Time course of suppression of spontaneous otoacoustic emissions

Abstract

Few data are available on the time course of suppression, by externally introduced sounds, of spontaneous otoacoustic emissions (SOAEs), and none have been presented for humans. By means of extensive averaging in the time domain and digital filtering, we have obtained such data for the (synchronized) SOAE produced by the first author's right ear (7529 Hz, 10–16 dB SPL). Upon presentation of a tone pip, there is a latency (1.2 ms at high suppressor levels, longer at lower levels) before any change can be detected in SOAE level. Most of the suppression then develops over an interval lasting 1.5–2.0 ms, but this relatively fast onset is followed by a roughly exponential slope with a time constant longer than 4 ms. At low suppressor levels, the latency to the beginning of recovery from suppression may be similar to the latency to suppression onset; for higher suppressor levels, the latency may be several tens of ms and recovery may not be complete before 100 ms. Given the uncertainty that still exists on travel times in the human basilar membrane, our data cannot rule out the possibility that the latency to onset of suppression matches the travel time in the cochlea to and from the site of origin of the SOAE. [Work supported by NIH Grant NS-12125.]