Hearing examinationsThe standard pure-tone air conduction audiometry (PTA) and extended high-frequency audiometry (EHFA) were performed in all participants of the study. The auditory rest before the audiological evaluations was 14 h.Hearing threshold levels (HTLs) for each ear were determined for both standard frequencies from 0.25 to 8 kHz (0.250, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, and 8 kHz) as well as extended frequencies from 8 to 18 kHz (8, 9, 10, 11.2, 12.5, 14, 16, and 18 kHz) with 5 dB steps. The bracketing method according to ISO 8253-1:2010[14] has been used in case of standard pure-tone audiometry. The similar methodology has been applied for EHFA. But in the latter case, the initial familiarization was performed using a tone of 11.2 kHz. The order of tones was from 11.2 upward to 18 kHz, followed by the lower frequency range, in the descending order (i.e., from 11.2 to 8 kHz). However, HTLs at 18 kHz was not included into analysis due to many missing data.The PTA was always performed first, followed by the EHFA. In both cases, the right ear was tested first. The hearing examinations were conducted with the VIDEOMED Smart Solution (Poland) clinical audiometer, model AUDIO 4002 with the Holmberg GMBH & CO. KG Electroacoustik (Germany) headphones type HOLMCO P-81 for the PTA, and the Sennheiser Electronic GmbH & Co. KG (Germany) headphones type HDA 200 for EHFA. Prior to the audiological evaluations, otoscopy was performed.Hearing tests were conducted in a quiet room located in the call center where the A-weighted equivalent-continuous SPL of background noise did not exceed 35 dBA.