Nearly 40 per cent of the UK population claim to have experienced a ghost, according to a MORI poll from the late 1990s, while a smaller but significant percentage – around a third – claim to have had some kind of paranormal experience. In this talk for the Edinburgh Skeptics on the Fringe, professor of anomalistic psychology (basically ‘weird stuff’) at Goldsmith’s University, Chris French, explains what might be going on from a rational, science-based perspective.

What follows is a straightforward explanation of several normal physical and psychological phenomena that cause people to believe they’ve witnessed some kind of paranormal activity. For example, many reports of poltergeists turn out to be straightforward hoaxes, notably including the founders of the modern spiritualist church, Maggie and Kate Fox, and the Amityville Horror which was popularised in a novel and films. Both have since been roundly debunked but still persist in popular culture as real.

One major cause of haunting stories is the poorly-understood condition of sleep paralysis, where a person partially wakes up during REM (dreaming) sleep. It’s remarkably common, and somewhere between eight and 40 per cent of the population are thought to experience it. Normally, the body is paralysed during REM sleep to prevent us acting out the physical motions of our dreams, so unexpectedly waking up in this state can be terrifying and disorientating. Even more distressing is the accompaniment of ‘dream hangovers’, such as visual, auditory and physical hallucinations. Given the similarities of these reported experiences across cultures, variously attributed to everything from sex demons (incubi and succubi) in Europe to the souls of unbaptised children on St Lucia, it’s likely that sleep paralysis is a much more common cause of ghost stories than previously realised.

We’re also hugely prone to creating things that simply aren’t there, such as seeing the face of the Virgin Mary in a cheese sandwich or inferring a ghostly whisper in crackling static. Alternatively, we fail to notice the blindingly obvious explanations for seemingly strange things right in front of our faces, as shown by the clever ‘Gorillas in our Midst’ study.

As French explains, the most important requirements for seeing ghosts are context and belief. You’re much more likely to spot a spectre if you’re a strong believer creeping around a reputed haunted house than a skeptic strolling through Sainsbury’s. But if ghosts are real, why should there be a difference? Like Fox Mulder in the X Files, some people just want to believe, and all too often their brain tricks them into thinking that they do. There is no cure, but approaching all paranormal claims with a broad, evidence-based and skeptical mindset will undoubtedly help.

- KA

Edinburgh Skeptics in the Pub is hosting Skeptics on the Fringe, Undiluted Brilliance, with a different speaker every night until August 28th, at 19:45 in the Banshee Labyrinth on Niddry Street - http://www.edinburghskeptics.co.uk/events-calendar/

Goldsmiths Anomalistic Psychology Research Unit: http://www.gold.ac.uk/apru/

The Fox sisters and the rap on spiritualism: http://www.smithsonianmag.com/history/the-fox-sisters-and-the-rap-on-spiritualism-99663697/?no-ist

The Amityville Horror hoax: http://www.snopes.com/horrors/ghosts/amityville.asp

Information about sleep paralysis – NHS Choices: http://www.nhs.uk/conditions/Sleep-paralysis/Pages/Introduction.aspx

The invisible gorilla experiment – an example of inattentional blindness: http://www.theinvisiblegorilla.com/gorilla_experiment.html