Our hearing is remarkable for its physical capabilities. We can discern sounds at frequencies up to 20 kHz, a bandwidth one thousandfold that of our vision. At the auditory threshold, our ears detect vibrations of only ±0.3 nm, an atomic dimension.

Finally, our hearing responds over twelve order of magnitude in intensity, a range unmatched by other sensory systems or indeed by manmade detectors. Uniquely among vertebrate sensory receptors, the ear's mechanoreceptive hair cells amplify their inputs by means of an active process that increases responsiveness to sound, sharpens frequency selectivity, and compresses the dynamic range of hearing.

An overly exuberant active process can even cause the spontaneous emission of sound from an ear! Each hair cell uses its hair bundle, an elaborate array of tiny biological strain gauges, both to transduce mechanical stimuli and to implement the active process. Mechanical amplification is accomplished through the interaction of negative hair-bundle stiffness with the activity of the motor protein myosin-1c.

The operation of the active process near a dynamical instability, the Hopf bifurcation, explains many of the characteristics of our hearing.

About Dr. Hudspeth:

Served on the faculties of the California Institute of Technology, the University of California, San Francisco, and the University of Texas Southwestern Medical Center.
Honors include the Spencer Award from Columbia University, the Lamport Award from the New York Academy of Sciences, the Cole Award from the Biophysical Society, the Dana Award from the Charles A. Dana Foundation, among others.
Serves as member of the National Academy of Sciences and the American Academy of Arts and Sciences.

The NIH Director's Wednesday Afternoon Lecture Series includes weekly scientific talks by some of the top researchers in the biomedical sciences worldwide.