Wednesday, 6 November 2013

Fox ghost!

Night foxCan prolonged staring at something in low light trigger misperception? This was what I speculated yesterday when looking at the 'psychomanteum effect'. This raises two obvious questions - is there any evidence that this actually happens away from a psychomanteum and how would it even work?

Oddly enough, I do have some experiences which might be explained in the way suggested. I am interested in natural history and am always on the lookout for animals in the wild. One thing I do regularly is watch for foxes after dark. As any field naturalist will tell you, one of the best ways to spot animals is to look for movement in an otherwise still scene. It can be difficult to spot a static animal as they often blend in with their surroundings. But as soon as they move, they become easier to spot. So, to look for foxes I carefully watch a poorly illuminated area where I've seen them before, waiting for any movement that might indicate their presence. And the technique works well!

But I've noticed something odd while watching these static night scenes. I frequently see apparent slight movements, but when I focus on the moving 'object', it turns out there is nothing there! These 'objects' appear out of nowhere and disappear once I pay them close attention. A ghost fox, perhaps? Well, in fact, it looks just like a classic case of misperception! I had previously dismissed these occurrences as simple 'low light misperception' but now I see there is actually something different going on.

Typically, misperception occurs when you first look at an object, whether it is a familiar or unfamiliar one. As you pay closer attention to it, the misperception dissolves. The 'ghostly figure' becomes the poorly-seen tree stump it really is. In the 'fox' example the misperception occurs in a scene that has already been seen properly and all objects correctly identified visually. So why do these misperceptions occur after the scene has been stared at for a while?

I think that if you stare at a static scene for long enough, your perception system may reevaluate what it seeing and try new visual substitutions for things previously identified. But why? Well here's a thought. In everyday life we almost never stare at unchanging scenes. There is almost always change in our visual fields, even if it is just us adjusting our viewpoint of a static scene. If our perception system is adapted to this constant change, which seems highly likely, it may be continually 'guessing' at what it is seeing, even when there is no actual visual change occurring. And when the viewing conditions are poor, this may lead to 'new' guesses from time to time.

But can't the perception system simply remember what is there, as nothing has actually changed? Well, as I speculated recently (here), it may be that our perception system does not remember its previous mistakes. Maybe the 'psychomanteum effect' shows how this works in more detail. If you stare continuously at an unchanging scene, you are only paying attention to any one object in it at any one time. The rest of the scene is maintained by memory. But maybe, after a few minutes, that memory 'expires' (like short term memory) and the whole scene is re-evaluated, with some inevitable mistakes in poor viewing conditions. More clues, perhaps, to how misperception works and how some reports of anomalous phenomena are generated. I also wonder if looking for wildlife is why I am more sensitive to noticing misperceptions than most people.

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