Low-frequency exposure temporarily activates new otoacoustic emissions that were previously absent in most ears.

Evidence

The effect of the 80 dBA LF exposure on quadratic (QDP) and cubic (CDP) OAEs is shown in Fig. 1a and b , respectively. In 14 out of 20 tested subjects, the LF exposure induced a subsequent increase of the QDP level lasting for about 60 to 90 s (see Fig. 1a ). QDP levels increased with a median of 3.4 dB. In most cases, this QDP increase was followed by a similar QDP decrease (median: ‑2.4 dB), at about 120–150 s post-exposure. This decrease slowly recovered to pre-exposure QDP levels. The median duration of the overall oscillatory change of the QDP level was 214 s. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3703

Both ears of 45 young, normal-hearing subjects were screened for SOAEs. 33 subjects showed at least one SOAE in one ear. Overall we could record in the open meatus about 52 % of those SOAEs detectable in a sound-attenuated room and a closed-ear recording technique. The remaining 48 % were not significantly above the much higher noise floor of the free-field, open-meatus measurement. Exemplary measurements of both permanent and transient SOAEs are shown in Fig. 3c and d in the same format as Fig. 2 . Indeed many of those 48 % SOAEs that had been initially identified in the closed-meatus measurements, but could no longer be detected in the open meatus, appeared directly after the LF exposure for a short time period, before falling again below the noise floor (Fig. 3d ). These data clearly show that Bouncing of SOAEs can indeed be elicited by free-field exposure to LF sound sources of natural or anthropogenic origin. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3728

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. The duration of the level and frequency changes was 67.5 s (47.5 s, 90 s). New SOAEs started to arise within 12.5 s (5 s, 25 s) after LF sound offset and reached a level maximum at 50 s (35 s, 62.5 s) after LF offset. The maximum SOAE level was ‑0.3 dB SPL (‑4.1 dB SPL, 4.9 dB SPL) with a signal to noise ratio of 13.8 dB (11.9 dB, 17.6 dB). The difference between the new SOAE frequency maximum and minimum was 4 Cent (1 Cent, 6 Cent). The time course of level and frequency changes was almost identical and maximum level and frequency changes coincided. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3727

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…, 3721

Categorization

• QUESTION: What mechanism explains the oscillatory increase-then-decrease of quadratic distortion products after low-frequency offset? Is it a slow outer hair cell state change?
• SEED: The discovery that low-frequency sound can ‘switch on’ previously silent cochlear emission sites is a strong hook for a pop-science article about the inner ear being more labile than textbook models suggest.
• corroborated: 4 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 3703; Dijk, Pim van, Physiology, Psychoacoustics and…, 3728; Dijk, Pim van, Physiology, Psychoacoustics and…, 3727 (+1 more)