Detection Thresholds for Combined Infrasound and Audio-Frequency Stimuli

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.