Pareidolia poser

# Pareidolia poser

The entire universe in blog form
April 21 2009 7:26 AM

# Pareidolia poser

Question for you: which of these two images shows dots that are placed at random, and which does not?

Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!

The problem with questions like this is that you already know it's the one on the left that's random, and the one on the right isn't, since you know I'm trying to trick you. But what's going on?

Our brains love to find patterns in random noise. Look at the clumping of the dots on the left; surely that's not random? But it is. The distance between dots will average out to some number, but statistically you expect there to be some deviation from that average, so that some dots will be closer together (making clumps) and some farther apart (making voids). That's what's happening on the left.

On the right, the random pattern that was generated was modified so that the dots would not be too close together. If a dot's position was found to be too close to another, its position was redone until it was a minimum distance from all other dots. What's left is a pattern that we think looks more random, but is in fact highly non-random.

A more detailed explanation of these images is at the blog In The Dark, and he uses it to talk about galaxy distributions. However, it also tells us a lot about our brains. We are instinctively lousy at statistics.

Another great example is this one: imagine you flip a coin ten times, and you keep track. Which of these sequences is more likely?

HHHHHTTTTT

or

TTHHTHHTTH