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ABSTRACT: The existence of psi-anomalous processes of information transfer such as telepathy or clairvoyance-continues to be controversial. Earlier meta-analyses of studies using the ganzfeld procedure appeared to provide replicable evidence for psi (D. J. Bem & C. Honorton, 1994), but a follow-up meta-analysis of 30 more recent ganzfeld studies did not U. Milton & R. Wiseman, 1999). When 10 new studies published after the Milton-Wiseman cutoff date are added to their database, the overall ganzfeld effect again becomes significant, but the mean effect size is still smaller than those from the original studies. Ratings of all 40 studies by 3 independent raters reveal that the effect size achieved by a replication is significantly correlated with the degree to which it adhered to the standard ganzfeld protocol. Standard replications yield significant effect sizes comparable with those obtained in the past.
The term psi denotes anomalous processes of information transfer such as telepathy and other forms of extrasensory perception that are currently unexplained in terms of known physical or biological mechanisms. The question of whether psi actually exists continues to be controversial. In 1994, Bem and Honorton summarized meta-analyses of approximately 50 studies from 10 separate laboratories that appeared to provide replicable evidence for psi using an experimental protocol known as the ganzfeld procedure.
In most studies using the ganzfeld procedure, two participants-a "sender" and a "receiver"-are sequestered in separate, acoustically isolated rooms. For approximately 30 min, the sender concentrates on a randomly selected stimulus target, for example, an art print, a photograph, or a brief videotaped sequence. During the same period, the receiver is immersed in a mild form of perceptual isolation called the ganzfeld (total field) while providing a continuous verbal report of his or her ongoing thoughts, feelings, and images. At the completion of the ganzfeld period, the receiver is shown several stimuli (usually four) and, without knowing which stimulus was the target, is asked to rate the degree to which each matches the thoughts, feelings, and images 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...