Exploring Possible Sender-to-Experimenter Acoustic Leakage in the PRL Autoganzfeld Experiments

Article excerpt

Bem and Honorton (1994) have recently presented data that appear to support the existence of psi. These data are based on a set of parapsychology experiments known as the ganzfeld studies. The initial section of Bern and Honorton's paper summarized a debate between skeptical psychologist Ray Hyman and parapsychologist Charles Honorton (Honorton, 1985; Hyman, 1985). This debate centered around meta-analyses of 42 ganzfeld studies that had been published up until the mid-1980s. Hyman argued that these studies did not constitute evidence for psi. Honorton argued. the opposite. Following this debate, Hyman and Honorton coauthored a "joint communique" (Hyman & Honorton, 1986), in which they set out their main areas of agreement and disagreement. They noted:

We continue to differ over the degree to which the effect constitutes evidence for psi, but we agree that the final verdict awaits the outcome of future experiments conducted by a broader range of investigators and according to more stringent standards. (p. 351)

Hyman and Honorton then outlined these stringent standards, describing methodological and reporting recommendations for future ganzfeld studies. Several leading parapsychologists commented favorably on these recommendations (see the invited commentaries directly following Hyman & Honorton, 1986).

Bem and Honorton then discussed a later set of semi-automated ganzfeld experiments (the "autoganzfeld studies"). These studies were designed to overcome the methodological problems identified in the joint communique and were originally reported in a major parapsychological journal (Honorton et al., 1990). Hyman (1994) was asked to comment on the procedure and results of Honorton's autoganzfeld studies. Hyman commended "Honorton and his colleagues (1990) for creating a protocol that eliminates most of the flaws that plagued the original ganzfeld experiments" (p. 19), but he (1) noted that the results of the studies were inconsistent with the previous ganzfeld database and (2) challenged the adequacy of the randomization procedure used in the experiment. Bem (1994) argued against both of these notions.

The paper we now present provides an in-depth analysis of one non-psi hypothesis that could potentially account for the autoganzfeld results.

A BRIEF DESCRIPTION OF THE AUTOGANZFELD STUDIES

The autoganzfeld studies were designed and run by Charles Honorton and his colleagues at the Psychophysical Research Laboratories (PRL) in Princeton, New Jersey. The autoganzfeld procedure commonly used two participants, a "sender" and a "receiver." These individuals were placed in two separate rooms. The receiver was placed in a state of mild sensory deprivation. Many parapsychologists believe that if psi exists at all it is likely to be a weak signal that is easily masked by internal somatic and external sensory noise (see, e.g., Honorton, 1977). For this reason steps were taken to help the receiver minimize the effects of such noise. They consisted of having the receiver place ping-pong ball halves over his or her eyes and then bathing them in red light. This procedure has the effect of creating a homogeneous visual field. In addition, the receiver also heard white noise through headphones, creating an undifferentiated auditory field. Finally, the receiver usually engaged in some form of relaxation exercise to minimize any somatic interference. Once the receiver was in this state, the sender was repeatedly shown a video clip that had been randomly selected from a pool of 160 clips. The sender had been asked to psychically send this clip to the receiver. The receiver was asked to report all the ideas, images, and impressions that came into his or her mind (referred to as "mentation") during this sending period. Both the experimenter and the sender could hear the receiver's comments through headphones.

The receiver was then presented with a randomly ordered "target set," consisting of four video clips (the actual target and three decoys) and was asked to rate the amount of correspondence between his or her mentation and each of these clips. …

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