Effect of head-movment on sound-field auditory steady state response meansurement

Sound-field auditory steady-state response (ASSR) is an objective alternative for hearing aid fitting validation in infants. For including the hearing aid in the signal path, the stimulus is presented via a loudspeaker. In this way, ASSR is affected by the head orientation of the test subject and the room acoustics. Eleven normal hearing participants were tested for three static head-orientations, defined according to the position of the stimulated ear relative to the loudspeaker in two different rooms. A speech modified NB CE-Chirps stimulus was used in order to eventually force the hearing aid under test to provide the correct gain. The rooms chosen for measurement were an IEC listening room (T30∼ 0.5 s) and an anechoic chamber (reference condition). A dynamic head-orientation condition comparable to a real head-movement was simulated by randomly combining the responses from the three static head-orientation measurements. The results show a limited influence of head movement on ASSR level. However, in the 4000 Hz band, a significant reduction in ASSR level was observed when the test ear turned away from the loudspeaker. The overall mean ASSR level in the IEC room was reduced by 2.5 dB with reference to the anechoic condition.