Speaker
Description
Most studies of hearing are based on Europeans or Asians or their descendants, in, e.g., N. America. There is little data on other human populations. The San people of southern Africa represent one of the oldest distinct human populations, being almost completely separate from all other groups for > 100k years. We report a study in young adults belonging to the Ju/’huansi of the Nyae Nyae San community in Namibia compared to West European students in Groningen. The studies were approved by relevant review boards, the local San community and the Namibian government. A closed insert microphone system (Etymotic ER10B) was used for measuring audiograms, spontaneous otoacoustic emissions (SOAE), suppression tuning of SOAE, and stimulus frequency emissions (SFOAE). Audiograms were indistinguishable in the Namibian and European groups. SOAE peak values were higher in Namibian subjects, both in the highest peak frequencies (13.7 kHz in in Namibians vs. 9.6 kHz in Europeans) and highest levels (19.0 vs. 16.4 dB SPL, respectively). Suppression tuning curves had a V- shape with additional side-lobes on the high-frequency slope. While the main V-shape was similar in both groups, sidelobes were more numerous and deeper in Namibians. SFOAE amplitudes and phase delays were similar between the groups. However, SFOAE amplitudes were usually lower in the Europeans at higher frequencies.In the absence of differences in the audiogram, the reduced number SOAE and lower amplitudes of SFOAE at higher frequencies, suggest a previously unknown form of hidden hearing loss in the Europeans. The pronounced sidelobes in the suppression tuning curves of Namibians suggest enhanced coupling along the cochlear partition.