Electrodermal Activity : State-Of-The-Art Measurement And Techniques For Parapsychological Purposes

We thank all the researchers who helped us understanding psychophysiological principles and spent their time debating the subject with us. We are especially grateful to Dr. Florian Schaefer, Dr. Jiri Wackermann, PD Dr. Martin Peper, and Prof. Dr. Jochen Fahrenberg, who also helped us a lot with the literature. This work is funded by the Institut Fur Grenzgebiete der Psychologie und Psychohygiene, Freiburg.

ABSTRACT: There is an ongoing trend in the last 20 years of parapsychological research of looking for evidence of psi using psychophysiological variables, and electrodermal activity (EDA) seems to be the most promising indicator for that purpose. EDA is an important psychophysiological variable for mapping subjects' arousal by monitoring the autonomic nervous system. With ongoing positive results in meta-analyses of DMILS/Remote Staring experiments, parapsychological studies using EDA as a dependent variable also becomes attractive for mainstream scientists. But to get benefits from such an exchange, it is necessary to use a state-of-the-art methodology of EDA.

This is why we studied EDA-related literature and contacted some of the leading psychophysiological labs in Germany to debate critical topics of EDA measurement. We also checked the Methods section of all studies using EDA published from 1995 to 1999 in the leading psychophysiological journals. In addition, we surveyed all DMILS/Remote Staring articles to find out whether parapsychologists use these standards.

For a good EDA measurement, psychophysiologists recommend using silver/silverchloride electrodes. They are attached to the skin by double-sided adhesive collars; possible electrode sites are on the palms or fingers. The electrodes have to be filled with a special isotonic EDA electrode paste to minimize interactions between skin and electrolyte. Electrodes used in the past for EKG, EEC, or EMG are not suitable. The time period between electrode placement and recording should be at least 15-20 mm. Temperature at the laboratory should not be less than 23[degrees] C (73.40[degrees] F) and a humidity of 50% is recommended. If EDA is applied as a dependent variable, measurement of skin conductance (SC-) is the appropriate technique. Therefore, a constant voltage (0.5V is recommended) must be applied to the electrodes while the change in the electric current flow is being measured. A tonic (level, SCL) and aphasic (response, SCR) signal can be derived from the data. Splitting the signal into these components has t o be treated by a time constant of 10 sec. After the signal is digitized it can be sampled on a hard disk; a sampling rate of 15-20 Hz is sufficient. The signal now can be scored and checked for artefacts. Scoring depends on research interest. For DMILS/Remote Staring, only tonic parameters are necessary. There are three different tonic parameters: (a) electrodermal level (mean SCL in a certain time period), (b) NS.SGR-freq (Number of nonspecific SC-responses in a certain time period; a threshold has to be defined for this parameter) and (c) sum of all amplitudes of NS.SCR.freq.

An overview of 39 recent psychophysiological studies published in Psychophysiology and International Journal of Psychaphysiology shows that almost all researchers stick to the most important standards that were published in 1981. Different or only little information has been found on topics like climatic conditions, site pretreatment, and artifact control. Most DMILS/Remote Staring studies do not meet the standards published in 1981. Important information on the applied measurement principles, electrode paste, and scoring procedures are missing in the articles. We recommend an improved methodology described and explained in the paper and more detailed descriptions within articles.

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