Jonah Lehrer explains how friends ruin memory:
The power of this phenomenon was demonstrated in a new Science paper by Micah Edelson, Tali Sharot, Raymond Dolan and Yadin Dudai. The neuroscientists were interested in how the opinion of other people can alter our personal memories, even over a relatively short period of time. The experiment itself was straightforward. A few dozen people watched an eyewitness style documentary about a police arrest in groups of five. Three days later, the subjects returned to the lab and completed a memory test about the documentary. Four days after that, they were brought back once again and asked a variety of questions about the short movie while inside a brain scanner.
This time, though, the subjects were given a “lifeline”: they were shown the answers given by other people in their film-viewing group. Unbeknownst to the subjects, the lifeline was actually composed of false answers to the very questions that the subjects had previously answered correctly and confidently. Remarkably, this false feedback altered the responses of the participants, leading nearly 70 percent to conform to the group and give an incorrect answer. They had revised their stories in light of the social pressure.
The question, of course, is whether their memory of the film had actually undergone a change. (Previous studies have demonstrated that people will knowingly give a false answer just to conform to the group. We’re such wimps.) To find out, the researchers invited the subjects back to the lab one last time to take the memory test, telling them that the answers they had previously been given were not those of their fellow film watchers, but randomly generated by a computer. Some of the responses reverted back to the original, but more than 40 percent remained erroneous, implying that the subjects were relying on false memories implanted by the earlier session.