Some people try to talk to ghosts by getting together around a table in a dark room. They call such a meeting a séance. The leader of the séance is called a medium. A medium is someone who says he or she can get ghosts to come to the room to give signs to living people that the ghost is real. These meetings never take place in broad daylight. Scientists who have looked into séances say that they are held in the dark because it is easier to trick people that way. The medium or his assistant can produce objects, move things, or make noises and speak in a mysterious voice, while the others can't see what anyone is doing. Many mediums have been caught cheating.
Séances were popular in the 19th and early 20th centuries, but today many people who say they are mediums don't use any props and work in a well-lit studio or on a stage. They don't have their ghosts ring bells or float things across the room, as was done in séances. Today's mediums just say things, claim they are getting messages from the dead, and wait for others to make sense out of what they say. A medium might say to an audience 'somebody's grandmother is here.' It is up to people in the audience to figure out what the medium means. One person might be young and think the medium means that his grandmother's ghost is in the room. Another might be old and think he means her granddaughter's ghost is in the room. If one of the people in the room speaks up, the medium will say something else and wait for the person to make sense out of it. Scientists call this process of making sense out of questions or statements raised by a total stranger subjective validation. Many people come away from such meetings believing they have been in contact with the ghost of a loved one. Many others think the medium is just playing with people's emotions and isn't getting any messages from the dead. Here is a video of James Van Praagh, one of the more popular mediums performing today. Judge for yourself whether this fellow is actually communicating with spirits.
What does science have to say about today's mediums? Some have been studied and caught cheating, but it is impossible to prove that dead people aren't making noises that some mediums hear. We have the mediums' word for it, but if they are cheating their word is worthless.
If you think you've seen a ghost, you are not alone. Many people think they've seen ghosts. Most likely what happens when a person sees a ghost is that the brain takes whatever fuzzy information it gets from the eyes, ears, and other senses and thinks there is some sort of being out there that is intentionally moving the way it is or making the sounds it is making. We call beings that can direct their own movements intentional agents. Humans have a natural bias called intentionality bias. It is common for humans to think that objects that are not agents, such as branches of trees moving in the wind, are intentional agents when they're not. Once you know that what you saw and heard was the wind blowing some branches, you stop thinking of ghosts. But if you never get a chance to see clearly what it was that your brain turned into a ghost, you can't be sure that what you saw wasn't a ghost. What you saw, though, was probably created by your imagination. You might say that when you are scared by seeing a ghost, you are scaring yourself. Why? Because your brain is probably fooling you and you are not seeing a real ghost out there in real space.[/revised]