What's REALLY going on when you wake up in the night and sense a monstrous presence in the bedroom - tantalising book reveals why some believe they have been abducted by aliens or their houses are haunted

Waking in the middle of the night, with the horrifying sensation that there was an evil presence hovering behind him, 18-year-old Matt Salusbury tried to leap up and scream for help, but found himself being pinned down, unable to make a sound.

Although his tormentor was just out of sight, he sensed it was in some way skeletal, like the deadly extraterrestrial in the movie Alien, with some sort of gristle and muscle between the bones.

'I couldn't see a face,' recalled Matt, who was sleeping on a relative's sofa while travelling in the US during the summer of 1986.

'I can't recall the colour, except for the white teeth with the raw flesh of the gums around it, as if the skin of the face and lips had been peeled away.

'I closed my eyes tightly, trying to pretend I was asleep, somehow feeling that if it didn't know I was awake it might not react and might leave me alone.

Many supposed victims of alien abduction report waking up paralysed with a sense of a strange presence in the room - this sign is, in fact, a common symptom of sleep paralysis

'I remember lying there for perhaps hours before I eventually drifted off to sleep. I was absolutely terrified, perhaps the most scared I've ever been in my life.'

Although this happened almost 30 years ago, the memories are still clear in Matt's mind.

But was what happened to him quite the spine-chilling visitation that it seemed?

The answer is no. As someone who has spent the past four decades working as a professional sceptic, I have been contacted by many people who have had a similar experience.

It happens all over the world. In China, it is referred to as 'ghost oppression', while the Germans call it 'witch pressing' and the Mexicans say 'a dead body climbed on top of me'.

Sufferers are often reluctant to tell anyone else about their experience because they are afraid, with some justification, that they may be judged 'crazy'.

So they are hugely relieved to learn that their experience can be explained scientifically as an episode of 'sleep paralysis'.

It happens when there are glitches in the rapid eye movement (REM) stage of sleep, during which the muscles of the body are paralysed — presumably to stop the sleeper carrying out the actions of the vivid dreams experienced during this part of the sleep cycle.

With sleep paralysis, the mind wakes up but the body does not. The sleeper may be able to open their eyes and clearly see they are in their bedroom but remain unable to move.

Many supposed victims of alien abduction report waking up paralysed with a sense of a strange presence in the room. They sometimes also report feelings of flying through the air or seeing balls of light or dark shadows in a room with no idea of what is causing them.

All these signs are, in fact, common symptoms of sleep paralysis. In most cases, the person doesn't claim to have actually seen aliens, but some sufferers have ascribed such episodes to abduction by extraterrestrials who then wiped their memory of further details.

Further 'proof' comes from the unexplained scars and bruises that abductees find on their bodies but I suspect that if most of us examined every square inch of our skin, we would find some examples of such marks and be unable to account for how they got there. Alien abduction would not generally be top of the list of possible explanations.

This is but one example of the seemingly supernatural phenomena I look at as a specialist in 'anomalistic psychology', the study of human behaviour and experiences connected with the paranormal.

This field was once regarded as pretty much a waste of time by some of my academic colleagues. After all, they would say, we all know that ghosts don't exist and that people aren't really being abducted by aliens, so why are you interested in this stuff?

This is missing the point. I believe that the vast majority of those who claim psychic powers genuinely believe that they possess them. Similarly, many people who say that they have had a paranormal encounter are really convinced that this is the case.

You can almost always uncover a logical explanation for things that appear to be paranormal, writes Chris French

We can learn so much about the human mind by investigating what lies behind experiences that appear to be paranormal. Factors like attention, perception and memory can all play a part.

What I've also found is that you can almost always uncover a logical explanation for things that appear to be paranormal.

Take the case of 72-year-old Stephen McKears from Severn Beach, Gloucestershire. In March 2019 he was puzzled when he noticed that his garden shed was being mysteriously tidied up overnight and began to consider the possibility that a helpful ghost was responsible — a kind of anti-poltergeist who created order out of chaos.

After some months, Stephen set up a video camera to record what was happening when he left his shed. The answer came as something of a surprise: no ghost, but a tiny house-proud mouse spending several hours strenuously tidying away the objects that Stephen had deliberately left scattered around. These included not only nuts, bolts, and screws but even small metal tools.

This is a wonderful example of the phenomena that can lead someone to suspect that their house is haunted. Others include structural faults which cause draughts and cold spots, and noises caused by water movement in pipes or rats scratching.

I know from experience that if a light begins to flicker when I am giving a talk on ghosts, I am guaranteed to elicit a nervous giggle from my audience if I suddenly look puzzled and mutter: 'Oooh, spooky!'

But doing the same thing during a statistics lecture would not elicit the same response. Context is all-important.

So, too, is 'inattentional blindness' — our inability to notice stimuli that are right before our eyes when we are engaged in some other task.

You may have seen this demonstrated in the viral YouTube video in which you are asked to count the number of times people throw a basketball to each other. Many people fail to spot the man in a gorilla suit walking into the centre of the action halfway through.

Similarly, suppose someone claimed that a book shifted from one location to another when no one else was around. The suggestion that maybe they just did not observe someone else move the book would probably elicit the indignant response that they would have noticed if anyone else was nearby.

But would they? After all, lots of people fail to see a gorilla beating its chest when it is right in front of them.

Neither can we rely on our recall. One widely held misconception is that memory works like a video camera, accurately recalling every detail that we ever experience.

In fact, we process only a small fraction of the sensory information available. Our brain fills in the gap to give the impression that we have a complete mental model of the world around us. 

This 'top-down processing' can be illustrated by seeing if you can answer the following question: without actually looking at any clocks or watches, can you remember how the number four is represented on those with Roman numerals on them?

Most people confidently reply that it is marked as 'IV' and they are surprised to learn that on most timepieces it is, in fact, 'IIII.' This tendency to end up with memories based on what we think must have happened rather than what actually did happen has been demonstrated in studies in which actors have played the parts of mediums in fake seances.

In one, the 'medium' suggested the table was moving when it was not. Afterwards, one-third of the participants incorrectly reported that the table had moved. Perhaps not surprisingly, believers in the paranormal were more susceptible to this suggestion than nonbelievers.

It's a similar phenomenon with ouija boards. Why does the glass on a ouija board continue to move around the table, spelling out messages from the 'spirits', even when nobody is knowingly pushing it?

This can be explained by the 'ideomotor effect' — the influence of suggestion or expectation on our involuntary and unconscious movements. In other words, we really are pushing the glass around the table but we are just not aware that we are doing so.

It follows that no meaningful messages would be produced if all sitters were blindfolded — and that is precisely what studies have found. Many mediums and psychics rely on 'cold reading', giving complete strangers the impression that they know all about them even though they have never met them before.

One technique depends on a phenomenon known to psychologists as the 'Barnum effect'. This is our tendency to rate statements made about us as accurate, even though they are vague enough to apply to pretty much everyone.

These are statements such as 'You have a great need for other people to like and admire you,' or 'You have a tendency to be critical of yourself.'

Another trick, called 'hot reading', requires gathering information about your client in advance.

A method widely employed by fake stage psychics is to have colleagues queue up with genuine audience members as they are waiting to go in, engage them in friendly conversation, and surreptitiously feed any information gleaned back to the psychic before the show begins.

It is easy to appear to read people's minds. In my public talks, I sometimes tell the audience that I am thinking of a number between one and ten and that I'm going to send it telepathically from my mind to theirs. 

I then, apparently somewhat nervously, ask, 'If anyone thought of seven, raise your hand.' With a large audience I can be very confident that around a third of them will do so, thanks to a phenomenon known as 'population stereotypes'.

Asked to make a mental note of the first number that comes into their head, people assume this is pretty much a random process but, for reasons we don't yet understand, responses tend to cluster in predictable ways and you can be pretty sure that seven will be the most popular answer.

There are other examples of population stereotypes that could be used to fool (at least some of) the unwary that you possess telepathic powers.

Tell them your target is two simple geometric forms, one inside the other. Around 60 per cent will choose the circle and triangle. If you tell them that you are thinking of a simple line drawing, around 10 to 12 per cent will draw a little house.

It makes for an amusing party trick but some people have tried to pass it off as really involving telepathy. For example, in the mid-1990s Uri Geller took part in a TV programme called Beyond Belief, demonstrating his alleged telepathic powers by secretly choosing one of four symbols shown at the bottom of the screen — square, star, circle, and cross.

He then supposedly transmitted it to viewers who would phone in using one of four different numbers to indicate their guess at Uri's choice of symbol.

Over 70,000 viewers did so, with 47 per cent opting for the star symbol chosen by Uri. The probability that almost half of the callers chose this symbol just by chance is astronomically low.

Although this seemed strong evidence of Uri's psychic powers, the symbols presented were those used on the cards designed by psychologist Karl Zener in 1939 and frequently used to test for evidence of extra-sensory perception (ESP).

It has been known for more than eight decades that people are more likely to guess certain symbols than others, with the star being the most popular choice. It's perhaps no coincidence, then, that Uri chose the star as his 'telepathic target'.

There are other coincidences so fortuitous they seem almost magical. In the summer of 1972, for example, the actor Anthony Hopkins was signed to play a leading role in a film based on the novel The Girl From Petrovka, so he travelled to London to buy the book. Unfortunately, none of the bookshops had a copy.

Then, on his way home, waiting for an underground train at Leicester Square station, he saw a discarded book lying on the seat next to him. It was a copy of The Girl From Petrovka.

Perhaps there is something about the London Underground that facilitates the occurrence of amazing coincidences?

In another account, the journalist Simon Hoggart recalled that his wife was once travelling with a friend on a tube train and talking about the actor Richard E Grant.

The friend said she could not place him; what did he look like? At that moment, Richard E Grant got on to the train, and sat opposite them. He was holding a ticket for the same exhibition they were about to go to.

We are impressed by such coincidences because we fail to appreciate what mathematicians call 'the law of truly large numbers'. This states that with a large enough number of opportunities for an event to occur, even extremely unlikely events become probable.

For example, in the case of dreams that appear to come true, we tend not to think about the fact that pretty much everyone dreams pretty much every night.

It would be remarkable if no one ever had a dream that corresponded, purely by chance, to some unexpected event in real life some time later.

A moment's reflection will reveal that coincidence may well be a more plausible explanation than any kind of psychic link. Just consider how many people you think about in a single day.

Most of the time when you think about them, either the phone does not ring or the phone rings and it is someone else calling.

Occasionally, simply based on the laws of probability, the person calling will be the person you were thinking about and we say, 'you'll never guess what, I was just thinking about you!'.

But in fact, it would be really spooky if this never happened.

Adapted from The Science of Weird Shit by Chris French & Richard Wiseman (MIT Press Ltd, £30). © Chris French 2024. To order a copy for £27 (offer valid to April 7; UK P&P free on orders over £25) go to www.mailshop.co.uk/books or call 020 3176 2937.