From Psychology Today:
Predictable events are easy for the brain; unpredictable events require more effort. “Our expectations for what we’re going to perceive seem to be a critical part of the process,” says Greg Hickok, a neuroscientist at the University of California, Irvine. “It allows the system to make guesses as to what it might be seeing and to use computational shortcuts.”

For the full story, please visit http://www.psychologytoday.com/blog/brain-waves/201411/behind-the-scenes-our-senses-part-one-perception.