Extrasensory perception (ESP), also called a sixth sense or cryptaesthesia, is a claimed ability to receive information without using the usual physical senses, such as sight or hearing. Instead, the information is said to be sensed through the mind. The term ESP was introduced by J. B. Rhine, a botanist from Duke University, to describe psychic abilities like telepathy (reading minds), psychometry (gaining information from objects), and clairvoyance (seeing things not visible to others). These abilities may also involve perceiving events before they happen (precognition) or after they occur (retrocognition).
Second sight is a type of extrasensory perception in which a person claims to see visions about future events (precognition) or events happening in distant places (remote viewing). However, there is no strong scientific evidence that second sight exists. Reports of second sight are based only on personal stories and are not supported by research. Both second sight and ESP are considered pseudosciences, meaning they are not recognized as valid scientific fields.
History
In the 1930s, at Duke University in North Carolina, J. B. Rhine and his wife, Louisa E. Rhine, studied extrasensory perception (ESP). Louisa collected stories about people who claimed to have ESP experiences without being tested. J. B. Rhine worked in the laboratory, where he defined terms like ESP and psi (parapsychology) and created experiments to test these ideas. A simple set of black and white cards, first called Zener cards and now called ESP cards, was used in these tests. Each card has one of five symbols: a circle, square, wavy lines, cross, or star. A pack of 25 cards contains five of each symbol.
In one experiment, a "sender" looked at the cards while a "receiver" guessed the symbols. To test clairvoyance, the cards were hidden from both people during guessing. To test precognition, the card order was decided after the guesses were made. Later, Rhine used dice to study psychokinesis, which is the idea of influencing objects with the mind.
Rhine's experiments faced criticism from scientists and others who doubted the evidence for ESP. Many psychology departments tried to repeat his experiments but failed. In 1936, W. S. Cox from Princeton University tested 132 people in an ESP card experiment with 25,064 trials. Cox concluded there was no evidence of ESP in the people tested. He believed the differences between his results and Rhine's were due to problems in how the experiments were conducted or differences in the people tested. Other psychology departments also failed to copy Rhine's findings.
In 1938, psychologist Joseph Jastrow said much of the evidence for ESP collected by Rhine and others was based on stories, biased observations, or errors. Later, it was found that some of Rhine's results could be explained by accidental clues or cheating, such as subjects seeing the symbols from the back of the cards or noticing small hints from the experimenter.
In the 1960s, parapsychologists began studying the mental processes behind ESP, the personal experiences of people who claim to have ESP, and how ESP might relate to psychology. This led to new experiments beyond Rhine's methods, such as tests involving dreams and the ganzfeld experiment, which limits sensory input to study ESP.
The term "second sight" may have come from the idea that normal vision is the first ability, while seeing things beyond normal limits is a second ability, limited to certain people. In Gaelic, "an dà shealladh" means "the two sights" and refers to the ability to see the future or distant events. While this term is widely recognized by non-Gaelic speakers, it technically means "two sights" rather than "second sight."
Skepticism
Parapsychology is the study of unusual mental abilities, such as extrasensory perception (ESP). Over 100 years of research has not produced strong evidence to support the existence of these abilities, and many scientists criticize the field for continuing to investigate without clear proof. The scientific community does not accept ESP as real because there is no solid evidence, no explanation for how it might work, and no experiments have shown consistent results. Scientists consider ESP to be pseudoscience, meaning it is not based on reliable scientific methods.
Most scientists do not believe extrasensory perception is a real scientific phenomenon. Skeptics argue that there is no clear explanation for how ESP could work, and past studies have shown problems with how experiments were designed. Many experiments testing ESP have flaws in their methods, which make the results unreliable. These flaws are not limited to one type of experiment and have weakened the credibility of many studies. For example, the Zener cards experiment and the Ganzfeld experiment both had similar issues.
One problem is the "stacking effect," which happens when feedback is given during trials using a fixed sequence of targets, like a deck of cards. This creates a situation where responses are not independent, making it easier for participants to guess correctly without using ESP, such as by counting cards. Another issue is "sensory leakage," where participants accidentally receive clues through their senses, like seeing a reflection of a card in a researcher’s glasses. This allows them to guess correctly without ESP. Poor randomization of target items, such as not shuffling cards properly or using marked cards, also makes it easier to predict results. A review of many studies found that even after fixing these problems, no strong evidence for ESP remained. Some studies seemed to show ESP, but this was likely due to the flaws in their methods.
In the early 1900s, Joaquin María Argamasilla, called the "Spaniard with X-ray Eyes," claimed he could read handwriting or numbers on dice inside closed metal boxes. He tricked scientists like Gustav Geley and Charles Richet into believing he had psychic powers. However, in 1924, magician Harry Houdini exposed him as a fraud. Argamasilla secretly peeked through his blindfold and lifted the edge of the box to look inside without being noticed.
Science writer Martin Gardner noted that many investigations into people who claim to have "second sight" have failed to recognize how psychics use tricks with blindfolds to deceive others. He described how individuals like Rosa Kuleshova, Lina Anderson, and Nina Kulagina used techniques to peek through their blindfolds and trick investigators into thinking they had supernatural abilities.