Analysis of Evoked and Ongoing Electrical Activity at the Scalp of Human Subjects

Publisher Website
Google Scholar
Abstract
Electrical activity at two locations on the scalp (Vertex and Vertex-3 cm, midline) for an experimental design suitable to clinical application, was recorded on magnetic tape. Data from 5 subjects with normal hearing, for 3 testing days, were processed. Average evoked responses to bursts of wide-band noise (30 dB and 50 dB SL) for two conditions (“eyes closed” and “reading”) were computed. The ongoing background activity was processed by computing its interval histogram. The percentage of ongoing activity within the frequency range 1.5 cps to 17 cps was extracted, and the magnitude of the N1-P2 component of average responses was measured. These measures at the two electrode sites were analyzed by calculating analyses of variance for each of the four sets of data. Percentage of low-frequency background activity and N1-P2 magnitude were positively related only for Day 1. A strong habituation effect appeared for Day 2 and Day 3. Habituation reduced differences between the two conditions and also differences between the two signal strengths for the average responses. Maximum N1-P2 magnitude should be recorded for a single test with the subject relaxed and with his “eyes closed.” For repeated testing a discrimination between signals should be required to offset the attenuation of responses by habituation.

This publication has 1 reference indexed in Scilit: