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Objective: Objective threshold estimation is possible using statistics such as magnitude-squared coherence (MSC) and responses such as the 40-Hz auditory evoked potential (AEP). The purpose of this paper is to compare three general methods of threshold estimation using MSC., Design: Using 500-Hz amplitude-modulated tones and 40-Hz AEPs from 10 paid-volunteer young adults with normal hearing, we compared three MSC-based threshold estimation methods--extrapolation, intensity series, and adaptive., Results: The extrapolation method yielded low thresholds but unacceptable variability. The intensity series method was insensitive and time-consuming. Two adaptive methods displayed good performance in terms of precision and sensitivity. The first employed an MSC criterion with a 13.5% false positive rate (per trial), but achieved overall false positive rates under 5% after 5 to 7 runs, requiring 30 to 40 minutes test time (a run is a single set of ascending or descending trials, terminated by a reversal). The second, which performed better overall, included only a single run, but collected more data at intensities near threshold than at higher intensities; test time could be further reduced (from 22 to 18 minutes) by using a stopping rule based on initial MSC and noise power estimates at each test intensity. If speed is paramount, a simple single-run method achieved threshold estimates in about 9 minutes, starting at 40 dB nHL, with acceptable precision but less sensitivity., Conclusions: A single-run adaptive method, with or without collection of additional data near threshold, yielded the best results, in terms of statistical performance and data collection time.

Magnitude squared coherence is a method of auditory evoked potential (AEP) frequency-domain analysis, measuring the degree to which the AEP is determined by the stimulus as a function of frequency. In 10 normal-hearing human subjects, scalp responses to an amplitude-modulated (AM) tone (500 Hz carrier modulated with a 40 Hz envelope) were recorded. Critical value criteria were utilized in the statistical analysis of coherence-intensity functions for determination of threshold responses. When compared with subjective determination of AEP threshold from time-domain waveforms, coherence analysis provided a significantly (p less than 0.001) more sensitive threshold measure. Coherence analysis provides information on the spectral content of the response, and allows for the objective determination of threshold which may potentially be utilized in a more expeditious threshold measurement scheme.

Sixteen normal-hearing adults were tested in both awake and sedated states for several evoked responses to low-frequency stimuli. Responses obtained by cross-correlation function, middle latency responses, and the 40-Hz response proved most sensitive; all had mean thresholds of less than 20 dB normal hearing level for the awake-alert state, but 40-Hz and middle latency response mean thresholds were shifted about 10 dB under sedation. The cross-correlation method seems to offer promise for pediatric auditory assessment.