Technical note: A caution regarding the Knowles apparatus for psi dexterity

Journal/Book: J Parapsychol. 1996; 60: PO Box 6847, College Station, Durham, NC 27708. Parapsychology Press. 251-256.

Abstract: In a 1967 study, E.A.G. Knowles used an apparatus consisting of an opaque bulb attached to a length of glass tubing, into which were rolled a number of steel balls, half natural silver, the other half blackened over a flame, in an attempt to produce either a perfect separation or a perfect alternation of the two colors. Because one particular outcome seemed to be occurring more frequently, regardless of the subjects' aim, I suspected bias in the device. I therefore carried out 2000 control trials. It was clear that the effect of blackening the ball bearings was to retard their exit into the glass tubing. I concluded that this apparatus produces biased outcomes and is therefore not suitable for testing psi.

Note: Article Thalbourne MA, Univ Adelaide, Dept Psychol, Adelaide, SA 5005, AUSTRALIA

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