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Measurement of Cortical Evoked Potentials by Decomposition of Their Wave Form


  Evoked potentials are used for measurement of dynamic events in the nervous system that accompany and are related to defined sequences of behavior. The usual raw data are recordings of potential differences in or around the central nervous system that fluctuate in amplitude over limited time spans during behavior. The purpose of the study is to detect, describe and classify particular states of the brain that underlie normal and abnormal patterns of behavior, especially those involving higher functions such as perception, learning, cognition, and so forth. The basic approach is to measure the recordings of the potential differences in order to express the information in them by sets of numbers. Description, classification, comparison, correlation, etc., by a variety of statistical techniques are all based on the numbers.

  This review is concerned with how the information in recordings is converted into numbers. It is assumed that the reader has already defined and measured an appropriate sensory, motor, perceptual or other behavioral event, that he or she has carried out the preliminary experiments needed optimally to observe and record event-related potentials (ERPs) generated by the brain, eyes, muscles, skin, nerves, etc. (Barlow, 1973), and that he or she is familiar with the techniques for sampling (Lopes da Silva, 1976) and digitizing (Walter, 1972) bioelectrical phenomena. The first section contains a brief statement of the main elements of theory that underlie the measurement of ERPs, and the second section describes three general systems of measurement. The third section outlines some procedures that are useful in decomposing ERPs in various ways, in order to construct and evaluate particular systems for measurement.

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