Comparison of earphone radiation recorded from hearing impaired subjects and a resistor network simulator

Electromagnetic radiation emitted by earphones is a potential source of contamination of auditory evoked potentials, particularly when long-duration stimuli are used to evoke the response. One practical solution to this problem would be to estimate the magnitude and characteristics of this earphone radiation so that an appropriate choice of earphone is made. With this aim, earphone radiation measures obtained from a resistor network simulator laid out over the dimensions of an average head were compared with those obtained from three hearing impaired subjects to determine the efficacy of the simulator in estimating the magnitude of this radiation. Results indicated a close agreement between these measures suggesting that the simulator measures are realistic. It was shown that the earphone radiation (i) increases linearly with stimulus intensity; (ii) varies systematically as a function of recording configuration; and (iii) recorded in the simulator can be used to subtract out earphone radiation contaminating evoked responses recorded from subjects using unshielded earphones. Based on these results it was concluded that the simulator provides a practical means to simulate real recordings, at least for the purposes of estimating stimulus artifact that may contaminate auditory evoked potentials to sustained stimuli.