This is fascinating!  One of the first things I remember hearing Dave Snowden speak about is how people make decisions.  According to cognitive science we only have a very small percentage of what’s in our visual range in sharp focus at any given time.  We see through a series of spot observations and fill in the rest based on past experience.  This often leads us to physically not see things that don’t fit our expectations or patterns.  I remember when I first heard this I started wondering what I’m NOT seeing!  How much of reality am I missing?

This video illustrates this theory perfectly.  In essence over 70% of the people in the experiment completely miss seeing a change that should be perfectly obvious.