Studies
The Pearce-Pratt Distance Series
Also Known As The Duke distance experiments
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This is the single most heavily cited experiment in the history of parapsychology and the one its critics have worked hardest to dismantle. Its design was a direct answer to the complaints levelled at the earlier Duke card work: the experimenter could not see the subject, the subject could not see the cards, and neither record could be adjusted once the other was known. Because everything hung on physical separation, the criticism that followed has concerned physical separation, and specifically whether the buildings permitted an ordinary line of sight that the investigators did not consider. The figures given here are those the investigators published, and they have not been shown to be miscounted; what remains disputed is what produced them.
Facts
Disputed
Principal CriticC. E. M. Hansel, who examined the Duke buildings and argued the layout left a route by which the subject could have observed the target cards 2 C. E. M. Hansel, in ESP: A Scientific Evaluation (1966), examined the Duke University buildings in which J. Gaither Pratt recorded and J. B. Rhine supervised the Pearce-Pratt distance series, sender and subject seated in separate buildings at a distance, and argued the layout left a route by which the subject, Hubert Pearce, could in principle have observed the target cards rather than perceived them extrasensorially. Rhine and Pratt disputed both the sightlines Hansel reconstructed and the timing of the sessions relative to any such route. Hansel's method was a physical inspection of the buildings conducted years after the original 1930s sessions, working from testimony and floor plans rather than direct observation of the experiments themselves. The buildings have since been altered, so the sightline question cannot now be settled by a fresh inspection, which is why the principal critique remains a documented dispute between Hansel and the original investigators rather than a point either side's physical evidence can still resolve. Sample SizeOne subject; 1,850 trials reported across the subseries, with 558 hits against a chance expectation of 370 1 J. Gaither Pratt recorded and J. B. Rhine supervised the Pearce-Pratt distance series at Duke University, testing a single subject, Hubert Pearce, across 1,850 trials reported in the published subseries, with 558 hits against a chance expectation of 370. Rhine and Pratt's own 1954 review, A Review of the Pearce-Pratt Distance Series of ESP Tests, is the source of these figures, and they have not been shown to be miscounted by any later reanalysis. What is disputed is not the count but what produced it: the buildings in which sender and receiver sat at a distance have since been altered, so the sightline and timing questions critics raised cannot now be settled by physical inspection of the original rooms. The method available to a modern reader is documentary, comparing the investigators' own procedural description against the layout critics reconstructed from later testimony, and because the physical evidence no longer exists to check either account against, the sample size stands as reported while its interpretation remains debated. Open Questions
DesignWhether the layout of the Duke buildings during the sessions left a route by which the subject could have observed the target cards is not established. C. E. M. Hansel examined the buildings in the 1960s and argued that it did; Rhine and Pratt disputed the sightlines, the timing, and whether such an absence would have gone unnoticed. 2 Recorded as unknown rather than debated, because neither side produced the evidence that would decide it and neither conceded. The buildings have since been altered, so the question can no longer be settled by inspection. The original architectural plans of the Social Sciences building and the campus library as they stood in 1933 and 1934, with any contemporaneous record of the subject's whereabouts during the sessions, would settle it and have not been examined. Method
InvestigatorsJ. Gaither Pratt as recording experimenter and J. B. Rhine as supervisor; the subject was Hubert Pearce 1 Taken from the study's own record of who conducted it. Evidence
Replication StatusNever replicated, and the result rests on one subject whose scoring later fell to chance. C. E. M. Hansel argued that the building layout left a route by which Pearce could have observed the cards; Rhine and Pratt rejected the reconstruction in detail. The dispute is unsettled. 1 The study's replication record as reported in the literature. Where replication failed or is disputed, that is stated rather than softened. Learn More
Two Buildings, One Clock, and a Sealed Record
The arrangement was simple enough to describe in a sentence and that is the point of it. J. Gaither Pratt sat in the Social Sciences building with a shuffled deck and turned one card face down at each minute by an agreed clock. Hubert Pearce sat in the campus library, a hundred yards or more away with buildings between, wrote his call for each minute, and sealed his record. Pratt sealed his own list of the actual order. Neither man saw the other's record until both were opened in front of J. B. Rhine.
The design removes several things at once. There is no experimenter in the room to signal, deliberately or otherwise. There is no possibility of the subject seeing a card, since the cards were face down in another building. There is no opportunity to adjust either record afterwards, because both were sealed before either was read. Across the subseries the investigators reported 558 hits in 1,850 trials against a chance expectation of 370. Those figures are the investigators' own and have never been shown to be miscounted; what is disputed is whether the arrangement was as sealed as the description makes it sound. The precaution of sealing both records before either was opened is the part most often left out of secondhand accounts, and it is the part that makes the design worth arguing about at all.
Hansel's Reconstruction, and Why the Argument Is About Architecture
Thirty years later the psychologist C. E. M. Hansel visited Duke, examined the buildings and produced the criticism that has dominated discussion of the series ever since. His argument was not that Pearce had cheated but that the design did not make cheating impossible, and in an experiment offering a conclusion this large that distinction matters. Pearce was unobserved in the library for the duration of each session. Hansel argued that he could have walked to the building where Pratt was working and observed the cards from outside the room, and he specified how, drawing on the layout of doors and the position of the desk.
Rhine and Pratt replied in detail, disputing the sightlines and the timing and pointing out that Pearce would have had to be absent from the library without anyone noticing. Neither side conceded and the buildings have since been altered. What makes this exchange worth recording is the shape of it. Both parties agree the arithmetic is correct and both agree the result is decisive if the separation held, so the entire weight of one of the most cited experiments in the field rests on a question about a doorway. The general lesson, that a control which depends on nobody having checked an unobserved person is not a control, was absorbed into later protocol design.
Cross-Tradition Connections
Associated With
1933, Years The Pearce-Pratt Distance Series, an experimental series, is dated here from 1933 to 1934. Whether a single subject could name cards being turned at agreed one-minute intervals by an experimenter in a different building.
1934, Years The Pearce-Pratt Distance Series ran to 1934, having begun in 1933.
The sole experimental subject; the series is named for him and for the experimenter. A single-subject result, which is itself a limitation of the study.
Conducted By
The recording experimenter, who turned the cards in the Social Sciences building. Documented in the 1954 review of the series.
Derived From
Designed to answer the sensory-cue and recording objections raised against the earlier Duke card work. Documented in the investigators' own account of why the design was changed.
Product Of
Conducted on the Duke campus by the laboratory's own staff. Institutional record.
Sources
Open Questions (1 open question)
Did the physical layout of the Duke buildings permit Hubert Pearce to observe the target cards during the Pearce-Pratt distance series?
C. E. M. Hansel examined the buildings in the 1960s and argued that a route existed by which the subject, unobserved in the library, could have reached a position from which the cards were visible. Rhine and Pratt disputed the sightlines, the timing, and whether such an absence would have gone unnoticed. Neither side conceded, and the buildings have since been altered, so the question can no longer be settled by inspection.
What would resolve this Original architectural plans of the Social Sciences building and the campus library as they stood in 1933 and 1934, together with any contemporaneous record of Pearce's whereabouts during the sessions.
History of science; architectural history; archival research at Duke UniversityC. E. M. Hansel, ESP: A Scientific Evaluation
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