With current equipment and technology, paranormal researchers can double check themselves - disproving ghostly flashes as a car's headlights and a man's humming as the air conditioning kicking on. The apparition you swear you saw turns out to be your own shadow. The ethereal whispers behind you were a team member muttering under their breath. Human senses are fallible and open to suggestion based on previously held fears, preconceptions, and expectations. So if we're so easily deceived by our own eyes and ears, can you trust yourself?
The short answer: No.
A longer answer: Not only can you not trust your eyes and ears, even your memory is faulty. Need proof? Simply look at the many different ways our memories can betray us.
The Mandela Effect (False Memories)
The Mandela Effect is a collective misremembering of a fact or event. The term "Mandela Effect" was coined by self-described paranormal consultant. Fiona Broome, who first became aware of the phenomenon after discovering that she shared the false memory of Nelson Mandela dying during the 1980s with many other people. Another well-known example of this is the book series The Berenstain Bears. A large collective remembered the name as The Berenstein Bears, which generated a lot of online mayhem.
According to Scopes, a leading psychological theory about the Mandela Effect holds that memory is constructive, not reproductive - i.e., the brain builds memories out of various bits and pieces of information on the fly as opposed to playing them back like a recording. They can be distorted by any number of factors, including bias, association, imagination, and peer pressure. The list of psychological and social factors that can disrupt and distort recollection is very long indeed.
In paranormal investigations, whether it be by professionals or newcomers in the field, there are many instances in which false memories can throw a wrench in the machine. A group of four researchers might recall an event four different ways. It's not until they go back to the footage and see what was recorder that they know who's truth (if any) is the actual truth.
If you thought that four people having four different recollections of transpired events was frightening, memory imprinting might keep you up at night.
Think of this scenario: You remember going to the fair with your cousin when you were young. You can still feel the wind blowing your hair back as you sat on the rides. You recall the taste of the cotton candy you ate then regurgitated back up after spinning too many times. You remember the lights, the sounds, the smells. Then you come to learn, you never went to the fair with your cousin. In fact, you've never met your cousin. The memory that you remember so vividly was not your own - it was your dad's. He used to tell you the story of he and his cousin going to the fair. You adopted the story, and grew up wholeheartedly believing and remembering the events. But they never happened to you. This is memory imprinting.
If there's one thing that makes one question the validity of one's own mind, it's knowing that some of your memories may not actually be yours.
Hive Mind Mentality
A group of five people enter a spooky building. Four of them are skeptics, simply there to prove how tough they are or make fun of any "scaredy cats". One of the group members is convinced there are demons lurking in the shadows of this place, vocal about their bias. As the group walks through the rooms, this person expresses their fears and hesitation to the rest of the group continuously, and it begins to rub off onto the others. By the time they're halfway through the building, they are all terrified of the specters that must be waiting around every corner. They think they hear a sound behind them and scatter. Outside, they will all distinctly remember how frightening the place was, what they heard, what they saw. This is one example of a hive mind.
A hive mind can be described as a unified consciousness formed by a number of individuals, the resulting consciousness typically exerting control over its constituent members. In the example above, fear spread from one person to the entire group, causing all of them to be hesitant about the building. Nothing needed to happen to make them all afraid. One person just needed to give them the idea.
Just as one person's mood can affect others, so too can their recollection of events. Using the same example, let's say one of the group members points to a shadow and swears it looks like a man staring at them. They hear the noise and scatter. Outside, two of the people say they saw the man move. Then the third says they saw the man move and know he was the one that made the noise. By the time their discussion is concluded, they all distinctly remember seeing a man moving inside that building. They're all terrified by this event that obviously happened since they all remember it. But did it? Or did they fool themselves into thinking it did? That is hive mentality.
Memories - can you trust them? If we look to the Mandela Effect, false memories, memory imprinting, and hive mind mentality as examples, it's pretty clear. When doing any type of scientific research, paranormal or not, you should never trust your own senses. Humans are too easily deceived by their own minds, tricked by previously held beliefs, fears, and expectations. In the field of paranormal investigation, technology is the only thing we can rely on to keep us in check (until the day it turns on us).