Mind Hacks: Hack #102 : Alter Input With Expectations

This Figure (pop-up window) shows a classic example of how our perception is affected by what we know [1].

If you haven't seen this before you might not spot at first that it is a dog in the snow. Once you've seen it, you can't un-see it. It's not a conscious decision on your part; rather, your perception is now dominated by the top-down information about how this stimulus is organized. If you were just using bottom-up information, the picture would remain a picture-without-any-interpretation-a collection of light and dark splodges. But because you now know that there's a dog in the picture, you brain imposes that knowledge on our perception and you can't help but read the picture that way.

How it Works

So we're always trying to fit what we're sensing to what we know. If we just used bottom-up information only - trying to deduce what we are seeing without any expectations and assumptions - it'd be too ambiguous and too slow. But if we just used top-down information we'd only see what we already know-there'd be no surprises and we'd get caught out whenever things differed from our expectations.

You can see your top-down processes at work best in situations where the bottom-up processes are weak. With vision this might be in the dark, or where you only glimpse something or someone for a fraction of a second. In hearing this might be where background noise is loud. Poor resolution, brief or noisy information tips the balance in favor of top-down information. What we see comes to reflect more of what we already know and what we expect. Hence we see things in the dark: our brains fill in what is most likely there, what might be there, or what we fear could be there, based on small clues from what actually is perceivable there.

There's a balance between experiencing the world just as it is without any interpretation and experiencing the world just using expectations. Neither extreme is possible; it always has to be a compromise. Looking at the extent of physical feedback looks in the brain, it turns out the balance between working out the universe from first principles every time (bottom up) and imposing our expectations on what we perceive (top down) is ever so slightly in favor of bottom up. In terms of connections, it's 55% vs 45%.

Mind Hacks: Hack #102 : Alter Input With Expectations