Nobel Prize-winning psychologist Daniel Kahneman and his colleagues have shown that what we remember about the pleasurable quality of our past experiences is almost entirely determined by two things: how the experiences felt when they were at their peak (best or worst), and how they felt when they ended. This "peak-end" rule of Kahneman's is what we use to summarize the experience, and then we rely on that summary later to remind ourselves of how the experience felt. The summaries in turn influence our decisions about whether to have that experience again, and factors such as the proportion of pleasure to displeasure during the course of the experience or how long the experience last, have almost no influence on our memory of it.
Here's an example. Participants in a laboratory study were asked to listen to a pair of very loud, unpleasant noises played through headphones. One noise lasted for eight seconds. The other last sixteen. The first eight seconds of the second noise were identical to the first noise, whereas the second eight seconds, while still loud and unpleasant, were not as loud. Later, the participants were told that they would have to listen to one of the noises again, but that they could choose which one. Clearly the second noise is worse - the unpleasanness lasted twice as long. Nonetheless, the overwhelming majority of people chose the second to be repeated. Why? Because whereas both noises were unpleasant and had the same aversive peak, the second had a less unpleasant end, and so was remembered as less annoying than the first.
Here's another, quite remarkable example of the peak-end rule in operation. Men undergoing diagnostic colonoscopy exams were asked to report how they felt when it was over. Most people find these exams, in which a tube with a tiny camera on the end is inserted up the rectum and then moved around to allow the inspection of the gastrointestinal system, quite unpleasant - so much so that patients avoid getting regular tests, much to their peril. A second group had a standard colonoscopy plus. The "plus" was that after the actual examination was over, the doctor left the instrument in place for a short time. This was still unpleasant, but much less so because the scope wasn't moving. (Note that both groups of patients were having the colonoscopy for legitimate medical reasons; they were not subjecting themselves to these procedures just for the sake of the experiment.) SO the second group experienced the same moment-by-moment discomfort as the first group, with the addition of somewhat lesser discomfort for twenty seconds more. And that is what they reported, moment-by-moment, as they were having the procedure. But a short time after it was over, the second group rated their experience as less unpleasant than did the first. Whereas both groups had the same peak experience, the second group had a milder end experience.
And it made a difference. It turned out that, over a five-year period after this exam, patients in the second group were more likely to comply with calls for follow-up colonoscopies than patients in the first group. Because they remembered their experiences as less unpleasant, they were less inclined to avoid them in the future.
- Excerpted from The Paradox of Choice by Barry Schwartz (p. 49 - 50)