INTERACTION EFFECTS IN AUDITORY STEADY STATE RESPONSES (ASSR)

Papakonstantinou A, Riedel H, Kollmeier B.

Carl von Ossietzky University of Oldenburg, Germany.

Background: Auditory steady-state responses (ASSR) are evoked responses generated by stimuli with periodic envelope fluctuations. Multiple ASSRs (MASSR) have been suggested as an audiological technique to record thresholds for different frequencies and ears simultaneously reducing measurement time. However, at least at high stimulation levels, strong interaction reduce the response amplitudes.

Aim: The present study investigates ASSR interaction at a moderate stimulus level of 60 dB SPL.

Methods: A stimulus with two carriers (fc1 = 1 kHz, fc2 = 2 kHz) and modulation rates near 40 Hz (fm1 = 38 Hz, fm2 = 42 Hz) was used. ASSRs were measured for 20 normal-hearing subjects and characterized by the averaged amplitude and SNR of the Fourier components at the two modulation frequencies.

Results: ASSR amplitudes were generally larger for fc1 compared to fc2. Unmodulated interferers had no influence on ASSR amplitudes. Modulated interferers, presented ipsi- or contralaterally to the probe ear, both significantly reduced the ASSR amplitude at the probe-frequency, on average by 8.7%. The ASSR at the beating frequency (fm2 – fm1= 4 Hz) was significant in the grand average amplitude spectrum for ipsi- and contralateral interferers.

Conclusions: Since ASSR amplitude reduction is similar for ipsi- and contralateral interferers, modulation interaction appears to be dominated by central rather than peripheral processes. Spectral energy at the beating frequency indicate a central nonlinearity. A level of 60 dB SPL can easily be reached during an ASSR hearing screening of an adult with mild sensorineural hearing-impairment. Therefore, interactions should be taken into account when estimating thresholds from MASSR.

E-mail: alexandra.papakonstantinou@uni-oldenburg.de