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Middle ear transfer function characterisation of chimpanzees (Pan paniscus and Pan troglodytes) and its comparison to the homo sapiens
18 April 2018 (online)
Although human hearing differs from other primates, the functional and morphologic basis of this is unknown. Here we aimed to investigate the middle ear transfer function (METF) of humans' closest living relatives.
Four ears of the chimpanzees pan troglodytes (chimpanzee) and pan paniscus (bonobo) were investigated. Access to the middle ear was achieved over an extended posterior tympanotomy. Sound excitation was achieved in the outer ear canal using laser Doppler vibrometry to measure the footplate vibration and calculate the METF.
The chimpanzee and human METF show general similarities. Characteristic differences are a METF reduction between 4 and 5 kHz with a consecutive increase in the higher frequencies in the chimpanzees. In the lower frequencies the Bonobo's METF is better than the human sound transfer.
The differences in the low frequencies can be explained by the greater tympanic membrane of the chimpanzees. The evolutionary explanation for this difference is most likely the communicational environment of the different species. The differences above 4 kHz seem to be caused in variations of the ossicular chain. However, a definite attribution to specific morphologic differences is not yet possible.