Digital Music Exposure Reliably Induces Temporary Threshold Shift in Normal-Hearing Human Subjects

In Brief Objectives: One of the challenges for evaluating new otoprotective agents for potential benefit in human populations is the availability of an established clinical paradigm with real-world relevance. These studies were explicitly designed to develop a real-world digital music exposure that reliably induces temporary threshold shift (TTS) in normal-hearing human subjects. Design: Thirty-three subjects participated in studies that measured effects of digital music player use on hearing. Subjects selected either rock or pop music, which was then presented at 93 to 95 (n = 10), 98 to 100 (n = 11), or 100 to 102 (n = 12) dBA in-ear exposure level for a period of 4 hr. Audiograms and distortion product otoacoustic emissions (DPOAEs) were measured before and after music exposure. Postmusic tests were initiated 15 min, 1 hr 15 min, 2 hr 15 min, and 3 hr 15 min after the exposure ended. Additional tests were conducted the following day and 1 week later. Results: Changes in thresholds after the lowest-level exposure were difficult to distinguish from test–retest variability; however, TTS was reliably detected after higher levels of sound exposure. Changes in audiometric thresholds had a “notch” configuration, with the largest changes observed at 4 kHz (mean = 6.3 ± 3.9 dB; range = 0–14 dB). Recovery was largely complete within the first 4 hr postexposure, and all subjects showed complete recovery of both thresholds and DPOAE measures when tested 1 week postexposure. Conclusions: These data provide insight into the variability of TTS induced by music-player use in a healthy, normal-hearing, young adult population, with music playlist, level, and duration carefully controlled. These data confirm the likelihood of temporary changes in auditory function after digital music-player use. Such data are essential for the development of a human clinical trial protocol that provides a highly powered design for evaluating novel therapeutics in human clinical trials. Care must be taken to fully inform potential subjects in future TTS studies, including protective agent evaluations, that some noise exposures have resulted in neural degeneration in animal models, even when both audiometric thresholds and DPOAE levels returned to pre-exposure values. The authors describe real-world digital music exposures that reliably induce small temporary threshold shift in normal hearing human subjects. Effects of digital audio player use on hearing sensitivity were measured in 33 subjects that listened to rock or pop music playlists for four hours at ~94 (n=10), ~99 (n=11), or ~100 (n=12) dB-A in-ear level. Temporary threshold shift was greatest at 4 kHz. The authors describe variability of temporary threshold shift induced by music player use in this healthy, normal-hearing, young adult population, and demonstrate complete recovery. The authors propose the protocol as appropriate for evaluation of interventions of otoprotection potential, with the requirement that subjects be fully informed of potential risks.