Clear descriptions of what we now call post-traumatic stress disorder date from at least as early as the U.S. Civil War. (source)

According to a 2008 National Institutes of Health study, 9.4% of people between 20 and 29 years of age had Narcissistic Personality Disorder at some point in their life.

It is widely believed that you shouldn't change your initial answer on multiple-choice tests, as you're more likely to change a right answer to a wrong answer. Actually, over 60 studies suggest the exact opposite: When students change answers on multiple-choice tests, they're two to three times more likely to change from a wrong to a right answer than from a right to a wrong answer. (source)

Information processed by its meaning is better retained than information that is merely repeated over and over. (source)

Psychologists have taught pigeons to tell the difference between paintings by Monet and paintings by Picasso, and between musical compositions by Bach and musical compositions by Stravinsky. (source)

U.S. census reports indicate that a disproportionately large number of people live in places with names similar to their first names. For example, there are more Georges in Georgia, or Virginias in Virginia, or Louises in Louisiana, than would be expected by chance. This effect also applies to names of cities or towns. It appears to be caused by people with certain names moving to places with similar names (as opposed to parents naming their children after their place of birth). (source)

Psychologists Daniel Simons of the University of Illinois and Daniel Levin of Vanderbilt University performed and experiment wherein a researcher stopped students inside a college campus, pretending to be lost. During these conversations, two accomplices walked between the researcher and the student while carrying a large door, allowing the first researcher to be substituted for one of different appearance. Half of the students didn't notice that they had ended up chatting to a different person, even though they had spoken to the stranger for 10 to 15 seconds. This phenomenon is called "change blindness" by psychologists. (source)

Psychologists Daniel Simons and Christopher Chabris performed an experiment where they asked subjects to watch a video of some people playing basketball and asked them to count the number of passes made by one of the teams. At the end of the video, subjects were asked whether they had noticed anything unusual in the video. About half said no, they noticed nothing unusual, missing a woman dressed in a gorilla suit who walked slowly across the scene for nine seconds, passing between the players and briefly turning towards the camera to thump her chest. When the tape was played to subjects who were not asked to count passes, they all saw the gorilla. (source)

People are much more likely to return a lost wallet they have found if they find a picture of a baby inside.