Ipsilateral and contralateral recordings of the 40-Hz auditory steady state response (ASSR): Which one is better?

Objective: Few studies have investigated the auditory steady state response (ASSR) thresholds evoked by ipsilateral and contralateral stimulation. The present study was conducted to compare 40-Hz ASSR thresholds between ipsilateral and contralateral recordings at specific test frequencies. Methods: Twenty young female subjects with normal hearing bilaterally (hearing level <= 20 dB HL across speech frequencies) were included in the study. One-octave-wide narrow band CE-chirp (R) stimuli centred at 500, 1000, 2000 and 4000 Hz with 40 Hz modulation frequency (MF) were presented ipsilaterally and contralaterally to each subject through insert earphones. The ASSR thresholds were obtained for each recording condition. Results: The mean ASSR thresholds were higher for contralateral recording than for ipsilateral recording at all test frequencies, but analysis using the paired t-test revealed that the differences were not significant at any of the test frequencies (p > 0.05). Comparing the ASSR thresholds among the test frequencies for the two recording conditions, there were no significant differences as determined using one-way ANOVA (p > 0.05). Conclusion: The 40-Hz ASSR thresholds can be reliably recorded with ipsilateral and contralateral stimulation. For objective determination of hearing thresholds in young women, either ipsilateral or contralateral ASSR recording is appropriate. Nevertheless, the combination of both recordings might increase the diagnostic value of 40-Hz ASSR in estimating behavioural hearing thresholds.