Time Flies When You’re Having Fun: The neuroscience of time perception

It’s easy to look back on your younger years with a melancholic longing, but this feeling often runs deeper than simple childhood nostalgia. It isn’t just our childhood we miss, but how the world felt; the way that time seemed to expand into interminable school terms and never-ending summer holidays. 

It is common for time to feel as if it speeds up as you age. A year at 10 years old can last a lifetime, but a year at 40 years old can feel like the blink of an eye. What changes how our brains perceive the world, causing time to accelerate in this way? 

Prospective versus retrospective time estimation:

Rather than functioning like a mental clock reliably ticking with each passing second, time perception is influenced by many factors, including perception, attention and memory, which change as you gain life experience. 

The predictive processing model of time perception presented by Fountas et al. (2022) states that perceived time is a function of the number of episodic memories from that time period. Episodic memories form our mental diary of past life experiences, detailing events from our personal lives along with their context in terms of time, place, and associated emotions. However, there is a clear distinction between how the frequency of episodic memory affects prospective and retrospective time estimation. 

When judging the length of a time period as it unfolds (prospectively), fewer episodic memories are associated with the experience of time passing more slowly. For example, a day at work may feel as if it lasts longer than it actually does, as there are few distinctive episodic events differentiating it from any other shift. However, when judging time retrospectively, periods containing fewer episodic memories are often perceived as having passed more quickly. Looking back on a week of going to work every day, the repetition and lack of novel memories may make it feel like the week passed you by. 

Retrospectively, episodic memories act as timestamps which lengthen the perceived time. Time on holiday may fly by due to the density of novel experiences to process, but when you get home it may feel like you were away for longer than you were, due to the high frequency of stand-out memories. 

Predictive processing account of time perception: 

The brain constantly updates internal representations of stimuli with new sensory information, creating predictive models of our environment which are used in the future. This process makes perception more efficient, allowing us to accurately predict our visual surroundings when in familiar environments, rather than having to individually process every piece of sensory data. When a stimulus violates these predictive models, the perceptual surprise of an unpredicted sensory event leads to the event being encoded as salient, attention being captured, and the event being recorded into episodic memory. 

Many studies have shown that retrospective time estimation positively correlates with the number of sensory events which are encoded into episodic memory. A classical study by Poynter (1983) manipulated event segmentation to measure the effect on retrospective time estimation. Participants were told to memorise words belonging to a particular category (target words) from a word list read to them from an audio tape. The three relevant target words were placed in position 1, 2, and 3 of the word list (unsegmented condition) or distributed evenly across the list (segmented condition) (Figure 1). As the target words were relevant to the task, it was assumed they would be encoded as salient and encoded into episodic memory; thereby breaking the time period up into distinct event segmentations. 

Figure 1. Diagram of Poynter (1983)'s study set-up. Target words were placed in position 1, 2, and 3 of the word list (unsegmented condition) or distributed evenly across the list (segmented condition). Participants were told to memorise the target words belonging to a particular category from a word list read to them from an audio tape.

Results showed that when asked to estimate the length of the tape, participants’ retrospective time estimates were significantly greater for the segmented condition. The more a time period is parcellated into distinct episodic episodes, the longer its perceived duration afterwards.

Time perception as adults: life in autopilot mode

As adults, we create routines that make our every day relatively similar, meaning that our perceptual systems are often able to predict the sensory world around us. With our perception of the world a neural combination of our internal environmental models and raw sensory input, adult routines make you rely more and more on the former. 

Chan et al. (2021) used an illusion task while recording magnetoencephalography data and found that older adults (aged 58-72) perceived more illusions than younger adults (aged 21-28), indicating an increased reliance on predictive templates of sensory stimuli. Older adults also exhibited illusion-related modulation of connectivity from the auditory cortices to the visual cortices, suggesting that older adults are more likely to use auditory and visual neural templates of reality during perception. 

When our internal models accurately predict our surroundings, the lack of perceptual surprise means that our attention is not captured, and the event is not encoded into episodic memory. This occurs not only for our perception, but also our actions: frequent repetition of procedures leads to automatic processing of learned sequences without attention being engaged. Living in our routine often results in repeated experiences becoming indistinguishable in memory, meaning time passes us by. 

Time perception as children: 

As children, we experienced the world for the first time. The walk to the shops that you have now performed countless times used to be novel; you hadn’t noticed the way the light filtered through the trees before, or that was the first time you ever managed to ride your bike without stabilisers. 

Such novel experiences are not predicted by children’s internal expectations of the world, due to their lack of life experience. Therefore, that attention is captured by surroundings and is required for activities which become automatic by adulthood (e.g., walking or riding a bike). 

This high proportion of novelty results in many events being encoded as salient, meaning time feels long and rich with new information and experiences.

Elongating time as adults:

So how do we get our time back? Obviously, it isn’t possible to erase all your life experience to perceive everything for the first time again, but you can make small changes to your routine to make today more distinguishable from yesterday. For example, take a different route home from work, spend half an hour mindlessly doodling, or start a conversation with someone you wouldn’t normally speak to. These out-of-the-ordinary events would not be predicted by your perceptual system, and therefore are more salient and likely to be encoded into episodic memory. Avni-Babad and Ritov (2003) found that when looking back on a routine task, the duration of the task is perceived as shorter than looking back on a novel task. So, shock your brain out of autopilot mode by surprising it with something new!

Another way to make your day feel longer is to reduce your screen time. Time distortion is a hallmark feature, and one of the addictive aspects, of smartphone use. You can spend 30 minutes scrolling through short-form content like TikTok, and not be able to recall one specific video that you just watched. Such passive viewing, or ‘doomscrolling’, where few salient episodic memories are recorded, results in the time feeling shorter than it was. 

Reducing screen time can even alter your perception of time spent in the real world. Turel and Cavagnaro (2018) found that one week’s abstinence from social media was linked to upward time distortion trends: perceiving the time it took to complete a survey as longer than they perceived the survey to take the week before. 

Conclusion: 

The perception of longer time periods within people’s lives is tricky to study scientifically due to a lack of objectivity, resulting in laboratory studies making inferences about how we might perceive time in the long-term from data about the time perception of short-term tasks. Future research could focus on longitudinal data which could measure how the frequency of episodic memories that participants can recall from a time period relates to the perceived duration of that time period. 

To recap: a time period with few episodic memories may drag in the moment, but will feel disproportionately fast when you look back on it. This position, often a byproduct of living in autopilot in your adult routine, contributes to the feeling that “The days are long, but the years are short”. Individual days drag by as you re-live experiences, but when looking back, the scarcity of breaks from your routine makes time fly by. 

In contrast, a time period with many episodic memories feels fast whilst you are living it, but the density of memories makes it feel longer when looking back on it. Time flies when you are having fun, but expands when you look back on your fun!

References

• Avni-Babad, D., & Ritov, I. (2003). Routine and the perception of time. Journal of Experimental Psychology: General, 132(4), 543. 

• Chan, J. S., Wibral, M., Stawowsky, C., Brandl, M., Helbling, S., Naumer, M. J., ... & Wollstadt, P. (2021). Predictive coding over the lifespan: Increased reliance on perceptual priors in older adults - A magnetoencephalography and dynamic causal modeling study. Frontiers in Aging Neuroscience, 13, 631599.

• Fountas, Z., Sylaidi, A., Nikiforou, K., Seth, A. K., Shanahan, M., & Roseboom, W. (2022). A predictive processing model of episodic memory and time perception. Neural computation, 34(7), 1501-1544.

• Poynter, W. D. (1983). Duration judgment and the segmentation of experience. Memory & Cognition, 11(1), 77-82.

• Turel, O., & R. Cavagnaro, D. (2019). Effect of abstinence from social media on time perception: Differences between low-and at-risk for social media “addiction” groups. Psychiatric Quarterly, 90(1), 217-227.

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This article was written by Amy Marsh and edited by Rebecca Pope, with graphics produced by Saba Keshan. If you enjoyed this article, be the first to be notified about new posts by signing up to become a WiNUK member (top right of this page)! Interested in writing for WiNUK yourself? Contact us through the blog page and the editors will be in touch.