Analysis of auditory steady-state responses in normal hearing subjects

Abstract

Introduction: Auditory steady-state are electrophysiologic responses elicited by continuous amplitude-modulated tones that can be recorded by surfaces electrodes and allows a more detailed and objective auditory evaluation due to frequency-specific and objective responses analysis. Objective: To evaluate if auditory steady-state responses (recently introduced in Brazil) are really an efficient and trustworthy new technique that might be useful as a routine test in objective audiometry. Material and Method: The present paper has analyzed normal-hearing auditory steady-state responses at frequencies of 500, 1000, 2000 and 4000Hz, recorded from a group of 25 subjects between 21 and 40 years of age. The subjects had hearing thresholds of 0 to 15dB HL, and none of them had any personal history of hearing impairment. Results: Steady-state evoked responses in the frequency-domain were easily detected bilaterally in all of the subjects, using statistical techniques, with intensities varying between 20 and 40dB HL, in at least six of eight studied frequencies, corresponding to 97% of the 200 expected responses. A high concentration of responses (85%) was obtained at intensities below 30dB HL, of which 80% to tones of 500Hz; 84% to tones of 1KHz; 90% to tones of 2KHz, and 86% to tones of 4KHz. Conclusion: Auditory steady-state evoked responses reported here were quite similar to those of other studies conducted in other countries, that is, nearly 15 to 20dB HL from behavioral thresholds. The main advantages over other electrophysiologic auditory evaluation techniques were confirmed as: the recording analysis objectiveness and steady-state frequency-specific responses, so it is believed to be a technique that will soon play an important role in clinical objective audiometry.