Is There a Sixth Sense?

Some experts claim that hunches might actually foretell the future. Others aren't so sure.

By Dean Radin, Colleen Rae, Ray Hyman, published on July 1, 2000 - last reviewed on June 9, 2016

Ever have a hunch, an instinct or an intuition? Research psychologist Dean Radin, Ph.D., claims that hunches might actually foretell the future. The University of Oregon's Ray Hyman, Ph.D., however, isn't so sure.

Alex, a university colleague, was cleaning his double-action, six-shot revolver in preparation for a hunting trip later in the month. In this pistol, when the trigger is pulled the hammer is cocked, the cylinder revolves, and the hammer falls on the next chamber, all in one smooth motion. For safety's sake, Alex normally kept five bullets in the revolver, with the hammer resting on the sixth, empty chamber.

Before cleaning the gun, he removed the five bullets and set them aside. When finished cleaning, he began to put the bullets back in the cylinder. When he arrived at the fifth and final bullet, he suddenly got a distinct sense of dread. It had something to do with that bullet.

Alex was bothered about the odd feeling because nothing like it had ever happened to him before. He decided to trust his gut, so he put the bullet aside and positioned the pistol's hammer as usual over the sixth chamber. The chamber next to it, which normally held the fifth bullet, was now also empty.

Two weeks later, Alex was at a hunting lodge with his fiancee and her parents. That evening, unexpectedly, a violent argument broke out between the parents. Alex tried to calm them down, but the father, in an insane rage, grabbed Alex's gun, which had been in a drawer, and pointed it at his wife.

Alex tried to intervene by jumping between the gun and the woman, but he was too late—the trigger was already being pulled. For a horrifying split second, Alex knew that he was about to get shot at point-blank range. But instead of a sudden, gruesome death, the pistol went "click." The cylinder had revolved to an empty chamber—the very chamber that would have contained the fifth bullet if Alex had not set it aside two weeks earlier.

Had Alex actually predicted the future, or was this just an extraordinary coincidence? There are several possible explanations for why such "intuitive hunches" sometimes play out. One is that on a subconscious level, we are always thinking and coming to conclusions, but that these register only as hunches to our conscious mind. Another is that we pick up telling cues from body language, subliminal sounds or peripheral vision without being consciously aware of doing so. A third is that for each amazing coincidence we remember, we forget all the times we had a hunch and it didn't pan out. A fourth possibility is that we modify our memories for our own convenience, creating a connection where it may not have existed. And so on. These sorts of prosaic explanations probably account for many intuitive hunches. But they don't explain them all.

As in the case of Alex's intuition, a series of carefully documented case studies raises the possibility that some intuitions are due to a genuine sixth sense. But to confirm that those stories are what they appear to be, we must turn to controlled laboratory tests.

In a pilot study and in three follow-up experiments, I have observed that many people respond unconsciously to something bad—even before it happens. Take the prototypical case of a well-known editor of a popular magazine. When she asks the question, "Is there a sixth sense?" I don't answer directly. I ask if she'd like to participate in an experiment that uses pictures randomly selected by computer, and she agrees.

I have her sit before a blank computer screen. All I've told her is that she's about to see a series of digitized photographs. Some will be calm, like a placid lake, and others will be emotional, like a big spider. On two fingers of her left hand, I attach electrodes that measure tiny changes in her skin resistance. On a third finger I place an electrode that monitors blood flow. I explain that all she has to do is press the button on the mouse when she's ready to begin, and then look at the pictures.

I leave the room, she relaxes, and then she presses the button. For five seconds, the screen remains blank, and then the computer randomly selects one picture out of a large pool of photos—some calming and some provocative. The picture is displayed for three seconds, and then the screen goes blank for eight seconds. Finally, a message appears announcing that she can start the next trial whenever she's ready.

She repeats this sequence 40 times. At the end of the experiment, I analyze the data recorded by the electrodes and prepare two summary graphs. Each graph shows average changes in her skin resistance and blood flow before, during and after she saw either calm or emotional pictures. What she immediately notices is that after she viewed the emotional pictures, both her skin resistance and fingertip blood flow dramatically changed. And after she viewed calm pictures, her physiology hardly changed at all.

"So I responded emotionally when I saw something emotional, and I remained calm when I saw something calm," she says. "How does that demonstrate a sixth sense?"

I direct her attention to the segment of the graph showing her responses before the computer selected the pictures. "This bump shows that your body responded to emotional pictures before the computer selected them. And this flat line," I say, pointing to the other line, "shows that your body did not respond before calm pictures were shown. You see? Your body was responding to your future emotion before the computer randomly selected an emotional or calm picture."

As this sinks in, I add, "We can now demonstrate in the laboratory what at some level we've known all along: Many people literally get a gut feeling before something bad happens. Our viscera warn us of danger even if our conscious mind doesn't always get the message."

Our editor's body showed signs of what I call presentiment, an unconscious form of "psi" perception. Psi is a neutral term for psychic experiences, and though it sounds like fodder for an episode of the X-Files, scientists around the world have studied the subject in the laboratory for over a century. The scientific evidence is now stronger than ever for commonly reported experiences such as telepathy (mind-to-mind communication), clairvoyance (information received from a distant place) and precognition (information received from a distant time). Studies suggest that we have ways of gaining information that bypass the ordinary senses. The sixth sense and similar terms, like second sight and extrasensory perception (ESP), refer to perceptual experiences that transcend the usual boundaries of space and time.

In trying to take these findings further, I realized that we have to dig deeper than what's detectable at the conscious level. While ESP and psi generally refer to conscious psychic experiences, I've always thought that asking people to consciously report subtle psi impressions was a shot in the dark. What would happen if we bypassed the psychological defense mechanisms that filter our perceptions and censor our conscious awareness? Would we find psi experiences that people weren't aware of?

A handful of colleagues have paved the way for this type of investigation. In the mid-1960s, psychologist Charles Tart, Ph.D., of the University of California at Davis, measured skin conductance, blood volume, heart rate, and verbal reports between two people; called a sender-receiver pair. He, as the sender, received random electrical shocks to see if remote receivers could detect those events. Tart found that while they weren't consciously aware of anything out of the ordinary, the distant receivers' physiology registered significant reactions to the shocks he experienced.

In other, independent experiments, engineer Douglas Dean at the Newark College of Engineering; psychologist Jean Barry, Ph.D., in France; and psychologist Erlendur Haraldsson, Ph.D., at the University of Utrecht, all observed significant changes in receivers' finger blood volume when a sender, located thousands of miles away, directed emotional thoughts toward them. The journal Science also published a study by two physiologists who reported finding significant correlations in brain waves between isolated identical twins. These sorts of studies came to be known as Distant Mental Intention on Living Systems (DMILS).

The idea for studying intuitive hunches came to me in the early 1990s, while I was a research fellow in the psychology department at the University of Edinburgh in Scotland. I was investigating the "feeling of being stared at." In the laboratory, I separated two people, placing them in rooms that were 100 feet away from each another. Then I monitored person number 1's electrodermal activity while person number 2 stared at person number 1 over a one-way closed-circuit video system. Although the stared-at person could have no conscious idea when the "starer" was doing the looking, since the two were in different rooms and the staring occurred at random times, I did observe small changes in the skin resistance of the person being stared at over closed-circuit television.

In thinking about this result, I realized that (for relativistic reasons) this sort of "nonlocal" connection across space implied a complementary connection across time. If we were seeing a genuine space-separated effect between people, then the same thing ought to work as a time-separated effect within one person. I called this proposed effect "presentiment" because the term suggests a response to a future emotional event.

I soon discovered that even the staunchest skeptics, those ready to swear on a stack of scientific journals that psi was impossible, were somewhat less critical of intuitive hunches. That's because most people have had at least one.

I myself hardly believed the results of the studies I conducted on the magazine editor and others. But I couldn't find any mistakes in the study design or analysis of the results. Some months later, Dick Bierman, Ph.D., a professor at the University of Amsterdam, learned of my studies and couldn't believe them either. So he repeated the experiment in his lab and found the same results. Since then, two students of psychologist Robert Morris, Ph.D., at the University of Edinburgh, have also repeated the study, and again found similar results. More replication attempts are now under way in several other laboratories.

Do our experiments prove without question that the sixth sense exists? Not yet. What we have are three independent labs reporting similar effects based on data from more than 200 participants. The proof of the pudding will rest upon many more labs getting the same results. Still, our studies, combined with the outcomes of many other types of tests by dozens of investigators on precognition and other classes of psi phenomena, have caused even highly skeptical scientists to ponder what was previously unthinkable—the possibility of a genuine sixth sense.

In the mid-1990s, for example, no less an arch-skeptic than the late astronomer Carl Sagan rendered his lifelong opinion that all psi effects were impossible. But in one of his last books, The Demon-Haunted World: Science as a Candle in the Dark, he wrote, "At the time of writing there are three claims in the ESP field which, in my opinion, deserve serious study: (1) that by thought alone humans can (barely) affect random number generators in computers; (2) that people under mild sensory deprivation can receive thoughts or images "projected" at them; and (3) that young children sometimes report the details of a previous life, which upon checking turned out to be accurate and which they could not have known about in any other way than reincarnation."

If scientists eventually agree that a sixth sense exists, how might this change society? On one hand, it may change nothing; we may learn that genuine psi abilities are rare and only weakly predictive, and thus inconsequential for most practical purposes.

On the other hand, it's possible that the study of the sixth sense will revolutionize our understanding of causality and have radically new applications. For example, in an article co-titled 'Exploring an Ourtageous Hypothesis,' psychologist William Braud, Ph.D., professor and research director at the Institute of Transpersonal Psychology and co-director of the Institute's William James Center for Consciousness Studies, discusses the concept of "retroactive intentional influence" as applied to healing. He poses the idea that in cases where serious illnesses disappear virtually overnight, perhaps a healer went back in time to jumpstart the healing process.

Braud is well aware of the mind-bending nature of this hypothesis, but it is not purely fantastical. In his article, he reviews several hundred experiments examining a wide range of retrocausal phenomena, from mental influence of random numbers generated by electronic circuits, to guessing picture targets selected in the future, to studies examining the "feeling of being stared at," to presentiment experiments. He concludes that this sizable but not well-known body of carefully controlled research indicates that some form of retroactive intentional influence is indeed possible, and may have important consequences for healing.

A less radical application might be for early warning systems. Imagine that on a future aircraft all the members of the flight crew are connected to an onboard computer system. The system is designed to continuously monitor heart rate, electrical activity in the skin, and blood flow. Before the crew comes aboard, each person is calibrated to see how he or she responds before, during and after different kinds of emotional and calm events. Each person's idiosyncratic responses are used to create a person-unique emotional "response template," which is fed into the computer.

While the plane is in the air, the computer monitors each crew member's body to assess their emotional level. If the computer detects that all crew members are about to have an emotional response (and the aircraft is otherwise operating normally), then the computer could alert the pilot. Sometimes even a few seconds of advance warning in an aircraft can save the lives of everyone on board.

Very likely, some intuitive hunches do indicate the presence of a sixth sense. But for whom? Probably everyone, to a degree. But just as some people have poor vision, it is also quite likely that some people are effectively "psi-blind." I suspect that in the future, with a little assistance from specialized technologies, the same way a hearing aid can improve poor hearing, it may become possible to boost our weak sixth sense.

Where's the Science in Psi?

Dean Radin asks, "Do our experiments prove without question that the sixth sense exists?" He then answers, "Not yet," correctly recognizing that we need further successful experiments, by independent investigators, to prove that such a sixth sense is real.

But even that's not so simple. The independent investigators must do more than duplicate Radin's findings. They must do so using different apparatus, measurements and randomizing procedures than he did to avoid replicating any errors he may have made inadvertently, otherwise they're just perpetuating faulty findings.

I can already spot some potential errors in his methods. For example, Radin's claim that people in his presentiment experiments unconsciously anticipated emotional pictures—based on his observation of changes in their skin resistance—violates some basic principles of cause and effect in science. That's because the case for presentiment rests on comparing changes in physiological states, and different methods of calculating such changes can yield wildly different results.

For example, many years ago, a student was doing research to show that blinded rats are better than sighted rats at transferring their learning to a new task. The trouble was, a previous researcher had found just the opposite effect. The difference between the two studies? How they measured change. The earlier researcher had calculated the simple difference between the number of errors the rats made on the first task and the number of errors they made on the second task; the student, meanwhile, had measured the changes in terms of percentages. This seemingly innocuous difference led to completely opposite findings! When we used the same measuring technique on both studies, they yielded uniform results.

In addition to the potential pitfalls of choosing a measuring method, researchers must also account for the great degree of variability of physiological changes, which Radin does not do convincingly. Skin resistance, like other physiological measures, varies greatly from person to person and over short and long periods. It also reacts to many aspects of the test subjects' internal and external environment, which is why investigators use a number of adjustments to remove unwanted variation so they can focus only on the changes in which they are interested.

While to his credit, Radin does try to reduce some unwanted variability, his efforts seem to be indirect and arbitrary at best, especially when the process can be very tricky. Radin measured the change in physiological states by subtracting the very first sample of skin resistance on each trial from all the remaining samples of skin resistance for that trial. The evidence for presentiment, he says, is the fact that the averages of the change in skin resistance are larger before viewing emotional pictures than before calm pictures. That seems to make sense. But the first samples of skin readings taken in the trial set the baseline against which the results of all future trials will be compared and computed. So if, for some reason, the first samples of the trials involving emotional targets happen to have a somewhat lower value of skin resistance than the first samples of the calm trials, this alone would yield, perhaps falsely, a bigger "change score" for the emotional trials.

To see this problem in action, assume that the average raw score level for both calm and emotional trials is 20. If the baseline for the calm trials is 15, then the change score for the calm trials would be 20-15=5. If the baseline for the emotional trials is 10, then the change score for the emotional trials would he 20-10=10. Thus, the scoring procedure produces a bigger change in the emotional trials, all because of the differences in baselines. As you can see, the simple choice of method can greatly influence the findings. The devil, as they say, is in the details.

So how do we know which measure to trust when each gives a different outcome? The solution is clear only when we have a detailed theory of the underlying process being studied. But that's a key problem here: There is a general lack of a positive theory of ESP or psi. What kind of a process is it? How does it behave? Indeed, as many parapsychologists recognize, ESP is, at present, defined negatively, in terms of what it is not; the experimenter claims she has found psi when she has eliminated all normal scientific explanations for the outcome. Given this hazy state of affairs, there is no principled way to state what the correct measurement procedure should he. This would not be too serious if different methods produced the same outcome. But we do not know if this is the case in Radin's experiments.

If I am investigating changes in the firings of nerve impulses in the optic nerve, for example, we have both extensive theory and data to inform us of the appropriate measures to use: We know the underlying distribution of such firings and we know how to appropriately transform them so that the measures of change make sense in terms of what we know about nerves and nerve impulses, in the case of the presentiment hypothesis, however, we do not have a detailed theory and sufficient data to know what sorts of transformations and measures of change make sense. So before we can believe that the physiological changes show that the subject is anticipating the emotional picture, we need to show, at the least, that different ways of measuring the physiological changes will yield the same outcome. We also would need to collect the physiological measures under more varied circumstances and over longer time periods.

The history of attempts to investigate scientifically psychical phenomena goes back 150 years, and is replete with examples of psychical researchers claiming they finally proved the existence of the paranormal. In each instance, subsequent generations of parapsychologists have had to discard as badly flawed what had seemed to the previous generation to be irrefutable proof of psi, or psychic phenomena.

A case in point is the study cited by Radin of the "significant correlations in brain waves between isolated identical twins." This study was reported in the journal Science in 1965 by Duane and Behrendt. These investigators took advantage of the fact that alpha brain waves can be induced by simply closing one's eyes. The researchers put two members of a pair of twins in separate rooms and connected them to electrodes to measure their brain waves. They instructed one of the twins to shut her eyes at predetermined times. This produced the expected alpha rhythms in her brain waves, and supposedly caused the other twin's brain waves to show alpha rhythms at the same time. If this is indeed what had happened, it would be evidence for ESP. But there were many methodological problems. First, the isolation of the twins was not very convincing since they were in adjacent rooms. Second, the evidence for the correlation of the brain waves was based solely on subjective, visual inspection of the brain wave recordings. As psychologists know, people are very poor at determining correlations subjectively, which is why experimenters trust only correlations tabulated by computers.

Duane and Behrendt later admitted, among other things, that because the twins were not in shielded rooms, they could conceivably have sent coded signals to one another. "In retrospect, the biggest defect in our experimental procedure was that we did not rule out completely conventional forms of communication between the twins, and we did not perform a statistical analysis to eliminate spontaneous alpha rhythms." While they continued to seek the "hard, quantitative data" they said would prove or refute the hypothesis, neither these authors or anyone else has succeeded, during the intervening 45 years, in replicating these results under scientific conditions.

In his book The Conscious Universe, Dean Radin remains optimistic that, correctly interpreted, the experimental outcomes of parapsychological experiment conclusively demonstrate the existence of psi or ESP.

But if the century and a half of psychical research has taught us anything, then the next generation will likely not be able to replicate Radin's presentiment results and will begin to search elsewhere for their elusive quarry. On the other hand, if history ceases to repeat itself, future parapsychologists may very well find ways to help us develop our intuitive powers; it remains to be seen whether Radin's research will pave the way.