The inner life
Sensory Leakage
Direct answer
Sensory Leakage: Sensory leakage is the term for information reaching the subject of a psychic experiment through the ordinary senses, by sight, sound or touch, without anyone meaning to pass it.
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At a glance
- Also called
- sensory cues esp, unconscious cues
- Found in
- Consciousness & Spiritual Psychology
- Related
- Ganzfeld Experiment, Zener Cards, Extrasensory Perception, Parapsychology
Sensory leakage is the term for information reaching the subject of a psychic experiment through the ordinary senses, by sight, sound or touch, without anyone meaning to pass it.
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What is sensory leakage?
An experiment on telepathy or clairvoyance only means something if the normal routes are closed. Sensory leakage is the name for any route left open. A card can show through its back in a slanting light. An experimenter who knows the answer can shift, pause or breathe differently at the right guess. A picture handled by a sender carries creases and smudges that the other three in the set do not.
None of this requires cheating. People pick up such cues without knowing that they do, and the people giving them do not know either. The remedies are well understood: nobody in contact with the subject may know the target, targets are chosen by a random process, duplicate sets are used for judging, and sender and receiver are kept in separate, sound-proofed rooms.
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What sets Sensory Leakage apart
Leakage differs from fraud in needing no intention and from chance in having a direction. It pushes scores one way, toward the target, and it does so quietly enough that honest experimenters report the result as genuine. It is also specific to the design: each kind of test has its own leak, the card back, the handled photograph, the voice of the tester, so each new method has had to be checked afresh. Automation, in which a computer picks and shows the target, was the field's main answer.
- Routes: sight, sound and touch; marks on targets; the manner of a tester
- Classic case: Clever Hans, explained by Oskar Pfungst in 1907
- Early finding: Lehmann and Hansen, 1895: unconscious whispering
- Card tests: some printed packs of the 1930s could be read from the back
- Ganzfeld cue: a target handled by the sender shown to the receiver for judging
- Agreed standards: the joint paper of Hyman and Honorton, 1986
Often mistaken for something else: The file-drawer problem concerns which studies get published; sensory leakage concerns what went on inside a single study.
The story behind Sensory Leakage
In 1895 the Danish researchers Lehmann and Hansen showed that faint unconscious whispering could account for early results in thought transference. In 1907 Oskar Pfungst showed that the horse Clever Hans, who seemed to do sums, was reading the posture of his questioners. Critics of the 1930s found that some printed test cards could be read from the back. In 1986 Ray Hyman and Charles Honorton jointly published standards for ganzfeld work meant to shut every such channel.
Why Sensory Leakage matters
Sensory Leakage is the first ordinary explanation any positive result must exclude, and the history of the field is largely a history of closing it.
How to read Sensory Leakage
Critics apply it to any experiment where a person who knew the target could be seen or heard; researchers design protocols to exclude it.
Sensory Leakage in practice: an example
In a card test at home, a guesser who can see the sender's face scores higher than one seated behind a screen, with no power involved.
Where readings of Sensory Leakage go wrong
Showing that leakage was possible in a study does not show that it happened, only that the result cannot be relied on.
Sources and editorial method
This entry summarizes the tradition in the Almanac's own words; where no source is listed, it is an editorial summary rather than a primary text, and symbolic readings are named as the tradition's, not as fact.
- Source
- The Great Almanac Dictionary
- Category
- Consciousness & Spiritual Psychology
- Aliases
- sensory leakage meaning, sensory cues esp, sensory leakage parapsychology, sensory leakage ganzfeld, unconscious cues
- Last updated
- 2026-09-26
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More in Consciousness & Spiritual Psychology
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Common questions
What is sensory leakage?
It is the unintended passing of information to a test subject by normal means, such as a glimpse, a sound, a mark on a card or the manner of someone who knows the answer. It can produce scores above chance with no unusual faculty.
How do experimenters prevent sensory leakage?
By keeping everyone who meets the subject ignorant of the target, separating sender and receiver in shielded rooms, selecting targets at random and using duplicate copies for the judging so that handled items carry no clues.
What does Clever Hans have to do with ESP research?
The horse seemed to answer questions by tapping a hoof, and in 1907 was shown to be responding to tiny involuntary movements of the people watching. The case proved how readily unnoticed cues can pass, and it is why testers are kept blind.
