The decision to opt for a chocolate snack over an apple is not a simple matter of taste, according to research by Anirban Mukhopadhyay and his co-author Aparna A. Labroo. Rather, the person will be guided by a complex interplay of mood and their beliefs about whether emotion is lasting or fleeting.

"Some of life's most fundamental choices involve balancing immediate feelings and long-term interests," they said. "We argue that people's inference about whether their mood, either positive or negative, will improve if left to itself, determines whether or not they engage in activities to improve their mood."

"People who feel good rather than bad will be more likely to indulge if they believe their emotion is fleeting because they infer that unless they take actions to feel better, the positive feelings will pass. Whereas people who feel bad in this situation will infer their actions to feel better are unnecessary because the negative feelings will pass on their own."

"In contrast, if people believe emotion is lasting, those who feel bad will be more likely to indulge because they infer that unless they act to feel better, the negative feelings will persist, but people who feel good infer they can act in their long-term interests because actions to preserve their mood are unnecessary."

The authors confirmed these ideas in six experiments that manipulated and measured mood and people's views on the transience of emotion, then asked them to make a choice.

Repeatedly, participants indulged either when they were happy and believed emotion was fleeting (to preserve their mood), or when they were unhappy and thought emotion was lasting (to change their mood). Otherwise, they showed restraint and acted in their long-term interests.

In one experiment, participants were asked to choose between chocolate and an apple after coloring a line drawing of either a happy or a sad face. They had also replied to questions about their views on emotional transience and those who thought emotion was fleeting and were exposed to the happy face had a much higher preference for chocolate than those exposed to the sad face (60 per cent against 25 per cent). But if they thought emotion was lasting, the happy face group were less likely to indulge (27 per cent against 60 per cent of sad face participants).

As the authors summarised: "They acted in their long term interests and chose a healthy apple unless they inferred a need to regulate their affect."

Happy moods can also be linked to avoidance. Other research has shown happy people who want to regulate their immediate mood were less willing to donate to a charity concerning child deaths from defective products, unless they were prompted to consider the long-term benefits of becoming a better person by helping others. The authors used this material in separate experiments that primed participants' moods and views on emotion transience, then invited them to read about the charity if they wished. They were also asked whether they would make a donation.

Those with a happy prime who believed emotion was fleeting spent about half as much time looking at the materials as did those who had an unhappy prime. They also donated less than half as much money. But when they thought emotion was lasting, they spent significantly longer than the unhappy group with the materials and donated about eight times as much money.

Similar results were found in the rest of the experiments, although one showed that when people were made aware of their mood and emotional transience theories, they corrected for them and there was no significant impact on whether they indulged or not. "When people are made aware of these theories, they recognise their tendency to over-generalise and also recognise the theories as sources of influence that seem irrelevant to their judgement. Thus they try to avoid being influenced," the authors said.

In summary, "We argue that people act in their long-term interests unless they infer a need to immediately improve their current mood. We also introduce a new construct apart from mood that pertains to lay beliefs about the transience of emotions, and show how both of these factors systematically influence affect regulation," they said.