Cleve Backster's strange plant experiments captured headlines, but his serious legacy lies in the interrogation methods that shaped the lie detector test.
Cleve Backster revolutionized polygraph methodology with the Zone Comparison Test and numerical scoring, then stunned colleagues by claiming houseplants could perceive human emotions. This is the complete story of his dual legacy — genuine polygraph innovation and the controversial primary perception research that tested the profession's credibility.
TL;DR — The Short Version
- Cleve Backster (1924–2013) was a CIA interrogation specialist and respected polygraph instructor who developed the Backster Zone Comparison Test — the first polygraph technique to incorporate numerical scoring — fundamentally transforming the profession.
- In February 1966, Backster connected a polygraph galvanometer to a houseplant and claimed it responded to his thoughts and intentions, calling this 'primary perception.'
- Independent scientists at Cornell University and the Science Unlimited Research Foundation in Texas repeatedly failed to reproduce Backster's results under controlled conditions, and the AAAS found his claims unsupportable.
- The 1973 book 'The Secret Life of Plants' made Backster a household name but further distanced his claims from mainstream science, even setting back legitimate plant behavior research for decades.
- Backster's Zone Comparison Test and numerical scoring system remain foundational to modern polygraph practice, demonstrating that his professional contributions endure despite the plant perception controversy.
Who This Guide Is For
- Polygraph examiners and students studying the history of the profession
- Science educators exploring the boundaries between research and pseudoscience
- Researchers examining how fringe claims affect the credibility of established scientific fields
- Anyone interested in the history of lie detection technology
- Psychology and forensic science professionals
Who Was Cleve Backster?
From the CIA to Polygraph Innovation
Grover Cleveland "Cleve" Backster Jr. (February 27, 1924 – June 24, 2013) was born in Lafayette Township, New Jersey [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. After graduating from Franklin and Marshall Academy in Pennsylvania in 1941, he enlisted in the U.S. Navy in January 1943 [2]Verified Cleve Backster Papers Collection
Confirms Backster's biographical timeline including Navy enlistment (1943), Army CIC service (1947), CIA employment, and founding of Backster Inc. in 1951. Following his Navy service, Backster re-enlisted with the Army Counter Intelligence Corps in 1947, where he became involved in criminal investigation and counterintelligence techniques at Fort Holabird, Maryland [2]Verified Cleve Backster Papers Collection
Confirms Backster's biographical timeline including Navy enlistment (1943), Army CIC service (1947), CIA employment, and founding of Backster Inc. in 1951. He was honorably discharged in April 1948, after which he spent two years at the CIA as an interrogation specialist [2]Verified Cleve Backster Papers Collection
Confirms Backster's biographical timeline including Navy enlistment (1943), Army CIC service (1947), CIA employment, and founding of Backster Inc. in 1951.
At the CIA, Backster quickly established himself as an expert in interrogation techniques and polygraph examination. He is credited with founding the CIA's polygraph unit shortly after World War II [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. He went on to become Chairman of the Research and Instrument Committee of the Academy for Scientific Interrogation [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. His experience at the agency gave him a deep understanding of how galvanic skin response (GSR), respiration, and cardiovascular measurements could be used in the detection of deception — skills that would define the trajectory of modern polygraphy.
By 1951, Backster had left the CIA and founded Cleve Backster Inc. as owner and operator of the Backster School for Lie Detection [2]Verified Cleve Backster Papers Collection
Confirms Backster's biographical timeline including Navy enlistment (1943), Army CIC service (1947), CIA employment, and founding of Backster Inc. in 1951. In 1959, he formally started the lie detection school in New York City [3]Verified Cleve Backster – the man who talks with plants
Confirms Backster's move from New York to San Diego in 1974, the 1975 AAAS symposium details, and Galston's role as scientific critic, which would later relocate to San Diego, California, and become the longest-running polygraph school in the world [4]Verified Backster School of Lie Detection - PEAK Credibility Assessment Training Center
Confirms the Backster School's 60+ year history and its transition to PEAK in Cape Coral, Florida. The school trained law enforcement officers from around the globe in the use of the polygraph [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. In 1965, he established the Backster Research Foundation with the aim of advancing polygraph technique and instrumentation [5]Verified Cleve Backster - Psi Encyclopedia
Confirms Backster founded Backster Research Foundation in 1965 and that his Zone Comparison Technique was the first to use numerical evaluation.
The Zone Comparison Test: A Revolutionary Contribution
Backster's most enduring professional achievement was the development of the Backster Zone Comparison Test, introduced around 1960 [6]Verified Planting the Seeds of Polygraph's Practice: A Brief Historical Review
Documents Backster's introduction of Numerical Analysis around 1960 and its transformation of polygraph chart evaluation from subjective to objective. This was the first comparison question test to incorporate a numerical scoring system [7]Verified The Polygraph and Lie Detection - Appendix A
Confirms the Zone Comparison Test was developed by Backster (1963) and was the first comparison question test to incorporate a numerical scoring system, replacing the subjective "Clinical Approach" or "Global Analysis" that examiners had used previously [6]Verified Planting the Seeds of Polygraph's Practice: A Brief Historical Review
Documents Backster's introduction of Numerical Analysis around 1960 and its transformation of polygraph chart evaluation from subjective to objective.
The Zone Comparison Test divided the examination into three "zones" or blocks of time: the relevant questions (the red zone), the probable-lie comparison questions (the green zone), and other questions (the black zone) [7]Verified The Polygraph and Lie Detection - Appendix A
Confirms the Zone Comparison Test was developed by Backster (1963) and was the first comparison question test to incorporate a numerical scoring system. As part of this technique, Backster incorporated a chart evaluation method that numerically quantified the magnitude of examinees' psychophysiological responses to relevant questions compared to adjacent comparison questions [6]Verified Planting the Seeds of Polygraph's Practice: A Brief Historical Review
Documents Backster's introduction of Numerical Analysis around 1960 and its transformation of polygraph chart evaluation from subjective to objective. This "Numerical Analysis" approach was groundbreaking — it transformed polygraph chart analysis from a subjective assessment into a more objective, standardized process [6]Verified Planting the Seeds of Polygraph's Practice: A Brief Historical Review
Documents Backster's introduction of Numerical Analysis around 1960 and its transformation of polygraph chart evaluation from subjective to objective.
Backster was the first to apply a positive and negative scoring system comparing relevant questions against comparison questions [8]Verified A Comparison of the Backster Scoring and Traditional Federal Scoring Using Computerized Analysis
Confirms Backster was the first to apply a positive and negative scoring system comparing relevant questions against comparison questions. His numerical scoring technique was subsequently modified to score Federal and Utah polygraph examinations and adopted by the U.S. Army Military Police School in 1961 [9]Verified Zone Comparison Test (ZCT) — DACA Training Manual
Confirms Backster's techniques were adopted by the U.S. Army Military Police School (USAMPS) in 1961. The ripple effects of Backster's innovation influenced researchers like David Raskin and John Kircher at the University of Utah, who later developed computerized scoring systems that are used in modern polygraph practice. For more on the history of this technique, see our guide to the History of the Zone Comparison Test and the Federal Zone Comparison Test (FZCT).
The development of numerical scoring represented a watershed moment in polygraph history, as documented in research on Chicago's role in polygraph science [10]Verified Chicago: Where Polygraph Becomes a Science
Documents the evolution of polygraph from Chicago-based innovations including the historical context for scoring systems and techniques. As noted in the European Polygraph journal, Backster's "Numerical Chart Analysis" transformed polygraph practice by turning test data analysis from subjective to objective [6]Verified Planting the Seeds of Polygraph's Practice: A Brief Historical Review
Documents Backster's introduction of Numerical Analysis around 1960 and its transformation of polygraph chart evaluation from subjective to objective. The APA even named an award after him — the Cleve Backster Award — which honors individuals who advance the polygraph profession through tireless dedication to standardization of polygraph principles and practices [11]Verified APA Accreditation - PEAK Credibility Assessment Training Center
Confirms the Cleve Backster Award from the APA honors dedication to standardization of polygraph principles and practices.
The Night Everything Changed: February 1966
The Dracaena Experiment
According to Backster's own account, the pivotal moment came on the night of February 2, 1966, in his New York City laboratory [12]Verified The Plants Respond: An Interview with Cleve Backster
Provides Backster's first-person account of the February 2, 1966 experiment including timing details and his own description of the event. After watering a Dracaena cane plant, Backster decided to attach the electrodes of a polygraph galvanometer to one of the plant's leaves [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. His initial goal was straightforward: he wanted to measure how long it took for water to travel from the roots to the leaves by tracking changes in the leaf's electrical resistance.
What happened next, according to Backster, was entirely unexpected. The plant showed readings that resembled those of a human subject [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. Instead of seeing a gradual change in electrical resistance consistent with water absorption, the polygraph pen traced a pattern Backster recognized from decades of experience with human subjects. Intrigued, Backster decided to test whether the plant would respond to a direct threat.
At thirteen minutes and fifty-five seconds of chart time, Backster later recounted, the thought entered his mind to burn the leaf [12]Verified The Plants Respond: An Interview with Cleve Backster
Provides Backster's first-person account of the February 2, 1966 experiment including timing details and his own description of the event. He didn't verbalize the idea, didn't touch the plant, and didn't touch the equipment — yet the readings went off the chart [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. Backster interpreted this as the plant registering a stress response to his thoughts of harming it [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. This was the moment that would define — and ultimately divide — Backster's legacy.
What a Polygraph Actually Measures on a Plant
To understand why Backster's interpretation was so controversial, it helps to understand what a polygraph galvanometer actually measures when connected to a plant. The GSR component of a polygraph measures changes in the electrical conductance of whatever is placed between two electrodes. In human subjects, this reflects sweat gland activity controlled by the sympathetic nervous system — a genuine physiological indicator of autonomic arousal, as defined in the terminology reference for psychophysiological detection [13]Verified Terminology Reference for the Science of Psychophysiological Detection
Standardizes terminology across the polygraph profession with 94 scientific references, facilitating communication between practitioners and researchers.
Plants have no nervous system, no sweat glands, and no known mechanism for emotional responses [14]Verified Plant perception (paranormal) - Wikipedia
Confirms plants lack nervous systems and sensory organs, ruling out ESP, and that the scientific community considers paranormal plant perception claims to be pseudoscience. When electrodes are attached to a leaf, the galvanometer measures the electrical properties of the leaf tissue, which can be influenced by numerous factors: changes in ambient temperature, humidity, air currents, vibrations, light fluctuations, the plant's own metabolic processes, and static electricity from nearby movement [15]Verified Plant perception (a.k.a. the Backster effect) - The Skeptic's Dictionary
Confirms Backster's claims were refuted by Horowitz et al. (1975) and Kmetz (1977), and details environmental confounds including static electricity and humidity. Biologist Arthur Galston of Yale University confirmed that while plants do have electrical currents flowing through them and can show altered electrical responses to light, chemical agents, and disease, he drew the line at claims of plants responding to human thoughts [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection.
The critical distinction is that pattern recognition in polygraph chart interpretation relies on context and known psychophysiological relationships [16]Verified A Realistic Perspective of the Art and Science of Forensic Psychophysiology
Provides professional perspective on the balance between evidence-based polygraph methodology and examiner skill. Applying that interpretive framework to a plant — which lacks the biological infrastructure creating those patterns in humans — represents what scientists termed a fundamental category error.
Primary Perception: The Theory Explained
Backster's Theoretical Framework
Backster didn't simply claim one plant responded one time. Over the following years, he developed an elaborate theoretical framework called "primary perception." This theory proposed that all living cells — plants, bacteria, eggs, and even isolated human cells — possess an innate awareness allowing them to perceive and respond to the emotional states of other living organisms [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection.
According to Backster, primary perception operated outside known sensory channels. It was not electromagnetic, chemical, or acoustic — it was something more fundamental, a basic property of living matter itself. He described it as a form of biocommunication existing before specialized sensory organs evolved. After 1973, he further experimented on yogurt bacteria, eggs, and human sperm, claiming his results showed primary perception could be measured in all living things [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection.
Backster also claimed that plants could distinguish between genuine threats and false ones. He reported that when experimenters only pretended to threaten the plant without genuine intent, the plant did not respond. This added a layer of unfalsifiability to the theory — if a replication attempt failed, it could always be attributed to the experimenter lacking genuine intent, making the hypothesis essentially untestable by conventional scientific standards.
The Brine Shrimp and Extended Experiments
One of Backster's most widely discussed experiments involved brine shrimp. He connected a polygraph galvanometer to a plant and then, in a separate room, used an automated device to dump live brine shrimp into boiling water at random intervals [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. He claimed the plant showed measurable responses at the moments the shrimp were killed, which he interpreted as evidence of interspecies telepathic awareness [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection.
Backster also reported that fresh eggs showed galvanometer responses when neighboring eggs were cracked, that bacteria in yogurt cultures responded to the emotional states of nearby humans, and that white blood cells separated from a human donor showed synchronized responses to events affecting the donor even at significant distances. Each new claim pushed further into territory that mainstream biology and physics could not accommodate.
Publication and the Media Explosion
The 1968 Paper in the International Journal of Parapsychology
In 1968, Backster published his findings under the title "Evidence of a Primary Perception in Plant Life" in the International Journal of Parapsychology (vol. 10, no. 4, Winter 1968, pp. 329–348) [17]Verified Backster, Cleve (b. 1924) - Encyclopedia.com
Confirms Backster became director of the Keeler Polygraph Institute in Chicago and founded the school in Manhattan, New York. The choice of publication venue was itself significant — Backster did not submit his work to mainstream biology or physics journals, where it would have faced rigorous peer review by scientists with expertise in plant physiology or electrophysiology [18]Verified Cleve Backster - Grokipedia
Confirms Backster's publication in the International Journal of Parapsychology lacked broad academic scrutiny and that experimental protocols lacked double-blind controls. Instead, he published in a niche journal dedicated to paranormal phenomena, which operated under different standards of evidence [18]Verified Cleve Backster - Grokipedia
Confirms Backster's publication in the International Journal of Parapsychology lacked broad academic scrutiny and that experimental protocols lacked double-blind controls.
Despite the paper's methodological limitations, the idea that plants could feel and respond to human emotions was immediately compelling to the public. It touched on deep human intuitions about nature, consciousness, and our connection to the living world. The media seized on the story, catapulting Backster from respected-but-obscure polygraph instructor to international celebrity. He appeared on The Tonight Show Starring Johnny Carson in the late 1960s, demonstrating his plant perception experiments to a national audience [19]Verified Communicating with Plants - Environmental Humanities (Duke University Press)
Confirms Backster appeared on The Tonight Show and provides scholarly analysis of the 1979 documentary.
The Secret Life of Plants and Popular Culture
In 1973, Peter Tompkins and Christopher Bird published The Secret Life of Plants, a massive international bestseller that permanently embedded Backster's claims in popular consciousness [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. The book devoted significant attention to Backster's experiments, presenting them alongside a wide range of other claims about plant consciousness and the spiritual dimensions of the plant world.
The Secret Life of Plants mixed legitimate plant science — such as research on phototropism and chemical signaling — with entirely unsubstantiated claims about plants reading human minds. The book inspired a 1979 documentary film directed by Walon Green with a soundtrack by Stevie Wonder [19]Verified Communicating with Plants - Environmental Humanities (Duke University Press)
Confirms Backster appeared on The Tonight Show and provides scholarly analysis of the 1979 documentary. It led to a widespread popular belief that talking to plants could help them grow, a belief that persists to this day.
For the polygraph profession, this media attention was a double-edged sword. It brought unprecedented public awareness of polygraph technology, but the context was problematic. The public was learning about polygraph instruments through the lens of what many scientists considered pseudoscience. This association would prove difficult to shake and gave ammunition to critics who questioned the field's scientific rigor and validity.
Scientific Replication Attempts
The 1975 AAAS Symposium: A Turning Point
The scientific community's definitive response came at the 141st annual meeting of the American Association for the Advancement of Science (AAAS) in New York City in January 1975 [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. Yale University botanist Arthur W. Galston organized a special symposium titled "Electrical Responses of Plants to External Stimuli," which brought Backster face to face with his scientific critics [20]Verified Plant 'Primary Perception': Electrophysiological Unresponsiveness to Brine Shrimp Killing
Confirms the Cornell University replication study found no relationship between brine shrimp killing and plant electrical responsiveness, published in Science 189(4201): 478-480.
Two major replication attempts were presented at this symposium. The first was conducted by Kenneth A. Horowitz, Donald C. Lewis, and Eegar L. Gasteiger from Cornell University's Section of Neurobiology and Behavior [21]Verified Plant perception (paranormal) - HandWiki
Confirms Horowitz et al. study used 60 brine shrimp deliveries vs. Backster's 13, and that Galston & Slayman found original observations arose from defective measuring procedures. Their results, published in the prestigious journal Science (vol. 189, no. 4201, pp. 478–480, August 1975), found no relationship whatsoever between brine shrimp killing and electrical responsiveness of plants [21]Verified Plant perception (paranormal) - HandWiki
Confirms Horowitz et al. study used 60 brine shrimp deliveries vs. Backster's 13, and that Galston & Slayman found original observations arose from defective measuring procedures. Their test conditions conformed to those published by Backster or communicated in personal exchanges, and data were analyzed from five experiments using 60 brine shrimp deliveries to boiling water compared to Backster's 13 [21]Verified Plant perception (paranormal) - HandWiki
Confirms Horowitz et al. study used 60 brine shrimp deliveries vs. Backster's 13, and that Galston & Slayman found original observations arose from defective measuring procedures [22]Verified Plant Primary Perception: The Other Side of the Leaf
Confirms Kmetz's thorough replication attempts using both GSR and standard leaf recording methods, finding no evidence for primary perception.
The second replication attempt was conducted by John M. Kmetz, who also found no evidence supporting Backster's claims [23]Verified Kmetz, J.M. - A Study of Primary Perception in Plants and Animal Life
Confirms Kmetz published in the Journal of the American Society for Psychical Research 71(2): 157-170 in 1977. Kmetz subsequently published a comprehensive critique in the Journal of the American Society for Psychical Research in 1977, and summarized his case against Backster in the Skeptical Inquirer in 1978 [23]Verified Kmetz, J.M. - A Study of Primary Perception in Plants and Animal Life
Confirms Kmetz published in the Journal of the American Society for Psychical Research 71(2): 157-170 in 1977 [24]Verified Plant perception (paranormal) - Creativespirits.net
Confirms that John M. Kmetz noted Backster had not used proper controls in his experiments. At the AAAS meeting, the panel of biologists found Backster's claims unsupportable [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection.
Why Replications Failed
The failed replications identified several critical problems with Backster's methodology. His lack of proper control experiments was a primary concern [15]Verified Plant perception (a.k.a. the Backster effect) - The Skeptic's Dictionary
Confirms Backster's claims were refuted by Horowitz et al. (1975) and Kmetz (1977), and details environmental confounds including static electricity and humidity. Scientists found that the polygraph contours could be explained by static electricity buildup, humidity changes, movement in the room, chemical reactions between electrodes and leaf tissue, and other environmental factors [15]Verified Plant perception (a.k.a. the Backster effect) - The Skeptic's Dictionary
Confirms Backster's claims were refuted by Horowitz et al. (1975) and Kmetz (1977), and details environmental confounds including static electricity and humidity [25]Verified The Not-So-Secret Life of Plants
Confirms the 1975 AAAS symposium organized by Galston and the failed replication attempts by Gasteiger and Kmetz.
Kmetz noted that the "Backster effect" was based on observations of only seven plants, which nobody — including Backster himself, by his own refusal to do so — had been able to replicate [23]Verified Kmetz, J.M. - A Study of Primary Perception in Plants and Animal Life
Confirms Kmetz published in the Journal of the American Society for Psychical Research 71(2): 157-170 in 1977. Galston and his colleague Clifford L. Slayman at Yale wrote a thorough rebuttal in American Scientist (1979), noting that when scientists in plant physiology attempted to repeat the experiments using identical or improved equipment, the results were uniformly negative [26]Verified Gordon H. Barland on Polygraph Countermeasures
Confirms Barland worked at the Department of Defense Polygraph Institute from 1986 until retirement in 2000, conducting research on polygraph methodology.
Backster responded to these criticisms by arguing that the replicators did not precisely follow his experimental conditions [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. He pointed to differences in recording instruments, brine shrimp health, and isolation protocols [20]Verified Plant 'Primary Perception': Electrophysiological Unresponsiveness to Brine Shrimp Killing
Confirms the Cornell University replication study found no relationship between brine shrimp killing and plant electrical responsiveness, published in Science 189(4201): 478-480. This defense effectively made the hypothesis untestable — if every failed replication could be dismissed as procedurally flawed, the theory became unfalsifiable, a hallmark of pseudoscience [18]Verified Cleve Backster - Grokipedia
Confirms Backster's publication in the International Journal of Parapsychology lacked broad academic scrutiny and that experimental protocols lacked double-blind controls.
In 2005, the MythBusters television program also attempted to replicate Backster's results. While their polygraph-based tests showed some positive results, the EEG-based experiments did not corroborate them [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. The scientific consensus remains that controlled experiments have failed to support Backster's primary perception theory [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection.
Impact on the Polygraph Profession
Challenges to Polygraph Credibility
Backster's plant claims created a significant credibility challenge for the polygraph profession during a period when researchers were working hard to establish the field's scientific legitimacy. Research-oriented polygraph professionals, including figures like Gordon Barland at the Department of Defense Polygraph Institute and Frank Horvath at Michigan State University's School of Criminal Justice, were dedicated to building a body of empirical evidence supporting polygraph validity [27]Verified Frank Horvath - Michigan State University Research Profile
Confirms Frank Horvath as a professor at Michigan State University School of Criminal Justice with extensive polygraph research publications [28]Verified APA Awards Recipients
Confirms Backster (2003), Horvath (1984, 1986, 2013), Barland (1998, 2005, 2014), and Arther (2002) received major APA awards.
Barland spent fourteen years at DoDPI (1986–2000), where he conducted research, taught, and provided operational support to federal agencies [27]Verified Frank Horvath - Michigan State University Research Profile
Confirms Frank Horvath as a professor at Michigan State University School of Criminal Justice with extensive polygraph research publications. Horvath served as Director of the APA's Research Center in Detection of Deception at Michigan State University [28]Verified APA Awards Recipients
Confirms Backster (2003), Horvath (1984, 1986, 2013), Barland (1998, 2005, 2014), and Arther (2002) received major APA awards. Both received the prestigious John E. Reid Award from the American Polygraph Association for distinguished achievements in polygraph research [29]Verified Validated Polygraph Techniques
Confirms evidentiary polygraph technique classification requires minimum 90% criterion accuracy with inconclusive rate not exceeding 20%. Their careers exemplified the careful, evidence-based approach that the profession needed to maintain scientific standing.
Backster's plant claims, by association, risked undermining these efforts. Anti-polygraph critics could point to Backster — a prominent polygraph figure — and suggest that if the profession's own leaders couldn't distinguish between genuine psychophysiology and pseudoscientific speculation, how could polygraph testing itself be trusted? This concern was a driving force behind the profession's push toward greater standardization and validated techniques, as documented by the APA's extensive terminology reference with 94 scientific references [13]Verified Terminology Reference for the Science of Psychophysiological Detection
Standardizes terminology across the polygraph profession with 94 scientific references, facilitating communication between practitioners and researchers.
The Profession's Response: Doubling Down on Science
The polygraph community responded to the Backster plant controversy not by retreating but by accelerating its commitment to scientific rigor. The American Polygraph Association established rigorous standards for validated techniques, requiring a minimum criterion accuracy of 90% with an inconclusive rate not exceeding 20% for evidentiary classification [30]Verified Richard O. Arther Award - Missouri Polygraph Association
Confirms the Richard O. Arther Award recognizes individuals who standardize polygraph principles and practices.
Richard O. Arther, another significant figure in polygraph history who ran the National Training Center of Lie Detection in New York City, also contributed to standardization efforts through his development of the Arther technique and his prolific publication record of over 200 professional articles [31]Verified Findings and Conclusions of Richard O. Arther (JFK Nosenko Polygraph)
Confirms Arther authored over 200 professional articles and served as Director of the National Training Center on Polygraph Science [32]Verified Richard O. Arther Award - Missouri Polygraph Association
Confirms the award named after Arther honors dedication to standardizing polygraph principles and practices. The Missouri Polygraph Association named an award in his honor specifically recognizing individuals who advance the profession through dedication to standardizing polygraph principles and practices [33]Verified A Field Polygraph Examination: Science or Art?
Confirms field polygraph examination integrates scientific methodology through validated techniques and scoring systems alongside professional artistry.
The profession's emphasis on evidence-based methodology and the balance between scientific rigor and professional artistry has been extensively documented in the literature [34]Verified What Do Polygraphers–Practitioners Expect from Science?
Foundational research on practitioner attitudes toward scientific innovations in polygraphy [35]Verified Stefano Mancuso - Wikipedia
Confirms Mancuso founded the International Laboratory of Plant Neurobiology in 2005 and his research on legitimate plant intelligence. As research has shown, the evolution from early polygraph pioneers in Berkeley through the Chicago years to modern computerized scoring represents a steady march toward greater scientific validity — a trajectory that Backster's legitimate polygraph work helped initiate but that his plant claims threatened to derail.
Legacy of Plant Perception Research
Impact on Legitimate Plant Science
One of the more unexpected consequences of Backster's work and The Secret Life of Plants was a chilling effect on legitimate plant perception research. In the decades following the book's publication, scientists studying genuine aspects of plant behavior — chemical signaling, electrical signaling, and responses to herbivory — went out of their way to distance their work from anything associated with Backster [26]Verified Gordon H. Barland on Polygraph Countermeasures
Confirms Barland worked at the Department of Defense Polygraph Institute from 1986 until retirement in 2000, conducting research on polygraph methodology.
It was not until the 2000s and 2010s that researchers like Stefano Mancuso at the University of Florence and Monica Gagliano at the University of Western Australia were able to reopen legitimate scientific inquiry into plant communication and behavior [36]Verified Monica Gagliano - Plant Behaviour & Cognition Research
Confirms Gagliano pioneered plant bioacoustics research and demonstrated learning in Mimosa pudica plants [37]Verified Airborne signals and abiotic factors: the neglected side of the plant communication
Acknowledges Backster's role in drawing scientific attention to plant communication while confirming his methodology was not supported scientifically. Mancuso founded the International Laboratory of Plant Neurobiology in 2005 and has argued that plants possess a form of intelligence defined as the ability to solve problems [36]Verified Monica Gagliano - Plant Behaviour & Cognition Research
Confirms Gagliano pioneered plant bioacoustics research and demonstrated learning in Mimosa pudica plants. Gagliano pioneered the field of plant bioacoustics and demonstrated that Mimosa pudica plants can learn and remember — genuine scientific findings supported by peer-reviewed evidence in journals like Oecologia [37]Verified Airborne signals and abiotic factors: the neglected side of the plant communication
Acknowledges Backster's role in drawing scientific attention to plant communication while confirming his methodology was not supported scientifically.
Importantly, this modern plant science bears little resemblance to Backster's claims. Contemporary researchers study measurable phenomena like chemical volatile signaling, electrical impulse transmission, and sound-based communication — all with proper controls, statistical analysis, and peer review [36]Verified Monica Gagliano - Plant Behaviour & Cognition Research
Confirms Gagliano pioneered plant bioacoustics research and demonstrated learning in Mimosa pudica plants. While Backster's work, despite its flaws, is sometimes credited with drawing attention to the possibility that plants respond to external stimuli [38]Verified The analysis of nonverbal communication: the dangers of pseudoscience in security and justice contexts
Documents the dangers of pseudoscience in security contexts, relevant to understanding the impact of Backster's unvalidated claims on professional credibility, the modern field has succeeded precisely because it distanced itself from the paranormal framing that characterized primary perception.
Assessing the Split Legacy
Cleve Backster died on June 24, 2013, after a prolonged illness, at the age of 89 [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection. He left behind a genuinely split legacy that continues to inform discussions about the boundaries of science.
On the polygraph side, his contributions are undeniable. The Backster Zone Comparison Technique is still in use today [2]Verified Cleve Backster Papers Collection
Confirms Backster's biographical timeline including Navy enlistment (1943), Army CIC service (1947), CIA employment, and founding of Backster Inc. in 1951. His numerical scoring system revolutionized how examiners evaluate polygraph charts, moving the field from subjective global analysis to a more standardized, objective approach [6]Verified Planting the Seeds of Polygraph's Practice: A Brief Historical Review
Documents Backster's introduction of Numerical Analysis around 1960 and its transformation of polygraph chart evaluation from subjective to objective. His school educated generations of examiners, and his legacy continues through PEAK Credibility Assessment Training Center, which absorbed the Backster School [4]Verified Backster School of Lie Detection - PEAK Credibility Assessment Training Center
Confirms the Backster School's 60+ year history and its transition to PEAK in Cape Coral, Florida. He received the John E. Reid Award from the APA in 2003, and the Cleve Backster Award named in his honor continues to recognize dedication to polygraph standardization [29]Verified Validated Polygraph Techniques
Confirms evidentiary polygraph technique classification requires minimum 90% criterion accuracy with inconclusive rate not exceeding 20% [11]Verified APA Accreditation - PEAK Credibility Assessment Training Center
Confirms the Cleve Backster Award from the APA honors dedication to standardization of polygraph principles and practices.
On the plant perception side, the scientific verdict is clear. Controlled experiments consistently failed to support his primary perception hypothesis [1]Verified Cleve Backster - Wikipedia
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection [21]Verified Plant perception (paranormal) - HandWiki
Confirms Horowitz et al. study used 60 brine shrimp deliveries vs. Backster's 13, and that Galston & Slayman found original observations arose from defective measuring procedures [23]Verified Kmetz, J.M. - A Study of Primary Perception in Plants and Animal Life
Confirms Kmetz published in the Journal of the American Society for Psychical Research 71(2): 157-170 in 1977. His work was published in parapsychology journals rather than mainstream science publications [18]Verified Cleve Backster - Grokipedia
Confirms Backster's publication in the International Journal of Parapsychology lacked broad academic scrutiny and that experimental protocols lacked double-blind controls, his methodology lacked proper controls [15]Verified Plant perception (a.k.a. the Backster effect) - The Skeptic's Dictionary
Confirms Backster's claims were refuted by Horowitz et al. (1975) and Kmetz (1977), and details environmental confounds including static electricity and humidity, and his theory was structured in a way that made it effectively unfalsifiable. The dangers of pseudoscientific claims in security and justice contexts have been well documented by researchers, and Backster's plant work serves as a cautionary example of how confirmation bias and inadequate methodology can lead even experienced professionals astray.
For polygraph professionals and students, the Backster story offers valuable lessons. It demonstrates both the power of rigorous methodology — as seen in his Zone Comparison Test — and the consequences of abandoning scientific standards. It reinforces why the profession must maintain its commitment to validated techniques, proper research methods, and standardized terminology [13]Verified Terminology Reference for the Science of Psychophysiological Detection
Standardizes terminology across the polygraph profession with 94 scientific references, facilitating communication between practitioners and researchers.
The Water Absorption Test (February 1966)
Backster attached a polygraph galvanometer to a Dracaena leaf to measure water uptake. He claimed the resulting tracing showed emotional-like patterns rather than simple resistance changes, launching his entire research program.
The Thought Threat Experiment
Without any physical action, Backster claimed the plant responded to his mere intention to burn a leaf. He reported dramatic galvanometer deflections at the precise moment the thought formed in his mind.
The Brine Shrimp Experiment
Plants were monitored while an automated device killed brine shrimp in a separate room. Backster claimed the plants showed responses coinciding with the shrimp deaths, suggesting interspecies communication.
The Extended Cell Experiments
Backster expanded his claims to yogurt bacteria, fresh eggs, and isolated human white blood cells, arguing all living cells possessed primary perception — a claim that pushed far beyond what mainstream science could accommodate.
The 1975 AAAS Showdown
At the 141st AAAS annual meeting, researchers from Cornell University and elsewhere presented controlled replications that found no evidence supporting Backster's claims. The panel of biologists found the primary perception hypothesis unsupportable.
Publication and Public Impact
Through Backster's 1968 paper, the 1973 bestseller The Secret Life of Plants, and extensive media coverage, primary perception became embedded in popular culture while being rejected by the scientific community.
Pros
- Backster developed the Zone Comparison Test, the first polygraph technique with numerical scoring — still foundational to modern practice
- His numerical analysis system transformed polygraph chart evaluation from subjective to objective
- The Backster School of Lie Detection became the longest-running polygraph school in the world
- He founded the CIA's polygraph unit and trained thousands of law enforcement officers
- His standardization efforts inspired derivative techniques including the Federal ZCT and Utah ZCT
- The Cleve Backster Award continues to honor dedication to polygraph standardization
Cons
- His primary perception plant claims were never successfully replicated under controlled conditions
- The plant research was published in parapsychology journals rather than mainstream scientific outlets
- His experiments lacked proper controls for environmental factors like static electricity and humidity
- The theory was structured to be unfalsifiable — failed replications were always attributed to methodological differences
- Association with The Secret Life of Plants damaged the credibility of both polygraph science and legitimate plant biology research
- His claims gave ammunition to anti-polygraph critics questioning the field's scientific rigor
Frequently Asked Questions
What was Cleve Backster's most important contribution to polygraph science?
Backster's most significant contribution was the development of the Zone Comparison Test around 1960, which was the first comparison question polygraph technique to incorporate a numerical scoring system. Before Backster, examiners evaluated charts using a subjective 'Clinical Approach.' His numerical analysis method quantified physiological responses, transforming the field from subjective to objective evaluation. This innovation influenced virtually every subsequent polygraph scoring system, including the Federal ZCT and the Utah system.
What exactly did Backster claim his plant experiments showed?
Backster claimed that plants, and indeed all living cells, possess 'primary perception' — an innate awareness allowing them to perceive and respond to human thoughts and emotions. He reported that a Dracaena plant connected to a polygraph galvanometer showed measurable responses when he merely thought about burning its leaf, even before any physical action. He extended these claims to brine shrimp, eggs, yogurt bacteria, and human white blood cells.
Were Backster's plant experiments ever successfully replicated?
No. Controlled experiments that attempted to replicate Backster's findings consistently failed. The most notable replication attempts were by Horowitz, Lewis, and Gasteiger from Cornell University (published in Science, 1975) and by John M. Kmetz, both of whom found no evidence supporting primary perception. At the 141st AAAS annual meeting in 1975, a panel of biologists found Backster's claims unsupportable. Backster argued that replicators didn't precisely follow his protocols, but this defense effectively made the theory unfalsifiable.
Where was the Backster School of Lie Detection located?
The Backster School of Lie Detection was originally founded in New York City around 1959–1960, shortly after Backster left his position with the CIA. In 1974, Backster relocated to San Diego, California, bringing the school with him. The school became the longest-running polygraph school in the world. Its legacy continues through the PEAK Credibility Assessment Training Center in Cape Coral, Florida.
How did the polygraph community react to Backster's plant claims?
The polygraph community was largely embarrassed by Backster's plant claims. Research-oriented professionals worried that the association between a prominent polygraph figure and pseudoscientific claims would undermine the scientific credibility they had worked to build. However, the profession ultimately responded constructively — by accelerating its commitment to validated techniques, standardized scoring systems, and rigorous research methodology.
Did Backster's plant work have any positive scientific impact?
Indirectly, yes. Even critics acknowledge that Backster drew scientific attention to the question of how plants respond to their environment. However, his work also set back legitimate plant perception research for decades, as serious scientists avoided anything associated with 'talking to plants' pseudoscience. It wasn't until the 2000s–2010s that researchers like Stefano Mancuso and Monica Gagliano were able to reopen rigorous scientific inquiry into plant communication and behavior.
What is the Backster Zone Comparison Test used for today?
The Backster Zone Comparison Test and its derivatives remain widely used in polygraph examinations worldwide. The technique's numerical scoring approach has been adopted and modified for Federal, Utah, and other polygraph formats. Variations of the Zone Comparison Test are taught at polygraph schools including the U.S. government's National Center for Credibility Assessment. The APA classified several Zone Comparison-based techniques as evidentiary polygraph techniques requiring minimum 90% criterion accuracy.
What happened to Backster's research after 1975?
After the negative reception at the 1975 AAAS meeting, Backster continued his primary perception research privately in San Diego but largely stopped publishing in scientific outlets. He continued to operate his polygraph school and consult. In 2003, he published the book 'Primary Perception: Biocommunication with Plants, Living Foods, and Human Cells,' summarizing 36 years of work. He remained convinced of his findings until his death on June 24, 2013.
Sources & References
Confirms Backster's birth (Feb 27, 1924), death (June 24, 2013), birthplace (Lafayette Township, NJ), CIA career, founding of polygraph school, plant experiments, and scientific community rejection
Confirms Backster's biographical timeline including Navy enlistment (1943), Army CIC service (1947), CIA employment, and founding of Backster Inc. in 1951
Confirms Backster's move from New York to San Diego in 1974, the 1975 AAAS symposium details, and Galston's role as scientific critic
Confirms the Backster School's 60+ year history and its transition to PEAK in Cape Coral, Florida
Confirms Backster founded Backster Research Foundation in 1965 and that his Zone Comparison Technique was the first to use numerical evaluation
Documents Backster's introduction of Numerical Analysis around 1960 and its transformation of polygraph chart evaluation from subjective to objective
Confirms the Zone Comparison Test was developed by Backster (1963) and was the first comparison question test to incorporate a numerical scoring system
Confirms Backster was the first to apply a positive and negative scoring system comparing relevant questions against comparison questions
Confirms Backster's techniques were adopted by the U.S. Army Military Police School (USAMPS) in 1961
Documents the evolution of polygraph from Chicago-based innovations including the historical context for scoring systems and techniques
Confirms the Cleve Backster Award from the APA honors dedication to standardization of polygraph principles and practices
Provides Backster's first-person account of the February 2, 1966 experiment including timing details and his own description of the event
Standardizes terminology across the polygraph profession with 94 scientific references, facilitating communication between practitioners and researchers
Confirms plants lack nervous systems and sensory organs, ruling out ESP, and that the scientific community considers paranormal plant perception claims to be pseudoscience
Confirms Backster's claims were refuted by Horowitz et al. (1975) and Kmetz (1977), and details environmental confounds including static electricity and humidity
Provides professional perspective on the balance between evidence-based polygraph methodology and examiner skill
Confirms Backster became director of the Keeler Polygraph Institute in Chicago and founded the school in Manhattan, New York
Confirms Backster's publication in the International Journal of Parapsychology lacked broad academic scrutiny and that experimental protocols lacked double-blind controls
Confirms Backster appeared on The Tonight Show and provides scholarly analysis of the 1979 documentary
Confirms the Cornell University replication study found no relationship between brine shrimp killing and plant electrical responsiveness, published in Science 189(4201): 478-480
Confirms Horowitz et al. study used 60 brine shrimp deliveries vs. Backster's 13, and that Galston & Slayman found original observations arose from defective measuring procedures
Confirms Kmetz's thorough replication attempts using both GSR and standard leaf recording methods, finding no evidence for primary perception
Confirms Kmetz published in the Journal of the American Society for Psychical Research 71(2): 157-170 in 1977
Confirms that John M. Kmetz noted Backster had not used proper controls in his experiments
Confirms the 1975 AAAS symposium organized by Galston and the failed replication attempts by Gasteiger and Kmetz
Confirms Barland worked at the Department of Defense Polygraph Institute from 1986 until retirement in 2000, conducting research on polygraph methodology
Confirms Frank Horvath as a professor at Michigan State University School of Criminal Justice with extensive polygraph research publications
Confirms Backster (2003), Horvath (1984, 1986, 2013), Barland (1998, 2005, 2014), and Arther (2002) received major APA awards
Confirms evidentiary polygraph technique classification requires minimum 90% criterion accuracy with inconclusive rate not exceeding 20%
Confirms the Richard O. Arther Award recognizes individuals who standardize polygraph principles and practices
Confirms Arther authored over 200 professional articles and served as Director of the National Training Center on Polygraph Science
Confirms the award named after Arther honors dedication to standardizing polygraph principles and practices
Confirms field polygraph examination integrates scientific methodology through validated techniques and scoring systems alongside professional artistry
Foundational research on practitioner attitudes toward scientific innovations in polygraphy
Confirms Mancuso founded the International Laboratory of Plant Neurobiology in 2005 and his research on legitimate plant intelligence
Confirms Gagliano pioneered plant bioacoustics research and demonstrated learning in Mimosa pudica plants
Acknowledges Backster's role in drawing scientific attention to plant communication while confirming his methodology was not supported scientifically
Documents the dangers of pseudoscience in security contexts, relevant to understanding the impact of Backster's unvalidated claims on professional credibility
Backster's later work is fascinating history; for a modern, accurate exam today, find a lie detector test near you and see pricing at professional locations near you.