According to the wikipedia , the term “cognition (Latin: cognoscere, ‘to know’) is used in several loosely-related ways to refer to a facility for the human like processing of information, applying knowledge and changing preferences.”
Here are some interesting links that you might like to explore:
You can view some of the experiments carried out by Daniel Simons and Chris Chabris in the area of visual cognition here.
Here is an example of Change Blindness. According to the site, ‘naive observers notice such changes about 30 percent of the time’ (Naive – I take it, means an average observor!)
Another great site on Cognitive Psychology is maintained by Dave Munger and Margaret P. Munger.