Abstract
This study investigated whether the presence of audio sound (20 Hz < frequency f < 20 kHz) influences the detection threshold for infrasound (f < 20 Hz), and, vice versa, whether the presence of infrasound influences the detection threshold for audio sound. Monaural detection thresholds of thirteen otologically normal listeners were repeatedly determined for infrasound stimuli (sinusoids at 5 Hz and at 12 Hz) and for audio sound stimuli (sinusoids and bandlimited pink noise), separately and in presence of the respective other sound type. The measurements were performed with an adaptive 1-up-2-down 3-alternative forced-choice (3-AFC) procedure. Threshold levels for infrasound stimuli were not affected by audio sound at +5 dB sensation level (SL), but they were significantly increased by the presence of some of the audio sound stimuli presented at +50 dB SL. For example, thresholds for the detection of infrasound increased on average by around 5 dB when simultaneously presented with a pink-noise stimulus (frequency range: 250 Hz– 4000 Hz). On the other hand, the presence of infrasound with levels up to +10 dB SL did not cause any significant change in the detection thresholds for audio sound. This could be an indication that infrasound might even be more annoying in a quiet environment.
Highlights
It is well established that humans are able to perceive infrasound
A pilot study conducted prior to the actual study presented in this paper indicated small or no effects of IS presented up to +10 dB sensation level (SL) on the threshold levels for AS stimuli, but a considerable increase of the individual threshold level for the IS stimuli caused by the presence of AS background stimuli [18]
The ANOVA for AS threshold levels revealed a significant effect of target stimulus (p < 0.001), background stimulus (p < 0.001) and session (p = 0.034), but no significant interaction between factors
Summary
It is well established that humans are able to perceive infrasound (abbr. IS, frequency f < 20 Hz) at least down to 2 Hz (see, e.g. the review paper by Møller and Pedersen [1]). IS stimuli were sinusoids at 5 Hz and at 12 Hz. The aim was to investigate whether the effects on the detection threshold measurements are similar for IS stimuli at different frequencies, which are well below the lower frequency limit for AS (between 16 Hz and 20 Hz), and which have a distance of more than one octave to each other, taking into account that the sound source system is applicable for stimulation with IS down to 4 Hz [19]. The study by Salt et al [14] showed that infrasonic responses from guinea pigs recorded as endolymphatic potentials were suppressed by AS with increasing sound pressure level of AS. This indicates that there might be other physiological effects causing the threshold increase for IS
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