One of our favourite videos to show in workshops is this selective attention test, which highlights 'inattentional blindness'. Watch the video and see how you get on. You can also try this test of auditory awareness if you have some headphones handy.
As Christian Jarrett explains in his book Great Myths of the Brain, so much goes on in the world around us that our brains, if they tried to process everything, would be paralyzed by data overload. Our brains, in an effort to combat this, employ selective attention by screening out various kinds of sensory information.
As Jarrett notes, "These attentional limitations could have serious real-life consequences - just think of the jobs that depend on the human ability to notice what's going on, from air-traffic controllers to radiographers."
Our limitations as humans mean we miss out on all sorts of other information too. For example we can't hear high pitched sounds or see infra-red waves. We also have a visual blind spot, which you can 'see' for yourself here. As Jarrett points out, "the existence of this blind spot means that wherever you look there is a permanent gap in your view of the scene."
It turns out we often have problems interpreting colour information too, as you'll know if you followed the numerous articles about The Dress.
There are many more examples in Jarrett's book, and his analogy is that the brain creates for us an incredibly believable virtual reality experience. As he concludes:
"From a user's point of view, this is a good thing. Our perceptual experiences are subjectively compelling, and from an evolutionary perspective, they served our ancestors well in terms of survival. The downside is occasional over-confidence - when what we experience is not what is there. This can manifest itself in the fun of a psychologist's illusion or the tragedy of an accident."