Extrasensory perception or ESP as it is commonly known is a term coined by Dr. J. B. Rhine of the Parapsychology Laboratory at Duke University. ESP includes telepathy, clairvoyance and pregconition (sensing future events psychically in dreams, visions or hunches). Extrasensory perception meaning the psychic awareness without communicating through the senses of sight, hearing or other ordinary sensory channels. The difference between clairvoyance and precognition is the time element involved. Clairvoyance and its counterparts, clairaudience and clairsentience are the ability to sense at the same time the event is happening. Precognition is the ability to sense before the event takes place.

While it is thought that most ESP experiences are spontaneous, science has also shown us that people can now be trained to zoom in on their ESP skills by increasing conscious awareness either under controlled conditions such as hypnotherapy or related techniques or by a gradual self learning process. ESP generally occurs in a relaxed or dissociated state, that of being out of touch with ones environment. One may be daydreaming, sleeping, in a trance and what Rosalind Heywood refers to as "a more or less inactive brain". Sometimes psychic experiences will come when a person is in a expanded state of consciousness or hyperawareness.

Instances of telepathic exchange are sometimes motivated by an emotionally troubled or aroused feeling that is communicated to the receiver. It is in these cases that a person would communicate fear, anger, or sadness over an event, usually that of a highly stressful situation. Not all cases are that dramatic and the sender's feelings will be on a more mild tone and communicated because of the sympathetic bond between sender and receiver. These bonds are most commonly found between members of the same family, lovers, friends and perhaps those working closely together. This even flows over to laboratory experiments as Thelma Moss, a parapsychologist at the University of California at Los Angeles experienced between her experiment subjects. She believes that for a successful experiment, subject and sender should be intimately related, the receiver in a relaxed state and the sender in a highly charged emotional state which acts to increase the electrical activity in the body and believed to speed up psychic communication.

The telepathic signal is not always sent and received at the same time. There is often a period of latency between sending and receiving. Scientists believe that the receiver in these cases holds the message in his or her subconscious until there is a need to let it filter up to the conscious level. While the sender is thought to start the telepathic exchange in most cases, in recent years a new theory has arisen that suggests that the generating force in spontaneous cases sometimes comes from the receiver. Rosalind Heywood relates in her book, The Infinite Hive, that "A person who is emotionally drawn to another might, at all times, be 'scanning' for him or her subconsciously." In these cases, it is the receiver that seems to be tuned into the sender like a radio and listening at a subliminal level rather then the sender initiating contact. Another theory abroad is that when there is a close relationship between sender and receiver that neither actively sends nor receives the telepathic signal but that they share a psychic field in which it arises.

In "intuition" or "impression" cases there is less extra-sensory imagry and more of a feeling involved. For example, the sender may be ill or in danger some distance away from the receiver. Instead of receiving a thought or having a mental vision, the receiver may react with a change of mood or a fit of depression without consciously knowing the cause or an urgent need to stop what he or she is doing and find the person, usually a close friend or relative that is in trouble. In many cases of telepathic impressions, neither sender nor receiver may be aware that a message was sent or received.

ESP can come in the form of voices or sounds, referred to as "clairaudience" and may seem to originate from the outside or may be heard in the mental ear but their actual source is often outside of hearing range. ESP can also come in the form of pain or even a physical blow. In one case, famous psychiatrist Carl Jung relates the story of waking up one night with the sensation of a blow to the back of his head. The next day he learned that one of his patients had shot himself in the head. ESP can be experienced in every kind of physical sensation that exists. The sense of taste has even been experimented with under hypnosis where the tester placed different foods in his mouth while his hypnotized subject in the next room accurately identified every single substance.

When the Rhines set up their laboratory at Duke University in 1930, they used the "quantitive" approach to measure the actual amount of ESP that shows using statistical methods. The clairvoyance experiments used a system of 5 symbols where the subject would try to accurately guess out of a run of 25 cards. The cards used for the clairvoyance experiments are called Zenner cards or ESP cards with the five symbols- circle, star, rectangle, cross, and three wavy vertical lines. Statistically, a guess of 1 out of 5 or 5 out of 25 over many runs through the deck would indicate that the guesses were chance and not ESP. A score of above 5 out of 25 over hundreds of runs would be statistical proof of clairvoyance. There is more subjectivity in scoring this way because other experiments having a subject draw what was in the sender's mind, the sketch might be similar in form or details but hard to put a hard score on depending on different interpretations acrosst the board. The difference between testing for a telepathy and a clairvoyance experiment is that for telepathy, the sender tries to send his thoughts to the subject mind. In clairvoyance tests, the subject may be able to handle the object but he does not know what it is. If a playing card or picture is used, it is laid face down, put in an envelope or otherwise hidden from his view.

When Rhine started his laboratory, his first main objective was merely to find out if anyone had psychic ability. He used mostly students from the university but also tested some of the prominent psychics at the time like Eileen Garrett. Some students scored as high as 8 and 9 correct cards per 25 cards over several hundred trial runs. The most outstanding student was Hubert Pearce, a divinity student, who not only scored much higher then chance but once made 25 out of 25 guesses in a row. The statistical odds against this event are an astounding 298,023,223,876,953,125 to 1! The highest score ever made in the ESP card test was made by a female student at Hunter College in New York in 1937. Her average was more then 18 hits per 25 guesses in 74 runs through the deck. Thats 1,349 correct answers to 1,859 tries. Chance would dictate there to have been only 370 correct guesses.

Dr. Rhine found that generally at the beginning of a series of tests, the novelty or gamelike quality of the situation resulted in high scores but that both interest of the subject and the score declined somewhere in the middle of the testing. The score would generally rise again in the later stages. He coined this as the "decline effect". Dr. Gertrude Schmeidler of City College of New York made the observation that subjects who were friendly and outgoing and believe in ESP and their ability would produce better scores in tests then the introverted, skeptical subjects. She called the extroverted subjects "sheep" and the introverted skeptics "goats". Surprisingly, many of the "goats" would prove psi ability by scoring consistently below chance. To her, this indicated that they could as easily hit the target if they so chose, consciously or unconsciously, to be "psi-missers" by avoiding the target.

The main objection of scientists in ESP tests is the failure to achieve repeatability or doing the same experiment over and over again under identical conditions and getting identical results. This remains a problem because the mind cannot be captured and pigeon-holed the way physical and chemical substances are isolated in a laboratory setting. There are many factors that seem to operate in an ESP experiment and they may change from one experiment to the next even though the laboratory conditions are ostensibly the same. The personality and attitude of the experimenter, the physical and emotional condition of the sender and receiver, the unsettling presence of skeptical observers, even the weather may subtly alter the circumstances of the experiment.

Although women seem to show more interest in psychic phenomena, there is no conclusive evidence that shows that women have more psi ability then men. It is interesting to note, however, that when the sender and receiver of a test are of the opposite sex, it often stimulates more interest and higher scores. It is thought that men are better senders and women are better receivers although parapsychologists are not in total agreement on this point. According to J.B. Rhine, age is not a limiting factor either. Children as a group seem to make the highest scores, possibly because they do not have the self-doubts and inhibitions of their adult counterparts. Most parapsychologists including Rhine and Murphy feel that ones general attitude towards the tests is more significant then age. It has also theorized that intelligence may inhibit ESP if the subject analyzes what he is doing. Members of MENSA showed strong interest in ESP tests but did not score above chance as a group. There is however, good evidence that psi runs in families. Many of Rhine's best subjects said that members of their families were psychic in some means. Most mediums claim that the faculty is inherited. Research has also shown amazing abilities between twins.

After years of testing subjects and evaluating spontaneous cases, most parapsychologists now believe that everyone has the psychic sense to some degree and that psi is universal and can in most cases be learned.