Determining the Upper Limits of Stimulation for Auditory Steady-State Response Measurements

Abstract

Objective: 

To determine the maximum stimulus levels at which a measured auditory steady-state response (ASSR) can be assumed to be a reliable measure of auditory thresholds.

Design: 

ASSR thresholds were measured at octave frequencies from 500 to 4000 Hz in 10 subjects with profound hearing loss. These subjects provided no behavioral responses to sound at the limits of pure-tone audiometers and at the limits of the stimulus levels produced by the ASSR device. Subjects were divided into two groups of five, with repeated measures obtained within the same session in one group and repeated measures obtained in a separate session on a different day in the other group.

Results: 

ASSR thresholds were observed in all 10 subjects at each of four frequencies and in both trials. On average, these ASSR thresholds were observed at 100 dB HL (SD = 5 dB). Because these responses were at least 18 to 22 dB below the limits of the equipment where all subjects had no behavioral responses, it is reasonable to conclude that the ASSRs were not generated by the auditory system.

Conclusions: 

An artifact or distortion may be present in the recording of ASSRs at high levels. These data bring into question the view that there is a wider dynamic range for ASSR measurements compared with auditory brain stem response measurements, at least with current implementation.

In Brief

The purpose of this study was to determine the maximum stimulus levels at which a measured auditory steady-state response (ASSR) can be assumed to be a reliable measure of auditory threshold. ASSRs were measured in 10 subjects with profound hearing loss who did not respond behaviorally at the maximum levels produced by both the pure-tone audiometers and the ASSR system. ASSRs were observed in all 10 subjects at each of four octave frequencies (0.5 to 4 kHz). On average, ASSR thresholds occurred at 100 dB HL (SD = 5 dB), which was 18–22 dB below the equipment limits at which subjects had no response. These data suggest that an artifact or distortion was present in ASSR recordings, and highlight the importance of knowing the maximum level at which a measured response can be assigned to the auditory system.