Although the actual interruption may only last a few moments, the study shows that we then lose more time when we try to find our place and resume the task that was interrupted.

The research, led by Dr Helen Hodgetts and Professor Dylan Jones at Cardiff University, examined the cost of on-screen interruptions in terms of the time taken to complete a simple seven-step computer task.

The researchers found that, even after only a five second interruption, people take longer than normal to complete the next step in the task they are working on.

"The interruption breaks our cognitive focus on the task in hand, so we have to work out where we were up to and what we were planning to do next before we can resume the task at our original speed" explains Dr Hodgetts.

The interruptions only caused a few seconds delay in resuming the simple task set in the experiments but in a more realistic work environment, where there is more information to retrieve after the interruption, the loss of concentration could have a greater impact on work performance.

"Our findings suggest that even seemingly brief and inconsequential on-screen pop-up messages might be impacting upon our efficiency, particularly given their frequency over the working day," says Dr Hodgetts.

Other results from the study show that an interruption lag - a brief time between a warning for an upcoming interruption and the interruption itself- can reduce the time we lose trying to find our place again

A warning sound was found to be most effective because it allows us to consolidate where we are in the current task before transferring our attention to the interruption. In contrast, a flashing warning signal on the computer screen can be just as disruptive as the interruption itself

The benefits of having time to rehearse our place or lay down mental 'cues' to help us back to where we were in a task (before we divert our attention to deal with an interruption) has practical implications for the design of computer pop-ups.

The researchers suggest that e-mail alerts and similar pop-up messages should be as small and discrete as possible and should not obscure the original activity. Better still, any visual alert should disappear after a few seconds if not responded to, so that we can be aware that there is incoming information without having to interrupt our current task.

The researchers also point out obvious practical steps that computer users can take to minimise unscheduled pop-up notifications, particularly whilst engaging in tasks that require a lot of planning or concentration:

Instant-messenger systems should be turned off or at least set to 'busy' so that colleagues are aware that unimportant interruptions are not welcome; and e-mail alerts could be turned off or only enabled for messages that the sender tags specifically as high priority.