Scientists have used an unconventional technique to increase the happiness of married couples: brain washing them with pictures of cute puppies.

The team developed a procedure that could be used as part of marriage counselling to improve people's feelings about their partners. The intervention could be used to keep the spark alive in long-distance and challenging relationship situations, such as those experienced by members of the armed forces.

Keeping a marriage healthy and happy is a challenging task – there's even a mathematical formula to keep the love alive. Happiness is a really important metric and previous research has shown that if happiness level of males is higher than their partner it's more likely to end in divorce.

The team of psychologists wanted to find out whether it was possible to improve marital satisfaction by subtly brain washing the study participants, a process called evaluative conditioning. They designed an experiment to retrain the automatic responses of married people when they think about their partner.

"One ultimate source of our feelings about our relationships can be reduced to how we associate our partners with positive affect, and those associations can come from our partners but also from unrelated things, like puppies and bunnies," said James K McNulty, lead researcher from Florida State University.

The study included 144 married couples who were all under 40 and married for less than 5 years. At the start of the experiment, couples completed a series of tests to measure their relationship satisfaction.

This included measuring their immediate, automatic attitudes toward their partner. Like a scary word association game that could lead to divorce.

To improve the automatic reactions to their spouse subjects were asked to watch a short, happy montage of images once every three days for six weeks.

For those in the experimental group, they were shown pictures of their spouse alongside positive stimuli, such as a puppy that makes you grit your teeth and die from happiness, or the word "wonderful". In the control group, the participants saw their partner's face with pictures of neutral stimuli such as a shirt button.

Did the positive stimuli actually make them perceive their partner in a more positive light?

To test the effect that the montage was having on the couple, every 2 weeks for 8 weeks each spouse was shown a series of faces, including their partners and were asked to indicate the emotional tone of the image as quickly as possible.

Something amazing happened to the participants.

The simple act of associating their partners with positive stimuli increased the marital satisfaction over the course of the study.

"I was actually a little surprised that it worked," McNulty explained. "All the theory I reviewed on evaluative conditioning suggested it should, but existing theories of relationships, and just the idea that something so simple and unrelated to marriage could affect how people feel about their marriage, made me skeptical."

Of course, the research only measured one aspect of relationship happiness and the researchers were quick to point out that behaviour also plays a big part in determining happiness.

Although this simple intervention focused on automatic attitudes, the researchers say it could be useful as one aspect of marriage counselling.

"The research was actually prompted by a grant from the Department of Defence – I was asked to conceptualise and test a brief way to help married couples cope with the stress of separation and deployment," McNulty said. "We would really like to develop a procedure that could help soldiers and other people in situations that are challenging for relationships."

As long as researchers keep coming up with more reasons to look at pictures of cute puppies we're not going to complain.

The research was reported in Psychological Science.