Seeing is believing
The skeptical often discard a new idea by claiming "I'll believe it when I see it!". I'm sure most of us tend to consider seeing something with our own eyes as the crucial step in confirmation. In fact, we naturally tend to trust that what we see through our eyes is precisely what is in the world around us.
Despite this, there are some pretty convincing optical illusions out there.
In the images above respectively, there is no bowing of the lines, the centre circles are the same size, the horizontal lines are straight and the rectangles are the same size and shape. Images are from Akiyoshi's illusions pages
In these circumstances our faith in our eyesight fails us, yet we can generally explain them away as unrealistic contrivances. Since I began painting the house however, I've gradually become less and less confident of the ability of my eyes to deliver a reliable picture...
The problem in particular, is with colour. Colours not only shift and squirm in response to ambient light, reflections and angles, but the ability our eyes to recognise complementary or contrasting colours in different situations is probably much worse that you expect. Take a look at these examples. And take the time to convince yourself of what you're seeing:
Squares A and B are the same colour. From Wikipedia. Conclusion: we can't tell shades of grey apart.
The centre tile of the top and front faces are the same colour. From R. Beau Lotta's Lotto Lab. Conclusion: we can't tell orange and brown apart.
The squares on the top face are the same colour, and in fact, are the colour of the islotaed squares in the bottom pictures. From American Scientist. Conclusion: we can't tell much about colours at all.
Now to finish off this soul damaging slap across the face, have a squiz at this innocuous looking example.