Confirmation of previous results of the occlusion effect through auditory steady-state responses in normal-hearing adults

Context: The occlusion effect (OE) is a well-known phenomenon in audiology clinical practice. Hence, some authors recommend the application of a correction factor to compensate for the OE. However, only two studies have assessed the OE using auditory steady-state responses (ASSRs). Aims: The aim of this study is to confirm the findings from previous ASSRs studies of the OE for a larger sample of normal-hearing adults. Settings and Design: Thirty-two normal-hearing adults (32 ears) with a mean age of 21 2 years participated in this study. For each participant, one ear was selected at random, and the first measures to be obtained (occluded or unoccluded) were randomly determined. Subjects and Methods: The stimulus comprised a combination of four sinusoidal carrier tones, 500, 1000, 2000, and 4000 Hz, modulated in amplitude (95% depth) at the following rates: 104.2, 107.8, 111.4, and 115 Hz, respectively. It was presented through bone conduction for each participant under two different conditions (occluded and unoccluded ear). The overall ambient noise was 52 dB sound pressure level. Statistical Analysis Used: Repeated-measures analysis of variances was performed to compare occluded and unoccluded ASSR thresholds and amplitudes at 30 dB hearing level for 500, 1000, 2000, and 4000 Hz. Results: Occlusion caused a significant decrease of bone-conducted ASSR thresholds at low frequencies and a significant increase at 4000 Hz. Mean ASSR amplitudes were significantly higher after occlusion at low frequencies. However, some participants showed no OE at frequencies at which it is expected to be present. Conclusions: Despite the high ambient noise issue, results of previous studies are confirmed here in a larger sample of cases.