Painful, emotional memories that people would most like to forget may be the toughest to leave behind, especially when memories are created through visual cues, according to a new study by the University of North Carolina at Chapel Hill.

“When you’re watching the news on television and see footage of wounded soldiers in Iraq or ongoing coverage of national tragedies, it may stick with you more than a newspaper headline,” said the study’s lead author, Keith Payne, an assistant professor of psychology in the College of Arts and Sciences.

It is adaptive to be able to intentionally forget neutral events such as wrong directions, a friend’s outdated phone number or a switched meeting time. Intentional forgetting helps update memory with new information, Payne said.

But Payne and former psychology graduate student Elizabeth Corrigan found that even “mild” emotional events, like getting a bad grade on a test or a negative comment from a coworker, can be hard to forget. Their study, “Emotional constraints on intentional forgetting,” appears in the September 2007 print issue of the Journal of Experimental Social Psychology.

When people are trying to intentionally forget information, they need to mentally segregate that information and then block off the information they don’t want to retrieve, Payne said.

Emotion undermines both of those steps. “You make a lot of connections between emotional events and other parts of your life, so it might be difficult to isolate them. As far as blocking retrieval of an unwanted event, emotion makes events very salient and therefore highly accessible,” Payne said.

Their results contrast with previous studies of emotional events and intentional forgetting, but those studies used emotion-laden words as stimuli, like “death” and “sex.” The UNC study took a new approach, asking 218 participants to react to photographs instead of text.

“The word ‘murder,’ for instance, may or may not make you afraid, but if you see a graphic, violent picture, it may be powerful enough emotionally to change the way you feel,” Payne said.

The researchers found that their subjects could not intentionally forget emotional events as easily as mundane ones. They also found that both pleasant and unpleasant emotional memories were resistant to intentional forgetting.

The UNC findings contribute to understanding the ways that emotion constrains mental control and to the question of whether intentional forgetting can be helpful in coping with painful or traumatic experiences.

“Our findings add to accumulating evidence that emotion places limits on the ability to control the contents of the mind,” Payne said. “Our results suggest that even a relatively mild emotional reaction can undermine intentional forgetting. But this doesn’t necessarily mean that emotional memories can never be intentionally forgotten. If the motivation to forget is powerful enough, individuals might be able to overcome the effects of emotion by enlisting additional coping strategies.”

A different study would be needed to examine what treatment and coping strategies might be effective in helping people voluntarily forget an unwanted memory, he added.