To study the 'return trip effect', as it is called, they asked 20 men to take off their watches and view two films, ten minutes apart.The films were the same length and had been recorded by the Japanese researchers as they walked set routes. Half of the men watched two outward journeys. The others saw a round trip.To measure how quickly the men perceived time to be passing during their ‘journey’, they were asked to speak up every time they thought three minutes of the film had passed.

And after watching both films, they were asked which seemed longer.Those who had watched the round trip thought the second film was shorter.　Curiously, they didn’t feel time pass more quickly while watching the films.

It was only when asked to compare the two films at the end of the experiment that the ‘return trip effect’ kicked in.The University of Kyoto researchers said that simply knowing we are on the homeward leg of a trip may make it seem shorter, when looking back.

Previous studies have attributed to phenomenon to the effects of concentration and anticipation.It is thought that when we are going somewhere, we are focusing on getting there on time and every second counts.In contrast, when we are heading home, the pressure is off, we think of other things, and the journey passes more quickly.

Another explanation is that we are too optimistic when we start to travel, leading to us under-estimating how long the trip will take.As a result, we are unnecessarily negative about how long the return journey will be and so are pleasantly surprised when it goes well.Interestingly, the effect isn’t due to a route being more familiar on the homeward leg.

Research shows that people experience the feeling of time flying even when they return home by a different route. Scientists say that whatever the reason behind the effect, it is something to enjoy.After all, it leaves us feeling good after a long commute and when a holiday ends.

该研究是为了从两方面了解我们对时间的理解——实时和回顾，而实验结果说明我们在这两种情况下对时间的理解有差异。
研究人员发现，两组人在实验中对时间的估计差不多，然而当他们在实验后进行回忆时，观看了往返程录像的人认为返程更短，而另一组人并没有这种体会。研究结果说明返程相应与事后回忆和描述相关，也就是说，只有在知道正在返程的路上时，才会出现“返程效应”。
这种效应出现的具体原因还不清楚，不过心理学家们提出了几种理论。

其中一个认为返程效应与关注时间本身有关。当你更多地关注时间流逝，比如你迟到时不断看手表，时间似乎过得很慢。但当你的注意力放在其他地方，比如一些更有趣的事物上，时间就会过得比较快。这个观点并不新颖，人们经常说“开心的时光总是过得很快”，它也可以解释当生命受到威胁时时间似乎会慢下来的现象。而这对我们的记忆也有影响，如果我们在对一段时间的注意力更集中，记忆中这段时间就会更长。也就是说，对当前的关注实际上会让大脑对时间流逝的理解变慢。

另一个观点认为返程效应与熟悉感有关。在去的过程中，你对路途并不了解，然而在返程中，你会认出一些地标和其他熟悉的场景，这让时间过得更快。对于那些经常经过的地方，比如上下班的路途，人们并不会体验到返程效应。有证据显示，当我们遇到不熟悉的事物时，时间似乎会过得很慢，而例行程序则会很快过去。这也就是为什么随着年龄增长，时间似乎会越来越快，因为我们所经历的新鲜事物越来越少。

不过这可能并不能完全解释返程效应，一些研究人员发现，即使在不熟悉的地方，也可能经历返程效应。2011年的一项研究中，心理学家让一群骑行者骑到一个市场，接着将他们分成两组，一组原路返回，另一组则骑过一段距离相等但并不熟悉的路程，最终两组人都出现了返程效应。

这一研究总结认为人们通常在出发时非常乐观，这让去程显得更长，返程时，他们的期望值会发生变化，希望能更快回去，这却让整个过程感觉更长。研究作者认为，这就是为什么我们在每天上下班时不会体验到返程效应，因为我们对这一路程太熟悉，而对所需时间已经有非常准确的预估。

总而言之，回程效应可能是几种因素的组合，可能有些因素心理学家尚未发现。但目前的研究表明，人类的时间流逝感觉是一种主观体验，或长或短并不准确。