Development of high-frequency acoustic source for auditory stimulated magnetoencephalography

Abstract

Hearing can be tested objectively by measuring brain responses due to hearing of certain frequencies. Brain responses can be measured by means of electroencephalography or magnetoencephalography, but non-contact measurements of biomagnetic field allow avoiding difficulties associated with the use of electrodes. Furthermore, magnetoencephalography is sensitive to other brain current configurations than electroencephalography. Acoustic source for auditory evoked magnetoencephalography should deliver the stimulus signal directly to human’s ear and should not interfere with MEG recordings of brain magnetic fields. Cost-efficient setup based on a piezoelectric transducer requires the use of polythene tube for delivering the sound to the subject, which attenuates the tones of frequencies above 9 kHz due to its length. Possible solutions to increase the range of frequencies delivered by auditory source were analyzed. Prototype setup was modified by changing waveguide medium to water and independently by reducing its dimensions, especially the tube length and diameter. Efficiency of acoustic sources was not sufficient and sound pressure level software correction was made. Acoustic properties of developed setups are presented.