.... But did you? Is it possible your eyes played tricks on you? With certain environmental and physiological factors, the answer is yes. Misperception can be a touchy subject, but those who are interested in investigating paranormal claims should have a basic understanding of common causes contributing to such experiences.
It is understandable for people to become defensive when presented with the possibility that they did not actually experience what they thought they did. It is extremely uncomfortable to know that we cannot trust our own senses. After all, we rely on our senses to inform us about our environment as well as our status in it. Some may be concerned that misperception might be sign of a mental or emotional defect. This is untrue. If someone experienced a hallucination because they were extremely dehydrated, is that a mental defect? Of course not, it is a physiological issue.
Sometimes, under certain conditions, our own physiology fails us. When visual and audial information is inadequate for the brain to interpret, it relies on our memory and experience to fill in the missing data. Unfortunately, sometimes that process results in misinterpretation.
Many of us are familiar with the term matrixing, also known as paradoelia. Our brain is programmed to recognize patterns. When processing information, it will try to make a pattern out of random data. A visual example of this is when we find shapes in the clouds. Our brain is especially fond of finding faces which causes some issues with so-called ghost photos. People will see "faces" in curtains, window reflections, etc. and mistake it for being paranormal. Paradoelia also occurs in how we process audio. One very common example is when one is taking a shower and think they hear the phone ringing, but it isn't. We hear a sound at a certain frequency, and again our brain runs through our memory files to identify it. Sometimes it picks something else that is at a similar frequency, in this case a phone ringing, instead of the reverberation of the running shower.
The physiology of our eyes and how they function often plays a part in misperception. It is our central vision (produced by retinal cone cells) that provides details of what we see. Our peripheral vision (produced by retinal rod cells) excels at perceiving movement, but lacks details and color. Our brain then helps "fill in" the missing details so we don't notice. Sometimes the brain substitutes images from our memory banks. Unfortunately, the substituted image may not be accurate and what is a simple shadow may become an apparition. When we turn to look at it head on, it vanishes because our central vision now processes the details, and the substituted image our brain created is no longer needed.
Another misperception is a product of a common optical illusion. Certain patterns, such as alternating black and white stripes, cause a motion illusion known as the peripheral drift illusion where peripheral vision sees movements in such patterns. So banisters, blinds and shutters all have the potential to cause this effect.
Low light conditions amplify these phenomena. Our eyes aren't designed well for night vision. It takes our eyes about 30-45 minutes to adjust see as well as we can in the dark. Since our retinal cone cells don't function well in the dark, our central vision will be poor and we have to rely on our peripheral vision. And because our peripheral vision lacks processing details and color well, this poses significant potential for misperception. In dark or low light conditions we don't interpret the shape of objects as accurately, we don't see color well which may cause objects to look like shadows or even white lights, and we have poor depth perception. Another optical illusion which can occur in dark conditions is autokinesis: if you stare at small objects for too long, they appear to move. This can also occur if you stare at lights, such as those produced by LED displays. As mentioned before, our peripheral vision's strength is detecting movement. However, without the detailed central vision functioning well, our ability to see exactly where the moving object is will be poor. It is not difficult to understand how easy it is for misperception to occur. Add suggestibility to the mix and you have a recipe for seeing ghosts. Another possible issue to be aware of is that sitting in total darkness for a prolonged period of time is a form of sensory deprivation which can also cause mild hallucinations.
Hallucinations are often associated with drugs or mental illness, but they also occur because of fairly common conditions. People might think hallucinations are just limited to "seeing things" that aren't there in reality. But hallucinations can be visual, auditory, olfactory, tactile or a combination. There are physiological conditions that can cause any healthy, sane person to hallucinate. For example, fatigue, sleep deprivation, stress, and dehydration can cause hallucinations.
Certain environmental factors also can be attributed to inducing hallucinations. Prolonged exposure to high electromagnetic fields may trigger hallucinations and it has been reported that some people who may be more sensitive to high electromagnetic fields also experience feelings of being watched, anxiety, headaches and even tingling of the skin. Other possible triggers include prolonged exposure to significant levels of radon, mold or carbon monoxide. Obviously, such conditions can be found in homes and should be evaluated where there are claims of paranormal activity.
Infrasound is another environmental contributor of hallucinations. Infrasound occurs at a frequency below 20 Hertz. We don't hear it, but we can still perceive it. Infrasound not only is known to cause visual and auditory disturbances and hallucinations but also causes feelings of dread, anxiety, nausea and "heaviness" of the atmosphere. Obviously this can be misperceived as something paranormal. There are many common causes of infrasound, both from man-made and natural sources. Trains, heavy traffic, heavy machinery, and industrial plants all are sources man-made infrasound. Natural sources include thunderstorms, waves crashing, running rivers, and fault lines. It is important to note that basements act like resonance boxes, amplifying sounds, including infrasound. Same goes for large box-like buildings such as hospitals, schools, warehouses and prisons. If they are abandoned and mostly empty, this obviously increases the reverberation within the structure.
Some of the most common claims of paranormal activity involve people waking in the middle of the night to see a figure standing by their bed and then it vanishes. While this is certainly a startling and disturbing experience, there are scientific explanations which have been observed in sleep laboratory studies. There are a form of hallucinations that are associated with fairly common sleep disturbances, specifically when one part of the brain is in a waking state while another part is in a dreaming state. Hypnagogic hallucinations occur when a person is falling asleep and hypnopompic hallucinations occur as a person is waking up. Common examples of such hallucinations included feeling touched, hearing someone speaking (most commonly one's name being called), feeling a "presence" in the room, seeing gray or light "blobs" levitating in the air, smelling smoke or perfume, and as mentioned before, seeing a person or other kind of entity (i.e., aliens or demon) in the room. Fatigue, sleep deprivation, change in sleep patterns, some medications, and stress, are all factors that increase the odds of having such an experience. This is why I think so many hotels are "haunted". Many people get stressed and fatigued from their travels, and tend not to sleep well in strange surroundings. This presents conditions that can trigger hypnagogic and hypnopompic hallucinations. As someone who used to suffer from this type of sleep disorder as a child, I can assure you that the experience feels very real.
A related but more frightening sleep disorder is sleep paralysis. In addition to the hypnagogic/hypnopompic hallucination, the subject is also unable to move their body. They feel like something is holding them down or sitting on their chest. In some severe cases, the hallucination takes form of a paranormal entity, such as a ghost, witch or demon who is assaulting the subject. The subject may try, but cannot speak or cry out. Then after a few minutes, both the paralysis and "entity" vanish. This disorder certainly fits the profile of the incubus/succubus or "night hag" phenomenon reported over the centuries.
While the paranormal may exist, is important that paranormal investigators are aware of and are able to identify common probable causes of misperception. They might not help the client get rid of a ghost, but they might give them piece of mind by providing alternative explanations for their experiences. Also, when investigators are able to rule out such explanations, what is left might be truly paranormal.