Take a look at the two photographs above.
The top one shows a word that’s upside down and that’s indented into a surface.
The bottom one shows a word that’s the right way up and that’s raised above the surface.
Okay, I know you’re not stupid. You realise that they are both the same photograph, with the top one upside down. (It’s a detail of a traditional red British post box by the way.)
But you’re not clever enough to see the word on the top photo as being anything other than indented, are you? Even though you know that it’s raised.
The reason for this is quite straightforward. It’s all to do with the lighting. In our everyday world objects are normally lit from above – because the sun shines in the sky and not out of the ground. In the case of the top photograph the lighting effectively comes from below. However, we don’t interpret it like that, due to the simple fact that being lit from below is a very unusual way for objects to be lit. We assume that the light in the photo is coming from above, as usual. In that case, the bright highlights and the shadows on the letters could only be where they are if the surface is indented – so that’s what we interpret it as.
What can we learn from this observation? We learn, amongst other things, that we tend to see what we expect to see. And we learn that we interpret things so that they fit in with our experiences and our expectations. This isn’t such a bad thing quite a lot of the time. In fact it’s a good thing. If we didn’t do it we’d have to go around analysing absolutely everything from first principles as though we’d never experienced anything before. We’d never get anything done. But the tendency can be an impediment when we try to make sense of things that are slightly beyond the realms of normal day to day existence – it has implications beyond such mundane things as upside down photographs.