New studies suggest that when people think unpleasant events are over, they remember them as being less painful or annoying than when they expect them to happen again, pointing to the power of expectation to help people brace for the worst.
In a series of eight studies exposing people to annoying noise, subjecting them to tedious computer tasks, or asking them about menstrual pain, participants recalled such events as being significantly more negative if they expected them to happen again soon.
This reaction might be adaptive. People may keep their equilibrium by using memory to steel themselves against future harm, said co-authors Jeff Galak of Carnegie Mellon University, and Tom Meyvis of New York University.
The laboratory studies (of 30, 44, 112, 154, 174, 160 and 51 subjects) exposed people to five seconds of vacuum cleaner noise.
People who were told they would have to listen to more vacuum cleaner noise said it was significantly more irritating than people who were told the noise was over.
Subsequent studies replicated this finding using larger samples and boring, repetitive tasks - such as dragging circles from the left to the right side of a computer screen 50 times.
Again, people who were told they would have to do it again said the task was significantly more irritating, boring and annoying than people told when they were done.
Other studies varied the method to allow researchers to understand what subjects were experiencing emotionally.
For example, the researchers found evidence that people used more intensely negative memories to steel themselves against the future.
Also, not having time to reflect on the first experience, or having their resources drained by a demanding 'filler' task, reduced the power of expectation.
Also, people recalled fun activities, such as playing video games, as equally enjoyable whether they thought they would play again or not.
The authors concluded that emotions negatively shape memory's judgment of unpleasant experiences, but positively shape the recollected quality of pleasant experiences.
In the culminating field study of 180 women (average age 29), those whose menstrual periods had ended fewer than three days earlier or who expected their periods within three days remembered their last period as significantly more painful than women in the middle of their cycle (none were currently menstruating).
"The prospect of repeating an experience can, in fact, change how people remember it," the authors concluded.
The American Psychological Association has published the studies.