Feasibility of Diagnosing Dead Regions Using Auditory Steady-State Responses to an Exponentially Amplitude Modulated...

The aim of this study was to assess feasibility of using electrophysiological auditory steady-state response (ASSR) masking for detecting dead regions (DRs). Fifteen normally hearing adults were tested using behavioral and electrophysiological tasks. In the electrophysiological task, ASSRs were recorded to a 2 kHz exponentially amplitude-modulated tone (AM2) presented within a notched threshold equalizing noise (TEN) whose center frequency (CF_NOTCH) varied. We hypothesized that, in the absence of DRs, ASSR amplitudes would be largest for CF_NOTCH at/or near the signal frequency. In the presence of a DR at the signal frequency, the largest ASSR amplitude would occur at a frequency (f) far away from the signal frequency. The AM2 and the TEN were presented at 60 and 75 dB SPL, respectively. In the behavioral task, for the same maskers as above, the masker level at which an AM and a pure tone could just be distinguished, denoted AM2ML, was determined, for low (10 dB above absolute AM2 threshold) and high (60 dB SPL) signal levels. We also hypothesized that the value of f would be similar for both techniques. The ASSR f values obtained from grand average ASSR amplitudes, but not from individual amplitudes, were consistent with our hypotheses. The agreement between the behavioral f and ASSR f was poor. The within-session ASSR-amplitude repeatability was good for AM2 alone, but poor for AM2 in notched TEN. The ASSR-amplitude variability between and within participants seems to be a major roadblock to developing our approach into an effective DR detection method.