The influence of carotid arterial sounds on hearing sensitivity in mammals

Abstract

Pulsations of the internal carotid and stapedial arteries produce unwanted sounds (noise) in the middle ear cavity which influence hearing in some mammals. ‘Noise’ pressure levels calculated from pulse rates, volume pulsations of the arteries, and Fourier analysis of arterial waveforms, correlate well with low frequency thresholds of hearing in the Long‐eared hedgehog, Tree shrew and Kangaroo rat. In mammals adapted to hear low frequency sounds, such as the Kangaroo rat and fossorial insectivores, the arteries are enclosed in noise attenuating bony tubes. However, most small mammals possess extended high frequency hearing with little sensitivity at the low frequencies of the arterial sounds. In lower tetrapods such as anurans and most lizards, the broad connection between the middle ear cavity and the pharynx creates a leakage pathway which greatly reduces the noise from the stapedial artery. It is probably for these reasons that the large intratympanic arteries did not disturb hearing in early mammals or submammalian forms.