There are now reports of experimental evidence consistent with these anecdotal observations. For example, several laboratory investigators have reported that meditation facilitates psi performance (Honorton, 1977). A meta-analysis of 25 experiments on hypnosis and psi conducted between 1945 and 1981 in 10 different laboratories suggests that hypnotic induction may also facilitate psi performance (Schechter, 1984). And dream-mediated psi was reported in a series of experiments conducted at Maimonides Medical Center in New York and published between 1966 and 1972 (Child, 1985; Ullman, Krippner, &h; Vaughan, 1973).
In the Maimonides dream studies, two subjects-a "receiver" and a "sender"-spent the night in a sleep laboratory. The receiver's brainwaves and eye movements were monitored as he or she slept in an isolated room. When the receiver entered a period of REM sleep, the experimenter pressed a buzzer that signaled the sender-under the supervision of a second experimenter-to begin a sending period. The sender would then concentrate on a randomly chosen picture (the "target") with the goal of influencing the content of the receiver's dream.
Toward the end of the REM period, the receiver was awakened and asked to describe any dream just experienced. This procedure was repeated throughout the night with the same target. A transcription of the receiver's dream reports was given to outside judges who blindly rated the similarity of the night's dreams to several pictures, including the target. In some studies, similarity ratings were also obtained from the receivers themselves. Across several variations of the procedure, dreams were judged to be significantly more similar to the target pictures than to the control pictures in the judging sets (failures to replicate the Maimonides results were also reviewed by Child, 1985).
These several lines of evidence suggested a working model of psi in which psi-mediated information is conceptualized as a weak signal that is normally masked by internal somatic and external sensory "noise." By reducing ordinary sensory input, these diverse psi-conducive states are presumed to raise the signal-to- noise ratio, thereby enhancing a person's ability to detect the psi-mediated information (Honorton, 1969, 1977). To test the hypothesis that a reduction of sensory input itself facilitates psi performance, investigators turned to the ganzfeld procedure (Braud, Wood, &h; Braud, 1975; Honorton &h; Harper, 1974; Parker, 1975), a procedure originally introduced into experimental psychology during the 1930s to test propositions derived from Gestalt theory (Avant, 1965; Metzger, 1930).
Like the dream studies, the psi ganzfeld procedure has most often been used to test for telepathic communication between a sender and a receiver. The receiver is placed in a reclining chair in an acoustically-isolated room. Translucent ping-pong ball halves are taped over the eyes and headphones are placed over the ears; a red floodlight directed toward the eyes produces an undifferentiated visual field and white noise played through the headphones produces an analogous auditory field. It is this homogeneous perceptual environment that is called the Ganzfeld ("total field"). To reduce internal somatic "noise," the receiver typically also undergoes a series of progressive relaxation exercises at the beginning of the ganzfeld period.
The sender is sequestered in a separate acoustically isolated room, and a visual stimulus (art print, photograph, or brief videotaped sequence) is randomly selected from a large pool of such stimuli to serve as the target for the session. While the sender concentrates on the target, the receiver provides a continuous verbal report of his or her ongoing imagery and mentation, usually for about 30 minutes. At the completion of the ganzfeld period, the receiver is presented with several stimuli (usually four) and, without knowing which stimulus was the target, is asked to rate the degree to which each matches the imagery and mentation experienced during the ganzfeld period. If the receiver assigns the highest rating to the target stimulus, it is scored as a "hit." Thus, if the experiment uses judging sets containing four stimuli (the target and three decoys or control stimuli), the hit rate expected by chance is .25. The ratings can also be analyzed in other ways; for example, they can be converted to ranks or standardized scores within each set and analyzed parametrically across sessions. And, as with the dream studies, the similarity ratings can also be made by outside judges using transcripts of the receiver's mentation report.
