Low-frequency sound exposure triggers long-lasting damped oscillations in spontaneous otoacoustic emissions.

Evidence

After LF sound stimulation, 56 of these 80 SOAEs increased in both sound level and frequency. This increase was followed by a decrease of both level and frequency relative to pre-exposure (see Fig. 2a ). — Dijk, Pim van, Physiology, Psychoacoustics and…, 3703

17 of 21 tested subjects revealed an overall of 56 new SOAEs, which had not been measurable before LF stimulation (see Fig. 2b ). These new SOAEs were characterized by an initial level and frequency increase, qualitatively similar to the pre-existing SOAEs. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3703

17 of 21 tested subjects revealed an overall of 56 new SOAEs, which had not been measurable before LF stimulation (see Fig. 2b ). These new SOAEs were characterized by an initial level and frequency increase, qualitatively similar to the pre-existing SOAEs. Comparable to the enhancing half cycle of Bouncing SOAEs, their level and frequency oscillated before they disappeared into the noise floor. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3711

We recorded 80 SOAEs from 27 ears of 16 young, normal-hearing subjects. The median SOAE sound levels were 0.6 dB SPL (first and third quartiles, ‑4.5 dB SPL; 4.0 dB SPL) with a signal-to-noise ratio of 16.6 dB (11.6 dB, 23.5 dB). After LF sound stimulation, 56 of these 80 SOAEs increased in both sound level and frequency. This increase was followed by a decrease of both level and frequency relative to pre-exposure (see Fig. 2a ). In 10 of the 80 pre-exposure SOAEs, we observed an inverted pattern with an initial level and frequency decrease, followed by a level and frequency increase. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3719

SOAE leveland frequency oscillations were fitted with an (inverted-phase) underdamped sinusoidal oscillation. The period of the fitted sinusoid was 257 s (202 s, 294 s) for the level time course and 252 s (215 s, 367 s) for the frequency time course. The time constant of the damped sinusoid for level changes was 120 s (76 s, 157 s) and for frequency changes 94 s (58 s, 141 s). SOAE frequency changes amounted to 5 Cent (4 Cent, 9 Cent) with peak values of 25 Cent. Relative to the SOAE frequency in the control condition, the frequency showed initial maximum increases of 4 Cent (3 Cent, 7 Cent), followed by maximum decreases of 1 Cent (0 Cent, 2 Cent). — Dijk, Pim van, Physiology, Psychoacoustics and…, 3703

Categorization

• QUESTION: What mechanism explains de novo SOAE generation in ~71% of subjects? Is it a change in the cochlear amplifier’s operating point, or a transient gain shift at specific cochlear sites?
• XREF: Connects to the reader’s wider knowledge of otoacoustic emissions and cochlear mechanics; the two-thirds-majority / one-eighth-inverted asymmetry is a striking empirical regularity worth cross-checking against cochlear model literature. — connects to: Spontaneous emissions respond to suppressors with a time constant near 15 ms; Delayed otoacoustic emissions obey linear superposition at low amplitudes — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 296; Otoacoustic emission delay times shrink from 20 ms to 4 ms as frequency rises (+6 more)
• corroborated: 10 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 3703; Dijk, Pim van, Physiology, Psychoacoustics and…, 3711; Dijk, Pim van, Physiology, Psychoacoustics and…, 3719

Broader Connections

• Low-frequency sound’s after-effects arise from calcium homeostasis in outer hair cells #expands (0.72) — Dijk, Pim van, Physiology, Psychoacoustics and…, 3701