Quantification of the auditory evoked brainstem potential using a correlation procedure

Abstract

In clinical audiology there is a need for methods of assessing auditory function which are both quantitative as well as objective, and it is with these goals in mind that we have been studying the group of brainstem potentials evoked by auditory stimulation. One parameter which is much used in traditional subjective audiometry is threshold of hearing and in recent years the relationship between subjective threshold and the thresholds of the various auditory evoked potentials have been the subject of much scrutiny. A major problem in evoked potential audiometry is identifying near-threshold responses, particularly in the usual context of relatively large background EEG noise which results in a highly variable response pattern. However, evidence is accumulating that this variability can itself be used as a parameter of the response¹ The concept can be demonstrated with the aid of Figure 1. A typical averaged response evoked by a high level stimulus in a normal hearing subject has been divided into four subaverages. At many corresponding points in the post-stimulus interval clear constraints in the amplitude values in each of the subaverages can be seen. This contrasts with the high variability of corresponding pomts in the pre-stimulus period. Therefore in these two extreme conditions, which are in effect supra-threshold and sub-threshold conditions respectively, there is a marked difference in the variability of the response pattern.