A mobile phone app that plays quiet soundscapes while people sleep could make their dreams more pleasing, a British psychologist claims.

A study of 800 people found that those who listened to sounds of nature shortly before they woke had more positive dreams than those who listened to sounds of the city.

The findings come from a mass experiment launched in 2010 at the Edinburgh Science Festival to investigate whether it is possible to use sounds to steer people's dreams.

Richard Wiseman, who led the experiment at the University of Hertfordshire, said the technology could help people start the day in a better mood.

That may be some time off though. The effect on the emotional tone of dreams was small, and the study did not record whether people actually felt happier or more positive when they woke up.

Participants downloaded a free iPhone app called Dream:ON and two soundscapes. The city soundscape played the sounds of traffic, bustling crowds and the occasional faint car horn. The nature soundscape was more tranquil, and played sounds of the wind blowing in trees and birds chirping. The designers avoided sounds of waterfalls and trickling rivers for fear of inducing urination.

Before they went to bed, people chose the soundscape they wanted to hear, and the time they wanted to wake up. A few minutes before the alarm sounded, the app played the soundscape quietly enough not to waken them. As a control, sometimes the app stayed silent, so the effect of the actual sounds could be teased out.

The participants submitted details of their dreams, which researchers rated on content, emotional tone, and how bizarre they were. The reported content was rated for nature and city references on a scale of one to seven. A dream about climbing a tree in a forest would score highly on the nature scale, for example, while a dream about driving a lorry through Manhattan would score highly on the city scale.

Wiseman said that people who listened to the nature soundscape reported more nature-related dreams and vice-versa for the city soundscape. But that may have had nothing to do with the soundscape. People chose for themselves which soundscape they wanted to play, and so knew what to expect.

Also, those who chose the nature soundscape might simply like nature more and be more likely to dream about it. "Participants may just have reported what they expected to dream of," said Mark Blagrove, who studies sleep and dreaming at Swansea University.

Wiseman concedes the weakness, but is more confident that the nature soundscape made people's dreams more positive.

"I think what we are influencing is the emotional tone of people's dreams. In terms of the content, I think that is heavily driven by people's expectations," Wiseman said.

Wiseman has not published the work in a scientific journal, but timed the release of his results to concide with the publication of his book on sleep and dreaming, Night School. Wiseman said that the app and soundscapes used in the study were free for participants to download, but that he got a percentage of sales of other dreamscapes sold for the app. All of the soundscapes will be free from this week, he added.

Previous work has shown that good dreams can improve a person's mood in the morning, and this is where Wiseman thinks the technology might have value. "Hopefully they wake up in a better mood, and it might help them work through their problems," he said.

The study also found that participants reported more bizarre dreams near the full moon. There is some evidence that people have more disrupted sleep around the full moon, which may be a factor.

Josie Malinowski, who studies sleep and dreaming at the University of Bedfordshire, said the study was interesting. "We need better tools to research dreams outside of the lab, so I really welcome this kind of development," she said.

But she added: "It's definitely not the case that the results indicate the app can help people create a perfect dream."