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

Journal of Parapsychology, The, June, 2000 by Stefan Schmidt, Harald Walach

Thirty-five authors described their electrode paste, and apparently all of them took care to use a paste with an isotonic character. We were surprised that only two studies described whether there was a sufficient time lag between electrode placement and start of data recording. Site pretreatment was reported only in 20% of all cases and the methods were quite different. It seems that there are still different opinions and that no fixed standard exists. Climatic conditions were reported by only four researchers, and they did not meet the recommended values exactly.

All studies describe exactly which parameters they use. Tonic parameters as required for DMILS studies were calculated in 20 (50%) of the publications. Fifteen authors used NS.SCR with different thresholds ranging from 0.02-0.2 [micro]S, but a majority of 10 researchers chose 0.05[micro]S. Artifact control and correction seems to be a difficult topic within the psychophysiological community. Some researchers report that they recorded respiration for artifact control or that they conducted a movement control. But no one describes an exact procedure of how artifacts were dealt with.

The applied and published techniques in psychophysiological studies were not as homogenous as we expected. Possible reasons for this might be that EDA is very often only one in a set of psychophysiological variables and therefore the description of the procedures is short. Another reason is that only some, but not all, topics are standardized. In our opinion, there are insufficient standards for artifact control, climatic conditions in the lab, and site pretreatment. Furthermore, good publications apparently do not require details on these topics, nor do they ask for specifics on the time lag between electrode attachment and data recording.

DMILS/Remote Staring Studies Using EDA

We found 25 DMILS/Remote Staring publications (including proceedings) describing experiments using EDA as a dependent variable.

We omitted the two meta-analyses (Braud & Schlitz, 1991; Schlitz & Braud, 1997), but we kept an overview in the Journal of Scientific Exploration (Braud & Schlitz, 1989) as it described technical details on EDA recording.

Table 2 shows that the surveyed papers contain only little information of the applied EDA methodology. Only three techniques are described explicitly as SC-measurement; the use of a 0.5V constant voltage system is never mentioned. Forty-four percent (11 out of 25) used Ag/AgCl electrodes on fingers or palms; four studies describe the exact site (distal phalanges). There is only one case where some isotonic electrode paste is explicitly mentioned.

Data recording was mostly done by digital means with three publications reporting sample frequencies of only 1 Hz or 2 Hz. Eight studies describe EDA scoring in a comprehensible manner. Three of them take a sum of amplitudes of all nonspecific responses exceeding a certain threshold (see above). In four studies, a mean over all recorded data spots of the phasic component of skin resistance or conductance is calculated; in one the mean over the tonic component. Two studies also report calculation of means but do not specify whether they took the phasic or tonic component as source. It can be concluded by the description in the meta-analysis (Braud & Schlitz, 1991, p. 12) that all studies by Braud et al. up to 1991 took the phasic component. Two more studies report the use of the tonic component but do not specify the scoring. From our internal knowledge about the technical equipment in the Freiburg and Edinburgh labs we can conclude that another set of three studies which do not report scoring methods used the tonic component only.