Electrode Placement and Mode of Recording (Differential vs. Single-Ended) Effects on the Early Auditory-Evoked Response

Abstract

The effects of electrode placement and mode of recording (single-ended vs. differential) on latencies and amplitudes of the early auditory-evoked response were studied. The following electrode arrays were evaluated (1) vertex-neck, (2) forehead-ear canal (Enhancer I), and (3) vertex-nape. Responses were obtained on 10 normally hearing subjects at sensation levels (SLs) ranging from 15 to 75 dB. Test-retest reliability was excellent for absolute and interwave latencies for all conditions. The reliability of absolute amplitude was poor, and the stability of the amplitude ratios between waves I and V was even worse. No consistent absolute or interwave latency differences were found among electrode montages. The amplitude data suggest that the forehead-ear canal montage is preferred for differential diagnosis because it enhances the probability of detecting wave I. The electrophysiologic threshold for wave I was 5–10 dB lower with the Enhancer I. However, the vertex-neck and vertex-nape combinations are best for estimating auditory sensitivity because they gave the largest wave V amplitudes and 10–dB lower electrophysiologic thresholds. Although the differential vertex-neck and single-ended vertex-nape recordings yielded comparable results, the single-ended montage employs only two electrodes and the test leads do not require rearrangement when the test ear changes.

Key Words:

• Early auditory-evoked response
• Electrode placement
• Electrode placement reliability
• Single-ended recording
• Differential recording