청성지속반응(auditory steady-state response, ASSR)은 연속적인 음 자극(continuous acoustic stimuli)에 대한 청각전도로의 반응으로 특히 고심도 난청의 청력을 추정할 수 있는 대표적인 객관적 검사로 알려져 있다.12) 이러한 ASSR은 변조된 순음(pure tone)에 의해서 유발되기 때문에 청성뇌간반응(auditory brainstem response, ABR) 측정 시 주로 사용하는 클릭음(click)보다 와우의 좁은 부위를 자극하게 되어 주파수 특이성이 더 높고,9) 자동반응탐지 알고리즘(automatic response detection algorithm)을 사용하기 때문에 결과 판정에 있어서 검사자의 경험이나 주관적 판단에 근거하여 반응의 유무를 판단하는 ABR의 단점을 보완할 수 있어서 좀 더 객관적이고, 신뢰도 있는 검 사가 가능해졌다.3) 또한 클릭음이나 tone burst 자극 시 발생하는 자극음의 왜곡현상이 적게 발생하고, 높은 진폭의 자극음으로 측정할 수 있기 때문에 고심도 난청자, 인공와우 이식대상자 및 주관적인 검사가 어려운 사람들의 청력평가에 유용하게 사용될 수 있다.
The purpose of this study was to find out effects of factors related with stimuli on ASSR in normal hearing and sensory-neural hearing loss (SNHL). We compared the ASSR amplitudes, the time required to detect significant responses, ASSR thresholds and differences between ASSR and pure tone thresholds for each exponent of modulation and stimulus level. Subjects included 35 persons (68 ears) with normal hearing and 24 persons (44 ears) with SNHL. A clinical AC 33 audiometer (Interacoustics) was used to evaluate pure tone thresholds. ASSR was obtained using MASTER system (version, 2.01) at carrier frequencies of 500, 1,000, 2,000, 4,000 Hz with modulation frequencies of 82-99 Hz and the exponent of modulation (N) 1 or 2 (100% AM/20% FM vs 100% AM2/20% FM). Results were as follows. Firstly, ASSR amplitudes with AM2/FM was significantly larger than those with AM/FM by 9.66 % and 3.32 % at each stimulus level (50 dBHL vs 30 dBHL) in normal hearing and by 12.54 % at 10SL in SNHL. Secondly, the time required to detect significant responses was not significantly different for each exponent of modulation and stimulus level in both normal hearing and SNHL. Thirdly, ASSR thresholds and differences between ASSR and pure tone thresholds with AM2/FM is significantly lower and smaller than those with AM/FM in both normal hearing and SNHL. The results indicate that ASSR with the exponent of modulation from 1 to 2 may produce larger amplitudes and take the short time to obtain significant responses and may produce lower thresholds andsmallerdifferences between ASSR and pure tone thresholds. Therefore the exponent of 2 for amplitude modulation of mixed modulation can be used for estimating hearing level in both normal hearing and SNHL. KEY WORDS：Auditory steady-state response (ASSR)·The exponent of modulation.
INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES
