pressure close to the sensory tissue were made.  Pressure
measurements complement measurements of sensory tissue motion.  The goal
was to use simultaneous measures of these complementary quantities to
examine the mechanical properties of the sensory tissue, looking in
particular for resonance and amplification.  The measurements also probed
the fluid component of cochlear mechanics, and suggested that this
component's role in frequency tuning merits further investigation.

DATE:		TUESDAY, APRIL 11, 2000

TIME:		2:30 PM

LOCATION:	Room 2-338

Refreshments will be served at 3:30 PM in Room 2-349.

					Massachusetts Institute of Technology
					Department of Mathematics
					Cambridge, MA  02139