Activation in human auditory cortex in relation to the loudness and unpleasantness of low-frequency and infrasound stimuli

Abstract

Low frequency noise (LFS) and infrasound (IS) are controversially discussed as potential causes of annoyance and distress experienced by many people. However, the perception mechanisms for IS in the human auditory system are not completely understood yet. In the present study, sinusoids at 32 Hz (at the lower limit of melodic pitch for tonal stimulation), as well as 8 Hz (IS range) were presented to a group of 20 normal hearing subjects, using monaural stimulation via a loudspeaker sound source coupled to the ear canal by a long silicone rubber tube. Each participant attended two experimental sessions. In the first session, participants performed a categorical loudness scaling procedure as well as an unpleasantness rating task in a sound booth. In the second session, the loudness scaling procedure was repeated while brain activation was measured using functional magnetic resonance imaging (fMRI). Subsequently, activation data were collected for the respective stimuli presented at fixed levels adjusted to the individual loudness judgments. Silent trials were included as a baseline condition. Our results indicate that the brain regions involved in processing LFS and IS are similar to those for sounds in the typical audio frequency range, i.e., mainly primary and secondary auditory cortex (AC). In spite of large variation across listeners with respect to judgments of loudness and unpleasantness, neural correlates of these interindividual differences could not yet be identified. Still, for individual listeners, fMRI activation in the AC was more closely related to individual perception than to the physical stimulus level.

A psychoacoustical study to investigate the perceived unpleasantness of infrasound combined with audio-frequency sound

“…Particularly high inter-individual differences were found for psychoacoustic variables including infrasound as in other studies (e.g. [4,5,31]). The unpleasantness ratings using the numerical scale can only in part be related to the individual detection threshold for infrasound.…”

“…Moreover, this infrasound stimulus is more unpleasant than the broadband stimulus at 70 phon and it has about the same unpleasantness as the 1000 Hz stimulus at 70 phon. This indicates that the unpleasantness cannot be derived directly from the perceived loudness which is in line with the results of Behler and Uppenkamp [31]. In addition, it is important to keep in mind that ratings of the unpleasantness of infrasound as a function of the perceived loudness can vary considerably across individuals [31].…”

Is infrasound perceived by the auditory system through distortions?

“…They show that an auditory detection threshold can be determined also for infrasound stimuli, provided that they have sufficiently high Sound Pressure Levels (SPLs). Recent studies on human brain activation [6][7][8] show that the brain responds to infrasound that is being presented to the ear, at threshold and at higher loudness levels. Two of them [7,8] show an activation of the primary auditory cortex.…”

Health Effects Related to Wind Turbine Sound: An Update

“…Behler and Uppenkamp [84] investigated the loudness and unpleasantness of either 8 Hz or 32 Hz sound presented to 19 young, normal hearing persons. The maximum sound level was 140 dB.…”