It is widely believed that humans are better than other mammals at
discriminating different frequency sounds. However, mechanisms that could
account for such differences are unknown. Recently the TM has been shown to
support longitudinally propagating waves, and
It is widely believed that humans are better than other mammals at
discriminating different frequency sounds. However, mechanisms that could
account for such differences are unknown. Recently the TM has been shown to
support longitudinally propagating waves, and these waves have been implicated
in tuning properties in a mutant mouse model of hearing. In this study we
investigate the possibility that sharper tuning in humans could result from
differences in human TM waves relative to those of other mammals.
TM wave properties were measured in samples taken from human cadavers,
guinea pigs, and mice. Human TM wave measurements were performed 48 hours
post-mortem. To determine what effect this amount of time could have on TM
properties, we aged mouse cochleae and compared the resulting properties to
those from freshly dissected samples. We found that TM fixed charge density
decreased when samples were aged. We studied the effect of charge on TM waves
using KCl to modulate charge shielding and found that this had little to no
effect on wave properties. We also found that TM wave properties in aged samples
were not significantly different from those in fresh preparations.
These experiments led us to conclude that charge does not play an important
role in TM wave properties. Although surprising, this result is consistent with
the fact that TM waves involve shearing displacements, as opposed to bulk
compression, of the TM.
We performed measure