I have a background in psychology, audiology and neuroscience. In my research I have people listen to carefully designed tones and noises, and from their responses I come up with theories about how the auditory system works. I use stimuli that are very precisely controlled in time and in frequency, such as tones and noises, because the auditory system is so complex that it is only by using very controlled stimuli that we can get a clear picture of what is happening. Over the past few years I have been working on a very exciting line of research examining how the auditory system changes as it is stimulated by sound. One example of this sort of change is the fact that a brief tone that occurs at the onset of a longer duration noise is harder to hear than one that is delayed from the onset of the noise. This effect, often called overshoot, has been attributed to effects as peripheral as adaptation in the VIIIth nerve, and as central as attention. In my research, I have found strong evidence that overshoot actually results from the auditory system turning down amplification in the cochlea as it is stimulated by sound. This is a critically important finding, because it explains a wealth of other very basic psychophysical data in addition to the overshoot effect. Also, it has been known for some time that there is efferent feedback to the cochlea, which has been shown to turn down cochlear amplification in anesthetized animals, but it has been difficult to demonstrate its effects behaviorally. The results of my research in awake, behaving humans suggest that the efferent system plays a key role in auditory perception. This also has important clinical applications. In the past, we have tended to compare normal and impaired hearing as if the auditory system were static. My research suggests that the normal auditory system is changing in a dynamic manner in response to sound, while the impaired system does not, and this could explain why hearing impairment causes more difficulty than might be expected from a simple elevation in hearing threshold.