High-frequency click-evoked otoacoustic emissions and behavioral thresholds in humans

Relationships between click-evoked otoacoustic emissions (CEOAEs) and behavioral thresholds have not been explored above 5 kHz due to limitations in CEOAE measurement procedures. New techniques were used to measure behavioral thresholds and CEOAEs up to 16 kHz. A long cylindrical tube of 8 mm diameter, serving as a reflectionless termination, was used to calibrate audiometric stimuli and design a wideband CEOAE stimulus. A second click was presented 15 dB above a probe click level that varied over a 44 dB range, and a nonlinear residual procedure extracted a CEOAE from these click responses. In some subjects (age 14-29 years) with normal hearing up to 8 kHz, CEOAE spectral energy and latency were measured up to 16 kHz. Audiometric thresholds were measured using an adaptive yes-no procedure. Comparison of CEOAE and behavioral thresholds suggested a clinical potential of using CEOAEs to screen for high-frequency hearing loss. CEOAE latencies determined from the peak of averaged, filtered temporal envelopes decreased to 1 ms with increasing frequency up to 16 kHz. Individual CEOAE envelopes included both compressively growing longer-delay components consistent with a coherent-reflection source and linearly or expansively growing shorter-delay components consistent with a distortion source. Envelope delays of both components were approximately invariant with level.