You are all missing the point. This is not about whether someone believes in ghosts, or saw a ghost, or thought he saw a ghost. This is about whether someone is seeing something right now, whether a ghost or a tree or Mickey Mouse, in a spot that you can clearly see is empty. OK, let me explain because I see where this is heading... Hallucinations are on a continuum with ordinary sensory experience. We all have thought one time or another that we saw something from the corner of our eye, thought we heard someone call our name, etc. This is quite usual: sensory perception is complex, and our senses are far from perfect. Our brain has to filter a lot of crap out of a stream of rapid impressions on an ongoing basis. It uses "reality testing" for this: basically a framework of past experience and knowledge to audit and interpret what we (think we) see, hear, smell, touch etc. mediated by the frontal and temporo-parietal lobes of the brain (it is largely a whole-brain process). As such our brain is pretty good at "filling in the blanks" and making sense of ambiguous information. We are wired to pick out recognisable shapes, patterns, sounds etc. from ambiguous sensory noise. Sometimes however, our brain guesses wrong and we experience what we call an "illusion". Those optical illusion pictures which "trick" the eye are an example of basic visuo-perceptual processing "guessing" it wrong. We can also have other "tricks of the mind" in which we think we saw or heard or felt something, and quite biased memory recall of such experiences. This is OK as long as we realise we are perceiving it wrong. We have many failsafes after all; if we perceive something that doesn't fit in our reality testing framework we do a double-take: we look or listen again, to make sure. Our brain's reality testing circuits frantically looks for explanation. Sometimes it cannot find one, but it knows (or rather, our mind knows) that what we are perceiving is not "normal". It can be unsettling to live with this discrepancy between what you perceive and how you know things are supposed to be, until you find a satisfactory explanation. Many people do, in fact, hear voices, or see or smell or taste things (e.g. synaesthesia) and know that they are, in fact, experiencing glitches in sensory perception. These can often have meaning and structure and if they don't cause too much bother, people just live with them. If our belief system incorporates ghosts or deities or other supernatural phenomena, our brain (and more consciously, our mind) will be happy to fit certain incongruous sensory experiences within that, and stops looking for alternative, more mundane explanations. That doesn't mean you see a ghost, it just means that you think you see one. Again, no problem depending on what that means for you... I'll come back to that. Reality testing is suspended during dream sleep, which is why we readily accept the most bizarre things happening in our dream without us saying: "hey, I must be dreaming". Being a complex, whole-brain process, reality testing and interpretation it is also disrupted during brain injury, intoxication, psychosis, basically anything that disrupts normal brain processes. In those cognitive states we are more likely to get confused by our sensory experiences as we find it difficult to "reality test" and make sense of them, particularly in a time-pressured, on-the-fly process because we are cognitively slowed as well. So what does that get us? That depends on a person's belief system: someone who believes in ghosts is more predisposed to the experience of seeing them (we see what we think we see, remember?). Those who don't are more likely not to see them but to continue looking for alternative explanations that fit in their belief system. But the further our sensory experience moves away from normal everyday perception to out-and-out hallucination, the more likely brain processes are to be disrupted somehow. Not necessarily in a big way, as we know from e.g. synaesthesia and dream-state narcolepsy, but if the hallucinating person is also incoherent, confused or disoriented, then you really want to look at their brain. And even fairly harmless brain glitches can be the early warning signs of a brain tumour, transient ischaemic attack, or other serious brain conditions... Back to believing in ghosts. Delusions are also on a continuum with more ordinary beliefs. What makes delusions delusional, rather than beliefs, is the strength with which they are maintained in the face of all contrary reason or evidence. So if a person believes in ghosts, and therefore (thinks he) saw one, that's not a problem in itself. If, however, he now ties his family to the bed and proceeds to exorcise them, it is. Now most people who believe in ghosts are not that irrational. They believe, but they can still reason about it. Same as with religious beliefs, belief in fate, and even scientific beliefs. As long as you can be rational about them, and modify them in the face of the available evidence (e.g. "OK, I realise that this was a reflection of the light and that I did not see a ghost this time"...), then you are not delusional. If however you maintain that you can see a ghost right now when people around you cannot, then you are hallucinating or delusional. Either requires some further exploration to find out where on the continuum that person is, and whether or not this is a straightforward interpretation of ambiguous stimuli within their personal belief system or not. And also, whether something sinister might be going on in their brain.
Still not convinced? OK, I once had a client who had wild day-time hallucinations (and I mean, amazing stuff). He interpreted these experiences within his belief system that he was being visited by a pagan deity. Now that's nice. Should I have respected his beliefs? Should I have respected the spirituality of his experience? It was not as if they led him to do crazy things; he was functioning quite normally after all. But I wanted to know what went on in his brain. After some neuropsychological testing (fairly uneventful) and some research I referred him to the sleep clinic for 24 hour EEG. Turns out he has dream-state narcolepsy. Not a big problem, but if evolves it could really make it tricky for him to drive or operate big power tools (a requirement in his job). However he was put on meds and his hallucinations subsided. He lucks out on his spiritual experience, but at least he can drive a car and work. And he continued taking the meds, so I think I know what he prefered. People have come with stuff like that and investigation has found temporal lobe epilepsy, brain tumours, arterial stenosis, you name it. I like to be accepting of peoples unique beliefs and experiences, but I also always like to rule out brain dysfunction. It can be a matter of life and death.
*Obvious* implies certainty. *Probably* implies doubt. "It is obvious that the security guard was probably having a psychotic episode" Is it obvious that he was having a psychotic episode, or probable that he was having one? It can't be both. He may or may not have mental health problems, or he may have actually seen what he claims. Unlikely perhaps, but who is to say?? The one thing for certain is that if you know anything about mental illness, you know better than to diagnose at long-distance.
Oh, let it go already... OK: Obvious: easy to see, understand; unambiguous Probably: likely. "It is easy to see that he probably had a psychotic episode" There, feel better now? Bickering over semantics does not constitute rational argument. I know enough about mental illness to make an educated guess. As I indicated before, that's not where you stop, that's where you start. You make a hypothesis, you investigate. Investigations are good. They remove doubt (or at least narrow down the possibilities) and stop you from jumping to conclusions. Whatever this gentleman saw, could range from a simple interpretation of an ambiguous stimulus within his personal belief system, to an out-and-out hallucination/delusion. The former is no problem; the latter is likely to have organic causes. Some of these will, eventually, kill or damage the sufferer. So rather than dismissing the security guard as superstitious, or as a nutter, or to shrug and say: "Hey, he might have seen a ghost... who knows?", you just make sure that he doesn't happen to have, say, a tumour the size of an orange growing in his temporal lobe (as happened in one case). I'm sorry if that offends the sensibilities of those who believe in ghosts, but my job is to be concerned with the living, not the dead.
