Brain neuroimaging experiments find 'evidence against existence of psi' … or do they?

Can imaging of the brain help resolve the debate over whether psi exists or not? Two researchers at Harvard University think it can, and in fact they have now published neuroimaging results that they say "are the strongest evidence yet obtained against the existence of paranormal mental phenomena."

The researchers note that despite widespread public belief in paranormal mental phenomena such as telepathy or mind-reading, also known as psi, "there is not compelling evidence that psi exists."

Among academic scientists, psychologists especially tend to be skeptical of reports of psi, particularly the anecdotal kind that impress people unaware of all the psychological biases that allow them to so easily misinterpret evidence: the clustering illusion, availability error, confirmation bias, illusion of control, and many others.

But if psi processes do exist, they are a mental activity, and there should be some way to detect that activity in the brain by modern neuroimaging techniques. Samuel T. Moulton and Stephen M. Kosslyn of the Harvard Psychology Department feel strongly that with sophisticated neuroimaging techniques, psychology is in a position to advance the psi debate, which in the past "has produced more heat than light." They set up experiments using functional magnetic imaging (fMRI) of the brain to try to document the existence of psi.

They wanted to see if the brain might respond selectively to purported psi stimuli. By "psi stimuli" they mean stimuli presented not through the usual senses but telepathically (mind to mind), clairvoyantly (world to mind), and precognitively (future to present). They designed the experiment to produce positive results if telepathy, clairvoyance, or precognition exist. They made minimal assumptions about psi and think they have offered the broadest possible test of the psi hypothesis.

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The researchers used sixteen pairs of paid volunteers, thirty-two people total. Some were couples, some emotionally close roommates or friends. There was one mother-son pair, one pair of sisters, and two identical twin pairs. Fourteen were men, eighteen were women.

Each pair designated one of its members as "sender" and one as "receiver." The test stimuli consisted of 240 pairs of unique photographs covering a range of content, from emotionally negative pictures (a snake, a dead body, a violent scene) to neutral and positive pictures (a tissue box, a wedding, an erotic couple). They randomly assigned each picture to a stimulus category (psi, non-psi) and ensured that across participants each picture was assigned to each category an equal number of times.

The receiver's head was placed in a high-speed magnetic resonance scanner, and a series of forty-eight trials for each volunteer pair began. The sender of each pair, in a separate room, was signaled to sequentially view the images for ten to twenty-two seconds and then to try to "influence the receiver" with the psi stimulus ("sending" one image). They were asked to adopt a "playful" attitude, maintain an active interest in the stimuli, and use whatever "sending" tactics they deemed appropriate. (In this they were following the advice of parapsychology researchers who believe certain attitudes are conducive to psi.)

The receiver was presented a pair of photos (projected onto a mirror attached to a head coil) and then told to press a button selecting which one he or she felt was the psi stimulus. The receiver then viewed the psi stimulus a second time to account for the possibility of precognition.

One set of results showed the participants performed almost exactly as they would by chance on the guessing task. Out of 3,687 recorded responses, the receivers correctly guessed the psi stimulus 1,842 times (50.0 percent).

But the key results were the comparison of brain activation for psi stimuli versus non-psi stimuli. The researchers looked for anatomical locations across the brain that responded differently to these stimuli for the entire group and for each individual recipient. Analysis of the group data revealed "no evidence whatsoever of psi." Psi and non-psi stimuli evoked widespread but indistinguishable neuronal responses.

"The results support the null hypothesis that psi does not exist," report Moulton and Kosslyn in the Journal of Cognitive Neuroscience (20:1, 2008). "The brains of our participants--as a group and individually--reacted to psi and non-psi stimuli in a statistically indistinguishable manner." The results cannot be explained by a lack of statistical power, they say. "Even if the psi effect were very transient, as are many mental events, it should have left a footprint that could be detected by fMRI."

The researchers say they went out of their way to incorporate variables (biological relatedness of participants, evocative stimuli) widely considered by parapsychologists to help facilitate psi.