Have you ever gone somewhere and found on the return trip you just couldn't wait to get home? And barring three hours of traffic on the Belt Parkway or a four hour approach to the Tunnels, maybe you actually made it home and thought, "Hey, I got here quicker than I expected! It's great to be home!"
This experience is known as the "return trip effect": People will often feel that the return trip covering the same geographical distance requires less time to complete. It doesn't. When all factors are equalized--same distance, traveling at approximately the same speed, no external delays, roughly the same number of rest stops--the duration of the return trip will be almost identical to the original journey. So why does it feel different? The answer is Time--or rather, our perception of it. A study published by PLOS ONE adds to the growing body of research that shows how our brain processes and interprets matters of Time. 
The return trip effect is not new to science. Let's start with the current hypotheses that help explain this experience:
  • Familiarity: Knowing the path and the difficulties that we might encounter leaves us feeling more prepared. When things happen to disrupt our journey--when unfamiliar stimuli are introduced--we perceive time as moving more slowly.
  • Overestimation: We start most journeys with an optimistic outlook so even minor set-backs can seem like monumental delays. When we start the return trip, we compensate for these delays when we estimate our travel time only to find that we're home faster than we expected to be.
  • Time relevance: When we have an appointment to make, we're more aware of time and more sensitive to delays. This is more often the case on the initial journey when we are headed to a destination. On the return trip home, we may not have the same stringent time requirements, so we may be more relaxed about our observance of time.
While all of these factors contribute to our perception of the passage of time, there's more to the picture. Ryosuke Ozawa and his colleagues had participants take simulated trips by watching 20-minute videos of a person walking to a destination. The videos showed either a round trip experience or a one-way trip. Participants who viewed the one-way trip were shown two videos that highlighted different routes to and from the destination.
Regardless of the video, participants were asked to report when they thought three minutes had passed (without looking at a clock) as they watched the movies. Both groups perceived time as passing at the same rate. However, when participants were asked to reflect on the trip, differences emerged in how they perceived time. The contextual impact of time within a narrative is tied to a specific region of the brain--and it can be fooled.
Our brains track time using different mechanisms. One fires neurons at specific rates and these pulses are tracked over a specific period; this requires an awareness of Time. Instances where time relevance is high force us to pay more attention to the passage of time, and the more attention we pay to time, the longer the passage seems to be. This is known as prospective timing. The other mechanism is based on memory and language processes. For example, asking someone how long a movie was. This requires an estimation that draws on the context of the memory: did you enjoy the movie or have to wait a long time to meet friends prior? This is known as retrospective timing, and can be colored by the overall experience. 
Our relationship to time has a cultural basis, but it's also a personal one. While there are generalities that can guide our perception of the passage of time, we can't escape the narratives that constitute our memories. As these narratives are applied, they reflect our experiences in the larger world, which in turn can impact how we plan for and prepare for subsequent similar events.
Ozawa R, Fujii K, Kouzaki M (2015) The Return Trip Is Felt Longer Only Postdictively: A Psychophysiological Study of the Return Trip Effect. PLoS ONE 10(6): e0127779. doi:10.1371/journal.pone.0127779
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