Abstract
Several studies showed that the human auditory system is sensitive to infrasound. The present study investigated if non-linear processes within the ear generate distortion products, which may explain the auditory sensitivity to infrasound. Pure-tone infrasound stimuli were presented to the ears of 16 listeners with a low-distortion sound reproduction system via an ear insert. Simultaneously, the sound in the ear canal was recorded with a high-sensitivity probe microphone. In addition, detection thresholds in quiet for these stimuli were determined in all listeners. All of the listeners showed distortion products, which were detected by analyzing the sound recorded in their ear canals during infrasound stimulation, for at least one of the signal frequencies. The sound pressure levels of the distortion products were well below the reference thresholds at the corresponding frequencies. For each signal frequency, the listeners’ detection thresholds in cases with ear-generated distortion products did not differ significantly from those in cases without. Thus, the present data do not support the hypothesis that distortion products play a major role in the auditory perception of infrasound.
Highlights
In the light of a steadily increasing number of reports on infrasound exposure, it is important to understand how humans perceive infrasound, which is defined as sound with frequencies below 20 Hz [1]
They show that an auditory detection threshold can be determined for infrasound stimuli, provided that they have sufficiently high Sound Pressure Levels (SPLs)
Since this study focused on the perception of infrasound by the auditory system, stimuli were delivered exclusively to the ear canal by means of the Low-Distortion Sound Reproduction System (LDREPS) ear insert
Summary
In the light of a steadily increasing number of reports on infrasound exposure, it is important to understand how humans perceive infrasound, which is defined as sound with frequencies below 20 Hz [1]. Several studies indicate that the human auditory system is sensitive to infrasound down to at least 2 Hz (e.g., [2,3,4]; for a review, see [5]). They show that an auditory detection threshold can be determined for infrasound stimuli, provided that they have sufficiently high Sound Pressure Levels (SPLs). Two of them [7, 8] show an activation of the primary auditory cortex This further supports the view that infrasound is processed by the auditory system. The mechanisms underlying this auditory infrasound perception have not yet been fully understood
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