From Scientific American:
There seems to be a simple way to instantly increase a person’s level of general knowledge. Psychologists Ulrich Weger and Stephen Loughnan recently asked two groups of people to answer questions. People in one group were told that before each question, the answer would be briefly flashed on their screens — too quickly to consciously perceive, but slow enough for their unconscious to take it in. The other group was told that the flashes simply signaled the next question. In fact, for both groups, a random string of letters, not the answers, was flashed. But, remarkably, the people who thought the answers were flashed did better on the test. Expecting to know the answers made people more likely to get the answers right.
Our cognitive and physical abilities are in general limited, but our conceptions of the nature and extent of those limits may need revising. In many cases, thinking that we are limited is itself a limiting factor. There is accumulating evidence that suggests that our thoughts are often capable of extending our cognitive and physical limits.
More here.