Imperception – when things simply vanish

This time of year (in the UK anyway) you can usually experience imperception – a type of misperception (see here). If you look up into the sky, particularly on sunny day, you may spot a swift or two cruising around high up, barely visible.

If you follow the swift for a while, and it is distant enough, you might notice that it may vanish completely, instantly. It might well re-appear later, as if from nowhere, nearby in the sky. The bird hasn’t really disappeared, of course. So, what’s going on?

What happens is that your brain simply can’t make out what the distant, vague object is any more and simply stops seeing it. Vision is only partly a function of the eyes. Most of the perceptive process actually happens in the brain. When you see something, in poor viewing conditions, your brain may guess what it is and substitute in an object from your own visual memory rather than show you what is actually there – misperception. But it may, instead, simply decide to give up and show you nothing instead. It substitutes in a bit of nearby ‘background’ where the object should be. In the case of the swift, it shows you blue sky where there is, in fact, a bird.

Of course, people don’t often report ghost birds! But suppose you saw the distant figure of an obviously real human being walking slowly away from you. You might have a completely unobstructed view, with no bushes, trees, buildings etc nearby. And yet, suddenly, the figure has gone, even though you were watching it continuously. You might either conclude the person fell down a hole or that you were, in fact, watching a ghost. Witness reports of distant figures seemingly vanishing, when there is no obvious place for them to be concealed nearby, are not uncommon and they tend to be reported as ghosts. I suspect in many cases they are actually cases of imperception.

Note that the photo shows a buzzard, not a swift, though I’ve seen them vanish in a blue sky too, despite their size.