Evoked acoustic emissions from within normal and abnormal human ears: comparison with audiometric and electrocochleographic findings.

Input--output amplitude behaviour of evoked acoustic emissions ('echoes') to click- and toneburst stimuli can be approximated by R(tau) alpha SPT(tau) where R is response amplitude, S stimulus amplitude and p(tau) is an exponent dependent on latency tau. p(tau) varies linearly from one to zero for post stimulus times (PST) between 5 and about 25 ms, thus indicating increasing nonlinearity with increasing latency. Latencies of echoes after toneburst stimulation decrease with increasing frequency. The latencies seem to be built up from twice the traveling wave time (from the acoustic source to the cochlear partition site of reception) plus twice the transduction filter response times. Adaptative behaviour of the echo-response on varying interstimulus interval (ISI) is not observed. If echoes are present, with frequency fECHO, audiogram losses at fECHO do not exceed 15 dB. Compound action potential (AP) thresholds, obained by electrocohleography (ECoG) confirm this 15 dB criterion and indicate that the 15 dB loss should be of cochlear origin.