A pat on the back from your boss may be counterproductive, according to a recent study.

One researcher from the University of Greenwich found that receiving praise and recognition in the workplace motivates us for simple tasks but not for more complex projects.

"The rewards that most people experience in relation to their day to day work are not financial, but rather verbal or written recognition from their manager," Dr. Rebecca Hewett, senior lecturer in Human Resources Management with the university's Business School, said in a statement. "However, while managers can use these 'verbal rewards' -- often as simple as saying 'thank you' -- for simple or repetitive tasks, this approach can backfire for complex tasks and projects. That is likely to be because the latter are interesting enough in themselves to be motivating, so that extra encouragement is unwanted. In fact, it can even rob staff of their own inner drive."

For the study, Hewett asked employees to complete a short questionnaire at the end of their working day, each day for two weeks. They answered questions about a specific task that they had spent significant time on that day, and reported their motivation and any rewards that they expected to receive.

They found that individuals reported lower intrinsic motivation if they expected to receive a verbal reward for a complex task -- in other words, they enjoyed the task less, and had a reduced desire to do it. However, study participants' intrinsic motivation was higher when they expected a verbal reward for simple tasks. Researchers believe this is because if the task in itself is not motivating, then the extra encouragement is helpful.

"Often we don't really think about the verbal rewards we use on a day-to-day basis, but actually these are things that are likely to influence people's motivation more than the tangible rewards, which we don't get as frequently," Hewett said. "We all have to do boring tasks in our working day, and this research suggests that managers can help to motivate us to do those simply by providing a bit of encouragement or saying 'thank you'. For those more complex tasks, on the other hand, it would better to let us get on with it."

The findings are detailed in the Journal of Organizational Behavior.