The passage mainly aims to________.

Scientists have come up with a theory for why time flies when you are having fun. Scans have shown that patterns of activity in the brain change depending on how we focus on a task. (18)Concentrating on time passing, as we usually do when bored, will trigger brain activity which will make it seem as though the clock is ticking more slowly. A research result showed that a network of brain regions was activated when more subjects were paid attention to in the duration. (19) It is thought that if the brain is busy focusing on many aspects of a task, then it has to spread its resources thinly,and pays less heed to time passing. Therefore, time passes without us really noticing it, and seems to go quickly.
    However, if the brain is not stimulated in this way, it concentrates its full energies on monitoring the passing of time. (20)This may make time seem to drag, but in fact it is probably a more accurate perception of reality. Indeed, the researchers found that the more volunteers concentrated on the duration of the images, the more accurate were their estimates of its duration. Lead researcher Dr Jennifer Coull said many of the areas of the brain involved in estimating time were the same that played a key role in controlling movement, and preparing for action.