In the symptomatic group only, difficulty concentrating and annoyance were also rated higher in the VHFS/US than the reference condition. In both groups, overall discomfort ratings were higher in the VHFS/US condition than the reference condition.
Prior to exposure, participants were assigned either to a symptomatic or an asymptomatic group, based on their prior history of symptoms that they attributed to VHFS/US. The VHFS/US and reference stimuli were presented 4 times, each time for 3 min, during which participants performed a sustained attention task, rated their symptom severity, and had their galvanic skin response (GSR) measured to assess their level of anxiety. To do this, participants were exposed to VHFS/US (at frequencies between 13.5 and 20 kHz and sound pressure levels between 82 and 92 dB) and to a 1 kHz reference stimulus, both at 25 dB above their hearing threshold. This study aimed to establish whether these symptoms are experienced under controlled laboratory conditions and are specific to VHFS/US.
Various adverse symptoms resulting from exposure to very high-frequency sound (VHFS) and ultrasound (US) have previously been reported.
