Stagnant relationships kill pleasant memories

"When a couple is considering making a lifelong commitment, they have a lot at stake. It is important that they have accurate recollections of how their relationship evolved," said Brian Ogolsky, professor of Human Development and Family Studies at the University of Illinois in the US.

But, if a couple's relationship is undergoing a slow and painful death, it no longer serves their purpose to remember the course of the romance accurately.

The nine-month study followed 232 never-married heterosexual couples who had dated for just over two years on average.

Each member of the couple reported on their chances of marrying, being careful to take their partner's views into consideration.

Each month, participants rated their chances of marriage from 0 to 100 percent, and researchers plotted a graph from the results.

At the end of the study, participants reflected on their entire relationship to see how their recollections matched up with reality.

"Couples who had deepened their commitment remembered their relationship history almost perfectly," Ogolsky concluded.

The study appeared online in the journal Personal Relationships.