Physiological methods have become popular recently in psi research. In particular, measurement of skin conductance was applied successfully for the detection of presentiment, that is, precognitive response to its eliciting stimulus (Bierman & Radin, 1997; for a summary of the early work see Radin, 1997). The technology of automated stimu lus presentation as well as conductance measurement and recording is now mature enough for a sound and generally acceptable methodology.
In the 1960s I conducted an experiment for the detection of a simple telepathic message between a sender and a receiver, in which a conditioned galvanic skin response was measured. An extended abstract of that experiment appeared in The Journal of Parapsychology about a decade later (Vassy, 1978). Because recording equipment was lacking, all data were obtained by human observation, which was cumbersome and prone to errors. So although the results were significantly positive, the method did not seem to be appropriate at that time. Nowadays, however, with the newly established methodology of skin conductance measurement, the weaknesses of that procedure hopefully can be eliminated. The aim of the experiment reported here was to investigate the adequacy of the method both for detecting telepathy and for asking some specific questions about its nature.
GENERAL EXPERIMENTAL DESIGN
In this paper a series of three experiments will be reported; however, they all share many common elements. In this section those aspects will be highlighted.
Basic Idea and Notation
We began by assuming that telepathy involves an as yet unidentified physiological process in the brain of the receiver. This assumption is plausible because the reception of the telepathic information is connected to a behavioral output, which obviously involves a physiological process. In these experiments, that process was used for detecting the reception of the telepathic message. We assumed further that the receiver's physiological process can be used as a conditioned stimulus in the paradigm of classical conditioning. This paradigm allows for a conditioned response upon the reception of telepathic information. In classical experiments, one must remove an unconditioned stimulus from time to time in order to recognize the conditioned response. In the experiments described in this paper, we were able to time shift the conditioning stimulus to always occur before an unconditioned stimulus, so the above requirement was not necessary here. The dependent variable throughout these studies was skin conductance.
We used a mild electric shock that was administered to two of the receivers as an unconditioned stimulus. As is well known in experimental psychology (Woodworth & Schlosberg, 1961), electric shocks cause a sudden rise in skin conductance. The skin conductance response (i.e., unconditioned response) to electric shock stimuli does not habituate, even after many trials. This is contrary to the responses to gentler emotional photographic stimuli, which have been used in "presentiment" studies. Thus, electric shocks seemed a more likely candidate for unconditioned stimuli.
Expanding upon the idea above, the conditioned stimulus was the reception of a putative telepathic message from the sender. That is, during an experimental session, a trigger signal was presented to a sender at random times. In turn, the sender was instructed to forward the warning telepathically to the receiver. After a constant delay time, a shock was presented to the receiver.
Clearly, we could detect the unconditioned skin conductance response (i.e., to the shock). We hoped that we would also detect the conditioned response in advance of the unconditioned shock stimulus. The time interval between the conditioned and the unconditioned stimulus was set to be longer than the latency time of the skin response, so the conditioned response could appear before the unconditioned stimulus. …