Most of us trust that our memories are factual, fair, and accurate. They are none of the above. There are many factual inaccuracies and gaps in people’s memories. (Azar, 1997; Brewin, Andrews & Gotlib, 1993) Our memories are less like a snapshot in time and more like a creative storybook that is constantly being rewritten and tweaked. A variety of factors influence our memory of an event: social pressure, personal prejudice, future events and beliefs, random miscoding (or errors in recollection), the slightest hint or suggestion from another, as well as our own current perspectives and beliefs.
Researchers in one study showed volunteers a series of slides depicting a red car as it cruises towards a yield sign, turns right, and knocks over a pedestrian. Volunteers were then divided up into two groups. One group was asked this question: "Did another car pass the red car while it was stopped at the stop sign?" The other group wasn't asked any questions at all. Both groups were then shown two sets of pictures; one where the car was approaching a stop sign, the other of the car approaching a yield sign. Each person was then asked which was the scene they just saw in the slides. More than 90% of those who weren't asked any questions answered correctly. Of those who were asked that one seemingly innocent question, 80% got it wrong, pointing to the picture of the car approaching the stop sign as opposed to the yield sign - a complete 180 shift in accuracy. (Loftus, Miller & Burns, 1978) The simple act of asking a question about what they saw overwrote their memory of what they actually experienced.
The same is true when we tell another about our experiences. If a person is given an experience and then told to tell someone else about that experience, their brain works in subtle changes to the original memory and they will remember not what they actually experienced, but what they said about what they experienced. (Schooler & Engstler-Schooler, 1990) As social psychologist Daniel Goleman states, "Whenever we retrieve a memory, the brain rewrites it a bit, updating the past according to our present concerns and understanding. ...Thus each time we bring a memory to mind, we adjust it's very chemistry: the next time we retrieve it, that memory will come up as we last modified it." (Goleman 2006 pg 78)
This means that suggestion and social persuasion has a big impact on what we remember to be true. Our memories contain not so much what actually happened to us in the past, but what we and others believe to have been. The frightening part about such research is that the preceding example was nothing more than an innocent question. We are all subjected to far more powerful social influences in our daily lives that distort our recollection to a far greater degree than a single-sentence question. So if a mere question can alter the memory of what someone saw just 5 minutes ago, how much more does it influence our recollection of events when we’re subjected to social persuasion that is far more powerful and which occurs over far greater spans of time?
Memory is also molded by expectation and stereotypes. Many studies have shown that beliefs about gender or other biases will change our emotional memory about events. (Robinson, & Clore, 2002; Robinson, Johnson & Shields, 1998) For example, in one study, women were asked to keep a journal about their lives. When asked to recall how they felt on a particular day at a later time, they remembered being moodier and more emotional during their minstrel cycle. Yet their journal entries showed otherwise. There wasn't any mood difference at all between those days and the rest of the month. Yet that didn't stop their belief in this stereotypical assumption from altering their own memory of how they felt. (McFarland, Ross & DeCourville, 1981)
Memory is also subject to perception; both past and present. Another unfortunate reality is that our memories were never accurate to begin with, because even as we witness or experience an event, the information our brain takes in is being warped according to our beliefs and perspectives. Studies have shown that when an auditorium full of people witness a mock crime, they can all come up with quite different and often contradictory descriptions of exactly what occurred. Though they all witnessed the same event, their brain distorted what they saw, missed some bits of important information, and added other bits even as it was occurring. Our brains take in around 2 billion bits of information per second, yet our minds process only about 2,000 of those bits, or one one-millionth of the information our senses take in. From this sea of information, its are parsed according to what our brain deems important, and it does this on its own below our conscious awareness. That's a lot of room for error, and the information sorted is further dictated by our personal beliefs and expectations; the metaprogram of the mind. It, after all, decides what we notice and what we don't.