Health 26 September 2017 A new study reveals we're all a little bit delusional Delusions have a lot in common with feelings of déjà vu. Getty Sign UpGet the New Statesman's Morning Call email. Sign-up Imagine that on your way to the shops, you have a sudden feeling that it's about to rain, and voila - it starts to rain! Did you just predict the future? What if you believed that you did? Does that make you delusional? According to scientists at Yale, the answer is, perhaps, at least a little bit. That's the premise of a new paper on the science of delusion and psychosis in the Proceedings of the National Academy of Sciences. The scientists were trying to determine whether there was a relationship between delusion and what is called a "postdiction" paradigm - when people mistake a prediction for something that has already happened. The experiment the study is based on is deceptively simple. Participants were asked to look at five randomly-spaced white squares on a screen. One square, at any time, would then become red. The participant was asked, when looking at the white squares to guess which square they believed would become red. As the square becoming red was completely random, the participant had a one in five chance of predicting the square correctly. The participants were then asked to report to the researchers whether they had predicted correctly. The scientists could control when the random white square would turn red. If the white square turned red within 250 milliseconds, the participants were more likely to say they had made an accurate prediction. If the white square changed colour after 250 milliseconds, the participants reported accurate predictions - ie they were right one out of five times. So what's so special about the white square changing colour within 250 milliseconds? This phenomenon is called an “illusory reversal of thought”. The square is actually already changing colour while the participants are making their prediction. They think they have correctly guessed which square has changed colour, but actually their subconscious has just processed which square changed colour. The participants, though, believe that they have made a prediction. As Dr Adam Bear, the lead author of the paper tells me, "a perceptual event that seems to occur later in consciousness (a square turning red) biases a prediction that's experienced earlier in time". In other words, did you really predict that it would rain, or did you first subconsciously feel rain drops, and then consciously make the prediction that it would rain? You didn't guess that it would rain! It was already raining, and it just took you a while to realise. Bear compares it to the "experience of déjà vu" . You might feel like you are anticipating everything that is happening in the moment. "But that's only because a subconscious memory system has already processed what's going on and that information hasn't yet reached your consciousness." The participants were also asked to complete a 21 item Delusions Inventory (PDI) questionnaire which measures a person’s tendency to be delusional. It asks such questions as whether “you ever feel as if people are reading your mind?” While most people will resolutely answer "No", it should be noted that psychosis is a continuum. We are all prone to a few delusional ideas - just look at Donald Trump. In the experiment, those who more likely to say that they had predicted which square would change colour correctly (when in fact they had just observed the square change colour), were also more likely to score higher on the Delusions Inventory. Bear says that believing these types of errors are the "kind of thing you might expect would predict certain delusional beliefs, particularly about clairvoyance, telepathy and grandiosity". This effect could be due to a number of reasons. Studies have shown that those who are more prone to delusions are more ready to jump to conclusions based on weak evidence. This perceptual timing illusion may accentuate delusions of control. The latter is best explained by our inability to tickle ourselves, as our brain knows the action is self-initiated. This is the case even if a robot arm mimics your actions and tries to tickle you - it can't. Your brain knows who's in ultimate control. Scientists think we laugh when tickled in order to diffuse the tension and show our tickler that we submit. However, a robot arm can tickle you - so long as you delay its action after you have instructed it what to do. This delay makes the brain think the robot arm is not under your control. Timing is everything. The scientists hope that if these types of errors are more present in people before they start expressing delusions, their five white squares test could be used to identify those at risk of psychosis. This could be a very significant achievement. Not only is the test inexpensive, it can also be done easily online. The earlier people are identified, in psychosis especially, the more effective intervention treatments can be. › They may have a formula, but Nancy Meyers films are irresistibly charismatic Jason Murugesu is a postgraduate student in science communication at Imperial College London, and a former Wellcome Scholar at the New Statesman. Subscribe For more great writing from our award-winning journalists subscribe for just £1 per month!