Measures for the optimum estimation of audiometric thresholds from the auditory brainstem response potentials

Auditory brainstem response potentials were recorded from normally hearing subjects using a wide range of stimulus intensities including a below-threshold condition. Various measures, including the traditional Jewett V (JV) amplitude, were taken from the recordings. The probability of incorrectly concluding that a response was present was found by analysing the distribution of the JV amplitude in the no-stimulus recordings and setting an amplitude of 100 nV as the criterion of whether or not a response is deemed to be present. This probability was used to define equivalent criteria for the other measures and evoked potential (EP) thresholds could then be found for each subject and stimulus by finding the lowest stimulus intensity at which the value of the measure being considered was at or above this criterion value. Two measures were found to give significantly lower and less variable EP thresholds than the others; JV amplitude taking into account the JV latency and a self-template measure involving the correlation between the response waveforms at a high stimulus intensity level and the test intensity level. The latter measure indicates that a template-matching method of threshold estimation might be as reliable for this purpose as the measurement of JV amplitude and has the potential diagnostic advantage over JV measurements that it could be readily used with a fully objective automatic threshold evaluation protocol. The probability of making a false-positive error was found to be disconcertingly high at 0.5 for single measures and 0.22 for complex measures. This underlines the need for replicates to be taken as this dramatically reduces the probability of large errors in threshold estimation.