A respected peer-reviewed journal in psychology, The Journal of Personality and Social Psychology, is about to publish a paper that presents scientific evidence for precognition. The paper, by Daryl Bem of Cornell University, is called “Feeling the future: Experimental evidence for anomalous retroactive influences on cognition and affect,” and you can download a preprint on his webpage. I’ve scanned the paper only briefly, and am posting about it in hopes that some of you will read it carefully and provide analyses, either here or elsewhere.

The paper purports to show that a choice that you make in a computer test can be influenced by stimuli you receive after you’ve already made the choice. This implies you have some way, consciously or unconsciously, of detecting things that haven’t yet happened. In an article in Psychology Today, “Have scientists finally discovered evidence for psychic phenomena?“, psychologist Melissa Burkley at Oklahoma State University summarizes two of Bem’s studies:

However, Bem’s studies are unique in that they represent standard scientific methods and rely on well-established principles in psychology. Essentially, he took effects that are considered valid and reliable in psychology – studying improves memory, priming facilitates response times – and simply reversed their chronological order. For example, we all know that rehearsing a set of words makes them easier to recall in the future, but what if the rehearsal occurs after the recall? In one of the studies, college students were given a list of words and after reading the list, were given a surprise recall test to see how many words they remembered. Next, a computer randomly selected some of the words on the list as practice words and the participants were asked to retype them several times. The results of the study showed that the students were better at recalling the words on the surprise recall test that they were later given, at random, to practice. According to Bem, practicing the words after the test somehow allowed the participants to “reach back in time to facilitate recall.” In another study, Bem examined whether the well-known priming effect could also be reversed. In a typical priming study, people are shown a photo and they have to quickly indicate if the photo represents a negative or positive image. If the photo is of a cuddly kitten, you press the “positive” button and if the photo is of maggots on rotting meat, you press the “negative” button. A wealth of research has examined how subliminal priming can speed up your ability to categorize these photos. Subliminal priming occurs when a word is flashed on the computer screen so quickly that your conscious brain doesn’t recognize what you saw, but your nonconscious brain does. So you just see a flash, and if I asked you to tell me what you saw, you wouldn’t be able to. But deep down, your nonconscious brain saw the word and processed it. In priming studies, we consistently find that people who are primed with a word consistent with the valence of the photo will categorize it quicker. So if I quickly flash the word “happy” before the kitten picture, you will click the “positive” button even quicker, but if I instead flash the word “ugly” before it, you will take longer to respond. This is because priming you with the word “happy” gets your mind ready to see happy things. In Bem’s retroactive priming study, he simply reversed the time sequence on this effect by flashing the primed word after the person categorized the photo. So I show you the kitten picture, you pick whether it is positive or negative, and then I randomly choose to prime you with a good or bad word. The results showed that people were quicker at categorizing photos when it was followed by a consistent prime. So not only will you categorize the kitten quicker when it is preceded by a good word, you will also categorize it quicker when it is followed by a good word. It was as if, while participants were categorizing the photo, their brain knew what word was coming next and this facilitated their decision.

There are at least four explanations for these results:

1. They’re real: we have previously unsuspected abilities to detect the future.

2. They’re fraudulent: Bem rigged the experiment or made up the data. I’m assuming this isn’t the case.

3. They’re wrong because of some flaw in the experiment (or in the computer programs) that made these results artifactual.

4. The results are statistical outliers that got published simply because they represent one of those cases in which we reject the null hypothesis (i.e., the hypothesis that we have no ability to predict the future), even though it’s true. This is called a “type one error” in statistics. When experimental results give such an error of 5% or less (i.e., exceed the “significance threshold”), scientists do reject the null hypothesis and claim that something else is going on (in this case, that there’s precognition). But with a threshhold of 5%, you’ll make a mistake one time in twenty. (That’s the basis of the old science joke, “95% of your experiments fail; the other 5% you publish in Nature.”)

So maybe Bem’s results represent type I errors. This is the conclusion of Psychology Today blogger Daniel R. Hawes. And indeed, the probability values in Bem’s experiments aren’t all that tiny (see his Table 7): several of them are between 1% and the critical 5% threshold. But—assuming Bem published all of his studies, and didn’t leave out the ones that didn’t show precognition—they’re consistent: the effects (though very small, about a 3% increase in “hits” over what’s expected by chance), are always in the same direction. Even though the “precognition effects” aren’t large, this consistency demands explanation.

But before we have explanation, we must have replication. Now that this result is in the open, it’s up to other scientists to see if similar studies give similar results. Only then should we start worrying about the possibility of unknown “powers.”

In a comment on the Psychology Today article, hokum-debunker James Randi has challenged Bem to meet his conditions for demonstrating paranormal phenomena, a demonstration that comes with a million-dollar prize. Randi:

I find this to be a very interesting reader response. After the usual magnificently uninformed comments: “Time is strange, gravity doesn’t make sense, and matter is mostly empty space. There is no such thing as time. Everything, what we call past, present and future, is happening in the Now” we find far more cogent remarks, along with the suggestion that author Bem should go for my Foundation’s million-dollar prize. Of course he should, but he won’t. We’ve made him the offer, many others have, as well, but he chooses to ignore it. It’s there, it’s real, the grubbies constantly claim it doesn’t exist, but it persists. Dr. Bem, give us a call. Accept the challenge, under your conditions, thoroughly fair, proper, definitive, observed and controlled, and you don’t have to invest a penny. Isn’t that attractive to you? And just think of the book sales along with the currency. Yes, a million US dollars still buys a lot… Make us all happy, won’t you? Hello…? Dr. Bem? You there…?

Do read the paper first if you want to take apart the study.