Ganzfeld Debate

The ganzfeld paradigm — a sensory-attenuation protocol for testing free-response ESP — became the most extensively contested experimental program in parapsychology between 1985 and 2013. The exchange progressed from Hyman’s 1985 critique and Honorton’s 1985 response[1][2] through the 1986 Joint Communique[3], autoganzfeld replications[4], methodological probes for acoustic leakage and experimenter effects[5][6], and successive meta-analyses[7][8][9]. This spoke documents that exchange and reassesses the often-repeated “ten years of negative ganzfeld research” framing tied to Susan Blackmore’s early dissertation work[10][11].

Key findings

  • Hyman (1985) and Honorton (1985) independently analyzed the same 28-study Honorton ganzfeld database and reached different overall conclusions about replication and methodology[1][2].
  • The 1986 Joint Communique by Hyman & Honorton specified procedural standards (randomization, security, blinding, statistical reporting) that subsequent ganzfeld work was expected to meet[3].
  • Bem & Honorton (1994) reported the PRL autoganzfeld series in Psychological Bulletin, with hit rates of about 32% against a 25% chance baseline across 354 sessions[4].
  • Wiseman, Smith & Kornbrot (1996) probed acoustic-leakage hypotheses in the PRL autoganzfeld data; Wiseman & Schlitz (1997) conducted a joint experimenter-effects study at the University of Hertfordshire[5][6].
  • Milton & Wiseman (1999) reported a null meta-analysis of 30 ganzfeld studies (1987-1997) outside the original PRL series[7]; Storm, Tressoldi & Di Risio (2010) and Storm, Tressoldi & Utts (2013) reported small positive effects under broader and stricter pooling, respectively[8][9].
  • Blackmore’s own 1987 first-person account describes one formal ganzfeld study (10 trained + 10 control participants) within a 26-month dissertation period covering ESP/memory, target materials, error patterns, children, Tarot, and OBE research[10].
  • Berger (1989) reported that across 29 Blackmore experiments (21 published), 7 produced statistically significant results, and documented discrepancies between dissertation and published reports[11].

The Hyman-Honorton exchange (1985)

In 1985, the Journal of Parapsychology published two analyses of the same database of 28 ganzfeld experiments compiled by Honorton. Ray Hyman’s “The ganzfeld psi experiment: A critical appraisal”[1] identified flaws in randomization procedures, judging protocols, multiple analysis, and statistical inference, and argued that the database did not support a claim of replicable psi. Charles Honorton’s “Meta-analysis of psi ganzfeld research: A response to Hyman”[2] performed an independent meta-analysis of the same studies, reported an overall effect that he characterized as not attributable to selective reporting or known methodological flaws, and disputed Hyman’s specific procedural criticisms.

Both papers used the same source database, the same publication venue, and overlapping statistical techniques; their headline conclusions about the database’s evidential weight nonetheless differed.

The 1986 Joint Communique

Following the 1985 exchange, Hyman and Honorton co-authored “A joint communique: The psi ganzfeld controversy” in the Journal of Parapsychology[3]. The communique acknowledged areas of agreement (presence of a non-chance effect in the existing database; need for improved methodology in future work) and disagreement (the appropriate interpretation of that effect). It specified procedural recommendations for future ganzfeld experiments: rigorous randomization, security against sensory leakage, judging blind to target identity, full reporting of all experimental conditions and analyses, and standardized statistical procedures.

Subsequent ganzfeld experiments — most notably the Princeton Psychophysical Research Laboratory (PRL) autoganzfeld series — were designed to incorporate these recommendations.

The autoganzfeld era and methodological probes

Bem & Honorton (1994) reported the PRL autoganzfeld results in Psychological Bulletin[4]. The autoganzfeld protocol automated target selection, randomization, and judging recording to remove specific procedural concerns raised in the 1985-86 exchange. Across 11 experimental series totaling 354 sessions, the reported hit rate was approximately 32% against a 25% mean chance expectation.

Two methodological probes followed. Wiseman, Smith & Kornbrot (1996) examined whether acoustic leakage from the sender’s room to the experimenter’s location could account for any portion of the autoganzfeld effect; their paper reported analyses of the PRL apparatus and recordings[5]. Wiseman & Schlitz (1997) conducted a joint experimenter-effects study at the University of Hertfordshire in which the two investigators ran the identical remote-staring protocol with the same participant pool; Schlitz’s sessions returned a positive effect and Wiseman’s sessions did not[6].

Successive meta-analyses (1999-2013)

Milton & Wiseman (1999) published a meta-analysis of 30 ganzfeld studies conducted outside the PRL series between 1987 and 1997 in Psychological Bulletin[7]. Their pooled estimate did not yield a statistically significant overall effect, and they argued that the post-Joint-Communique ganzfeld literature did not replicate the PRL autoganzfeld result.

Storm, Tressoldi & Di Risio (2010) published a meta-analysis of free-response studies (1992-2008) in Psychological Bulletin[8], reporting a small positive overall effect across the broader free-response corpus that includes ganzfeld. Storm, Tressoldi & Utts (2013) revisited the Storm et al. (2010) dataset using Bayesian and frequentist approaches and reported small positive effects under stricter pooling[9]. The Milton-Wiseman, Storm et al. 2010, and Storm et al. 2013 papers used overlapping but not identical study selection criteria and different time windows.

The “Blackmore ten years” claim reassessed

Susan Blackmore’s 1987 Skeptical Inquirer essay “The elusive open mind: Ten years of negative research in parapsychology”[10] is often cited in skeptical literature as documenting a decade of unsuccessful ganzfeld replication attempts. The essay itself describes a broader research program. In her own account, Blackmore conducted one formal ganzfeld study with 10 trained and 10 control participants. The “ten years” framing covers her broader parapsychology work — ESP and memory, target materials, error patterns, children, Tarot, and out-of-body experience (OBE) research — across her 26-month dissertation period (1976-1978) plus subsequent OBE work that she classifies as non-paranormal in nature.

The seminal 1985-86 ganzfeld literature — Hyman (1985), Honorton (1985), and the Joint Communique[1][2][3] — does not cite Blackmore as a ganzfeld experimenter or include her work in the 28-study database under analysis.

Berger (1989) in the Journal of the American Society for Psychical Research[11] conducted a critical examination of Blackmore’s psi experiments and reported that across 29 experiments (21 published), 7 produced statistically significant results. Berger documented discrepancies between Blackmore’s dissertation and her published reports of the same experiments, and observed that procedural flaws were invoked selectively (flagged when results were positive, not flagged when results were chance-level). The 7-of-29 significance count is a quantitative artifact of her published record that the 1987 essay’s “negative research” framing did not engage.

Counterarguments and Debate

Critique 1: The 1999 Milton-Wiseman null meta-analysis demonstrates that the autoganzfeld effect did not replicate post-Joint-Communique.

Skeptic source: Milton & Wiseman (1999), Psychological Bulletin[7].

Response: Storm, Tressoldi & Di Risio (2010) and Storm, Tressoldi & Utts (2013) reanalyzed the broader free-response corpus using different inclusion windows and pooling methods and reported small positive overall effects[8][9]. Bem & Honorton (1994) had previously documented the PRL autoganzfeld 354-session series with a 32% hit rate against a 25% baseline[4].

Analysis. Milton & Wiseman (1999) selected 30 studies from a 1987-1997 window outside the original PRL series; Storm, Tressoldi & Di Risio (2010) selected from a 1992-2008 window including a broader free-response corpus; Storm, Tressoldi & Utts (2013) applied stricter pooling to the Storm 2010 dataset. The three analyses report different overall estimates from overlapping but non-identical study sets, with study-selection and time-window choices accounting for a substantial portion of the divergence between the published estimates.

Critique 2: Acoustic leakage and experimenter effects can plausibly account for the autoganzfeld results without invoking psi.

Skeptic source: Wiseman, Smith & Kornbrot (1996); Wiseman & Schlitz (1997)[5][6].

Response: Bem & Honorton (1994) documented the PRL autoganzfeld procedural controls (automated target selection, soundproofed sender room, automated judging recording) designed to address sensory-leakage and experimenter-handling concerns from the 1985-86 exchange[4]. The Wiseman-Schlitz (1997) joint study reported a within-protocol divergence between the two investigators’ sessions, which Wiseman and Schlitz interpreted in different ways[6].

Analysis. Wiseman, Smith & Kornbrot (1996) report acoustic-apparatus analyses of the PRL setup; Bem & Honorton (1994) document the autoganzfeld procedural controls. The Wiseman-Schlitz (1997) joint paper reports identical-protocol sessions producing different per-experimenter results, with Wiseman emphasizing the chance-level Wiseman-conducted sessions and Schlitz emphasizing the positive Schlitz-conducted sessions in their respective subsequent writings.

Critique 3: Blackmore’s “ten years of negative ganzfeld research” demonstrates the autoganzfeld effect’s failure to replicate in independent hands.

Skeptic source: Blackmore (1987), Skeptical Inquirer[10].

Response: Blackmore’s own 1987 essay describes one formal ganzfeld study (10 trained + 10 control participants) within a 26-month dissertation period covering ESP/memory, target materials, error patterns, children, Tarot, and OBE research[10]. Berger (1989) reported that 7 of Blackmore’s 29 experiments (21 published) produced statistically significant results and documented discrepancies between her dissertation and published reports[11].

Analysis. Blackmore’s 1987 essay frames her parapsychology research as “ten years of negative research”; Berger (1989) cross-checked dissertation and published reports and reported 7 of 29 experiments produced statistically significant results. The seminal 1985-86 Hyman-Honorton ganzfeld database (28 studies) does not include Blackmore as a ganzfeld experimenter[1][2][3]. The “ten years of ganzfeld” framing and the documented single-formal-ganzfeld-study count are not numerically congruent in Blackmore’s own first-person record.

References
  1. Hyman, R. (1985). The ganzfeld psi experiment: A critical appraisal. Journal of Parapsychology, 49(1), 3-49. ↩︎
  2. Honorton, C. (1985). Meta-analysis of psi ganzfeld research: A response to Hyman. Journal of Parapsychology, 49(1), 51-91. ↩︎
  3. Hyman, R., & Honorton, C. (1986). A joint communique: The psi ganzfeld controversy. Journal of Parapsychology, 50, 351-364. ↩︎
  4. Bem, D. J., & Honorton, C. (1994). Does psi exist? Replicable evidence for an anomalous process of information transfer. Psychological Bulletin, 115(1), 4-18. https://doi.org/10.1037/0033-2909.115.1.4 ↩︎
  5. Wiseman, R., Smith, M., & Kornbrot, D. (1996). Exploring possible sender-to-experimenter acoustic leakage in the PRL autoganzfeld experiments. Journal of Parapsychology, 60, 97-128. ↩︎
  6. Wiseman, R., & Schlitz, M. (1997). Experimenter effects and the remote detection of staring. Journal of Parapsychology, 61(3), 197-208. ↩︎
  7. Milton, J., & Wiseman, R. (1999). Does psi exist? Lack of replication of an anomalous process of information transfer. Psychological Bulletin, 125(4), 387-391. ↩︎
  8. Storm, L., Tressoldi, P. E., & Di Risio, L. (2010). Meta-analysis of free-response studies, 1992-2008. Psychological Bulletin, 136(4), 471-485. https://doi.org/10.1037/a0019457 ↩︎
  9. Storm, L., Tressoldi, P. E., & Utts, J. (2013). Testing the Storm et al. (2010) meta-analysis using Bayesian and frequentist approaches. Psychological Bulletin, 139(1), 248-254. https://doi.org/10.1037/a0029506 ↩︎
  10. Blackmore, S. J. (1987). The elusive open mind: Ten years of negative research in parapsychology. Skeptical Inquirer, 11(3), 244-255. https://www.susanblackmore.uk/articles/the-elusive-open-mind-ten-years-of-negative-research-in-parapsychology/ ↩︎
  11. Berger, R. E. (1989). A critical examination of the Blackmore psi experiments. Journal of the American Society for Psychical Research, 83(2), 123-144. ↩︎

Related topics:

Skeptical critiques and debates Replication and meta-analysis debates Statistical and file-drawer critiques Replication (methods) Foundations

Last updated: 2026-05-27 22:32:44

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