WHY TIME FLIES WHEN YOU'RE HAVING FUN

"Pleasure and action make the hours seem short," says Iago in Shakespeare's Othello. For coming from the mouth of a villain, this is one of the great truths of life. But are there any biochemical reasons why it should be so?

Theory 1: Retrospective Time Perception or Retrospective Timing (Using Brain's Memory Traces)

Writing in the August issue of the Psychologist, Israeli psychologist Dan Zakay explains why a watched pot never boils, why time flies when you’re having fun.

It has to do, says Zakay, with “one of the most important aspects of psychological time” — our imperfect and biased perception of duration.

We perceive time either retrospectively (by using the brain’s memory traces) or prospectively (by using the brain’s attentional mechanisms), and several factors affect each of these very different processes, explains Zakay.

When awareness of time is not important (when we’re reading a good book or enjoying the company of friends, for example), any time-duration estimation of the activity will be retrospective, Zakay says. Research has also shown that the length of our retrospective estimates of time intervals tend to rely on how much information we processed during the interval. The more information we processed (the greater the attentional demands of the experience), the longer we judge the amount of time that passed.

Imagine you try to recall how long a film was, or how much time it took you to type a report. In such cases the interval itself doesn’t exist any more; what is left of it are only memory traces. The outcome is ‘retrospective duration’.

The main model that explains retrospective timing is called the ‘contextual change model’. The idea is that our cognitive system is trying to retrieve from memory all the data we stored there during the target-interval whose duration we are trying to estimate. Retrospective estimation of a past event’s duration is based on the naive assumption that the more data that was stored in memory during an interval, the longer that interval should be. Thus, retrospective estimation of duration assigns longer durations for intervals when the amount of retrieved information is high, than for intervals for whom the amount of respectively retrieved information is low.

The problem is that in reality, during identical clock-time intervals, more or less information can be stored in memory depending on factors other than actual duration itself. One factor is the intensity of information processing in which one is engaged. For example, when one is asked to solve difficult arithmetic problems such as complex multiplication, more data will be stored in memory as compared with a same clock-time interval during which one is asked to perform simple addition problems. The result will be that the retrospective ‘multiplication interval’ will be estimated to be longer than the ‘addition interval’. In a classic study, Ornstein (1975), presented participants with either a simple or a very complex figure (a circle or an irregular polygon, respectively) and asked them to memorise them. Later on the participants were asked to retrospectively estimate the exposure duration of each figure. Though exposure was identical in terms of clock-time, those participants who were exposed to the simple figure estimated exposure duration to be significantly shorter when compared to participants exposed to complex figures:?much less information needed to be stored in memory.

A second factor is the amount of contextual changes occurring during the interval. The reason is that contextual changes (e.g. changes in background noise or level of lighting in room) are encoded and stored in memory alongside any other task-related information. While trying to make a retrospective estimation of duration, contextual changes are retrieved together with other information types, thus compounding the overall amount of retrieved information. Block and Read’s (1978) experiment involved participants engaging in identical information-processing tasks for a fixed interval. Some participants were exposed to changes in room lighting, the other participants were not exposed to any contextual changes. Consequently, the group exposed to change estimated the duration of the target interval as significantly longer than those not exposed.

A third factor refers to the level of segmentation into meaningful sub-intervals. The more an interval is segmented, the longer its retrospective duration estimation will be (Poynter, 1983). Intervals are segmented by high-priority events (HPEs), which attract attention, are stored in memory and are easily retrieved later on. Such HPEs act as cues, facilitating the retrieval of information from memory, thus enabling the retrieval of a larger amount of information leading to longer retrospective duration estimations. Contextual changes are most probably acting as HPEs.

Indeed, Block and Read (1978) suggested that changes in the type of information that should be processed, the context or the mood one experiences during an interval have a high probability of being retrieved, and they concluded that retrospective duration judgement is actually based on the amount of changes of any sort that occurred during the target interval. This is an interesting conclusion because it suggests that the notion of retrospective time is very similar to the notion of physical time: they both reflect change, which might be mental or physical, respectively. The ‘Filled-Time Illusion’ (Wearden et al., 2007), which refers to the common experience that in retrospect intervals filled with intensive mental activity are recalled as longer than same clock-time intervals that were 'empty' of mental activity.

When you recall the duration of a past experience you must rely on your memory of the event – “retrospective timing”. The main psychological model that explains retrospective timing is the “contextual change model”. You estimate the duration of the event by recalling the data stored in your memory of the event. The more data stored, the longer the estimation of the duration of the event.

However, different amounts of information can be stored in memory during identical clock-time intervals, depending on several factors, eg the intensity of the information processing in which one is engaged. The higher the intensity, the longer the duration seems to be. In a classic experiment, participants were asked to memorise either a simple [a circle] or complex figure . Although the clock-time allocated to each task was identical, participants later estimated the duration of memorising the complex shape to be significantly longer than for the simple shape.

Other factors that lengthen retrospective timing estimations are the amount of contextual changes that occur during the interval, or the level of interval segmentation into sub-intervals. These are interpreted by the contextual change model simply as adding to the amount of information stored in memory.

Theory 2: Dopamine

The dopamine clock hypothesis holds that increased dopamine release speeds up an animal’s subjective sense of time—its internal clock. For example, rats treated with amphetamine, which enhances dopamine release, respond earlier than when they are tested without the drug. Curiously, a simple prediction of the dopamine clock hypothesis would seem to be that time doesn’t fly, but rather crawls, when you’re having fun. Unexpectedly pleasurable events boost dopamine release, which should cause your internal clock to run faster. Your subjective sense of time in that case grows faster than time itself, so that short intervals seem longer than they are. The dopamine clock hypothesis accounts for this counterintuitive prediction by an additional assumption about attention: When things are good, attention to time is reduced, such that intervals seem shorter than they are (5).

To clarify the role of dopamine in interval timing, Soares et al. investigated midbrain dopamine neuron activity in the substantia nigra pars compacta (SNc) of mice performing a timing task. They presented mice with two brief tones, and trained them to classify the interval between the tones as shorter or longer than a standard criterion. They then observed calcium influx into dopaminergic SNc neurons, which signals activity. Consistent with standard reinforcement learning theory, the authors observed bursts of activity in dopamine-synthesizing neurons that were locked to the second tone, reflecting the probability of an upcoming reward. This probability was greatest when the in-tertone duration was much shorter or much longer than the criterion—i.e., when the duration could be easily discriminated from the intermediate, criterion duration.

Again, in rodents, Paton and his colleagues found that a set of neurons that releases the neurotransmitter dopamine — an important chemical involved in feeling rewarded — impacts how the brain perceives time. When you're having fun, these cells are more active, they release a lot of dopamine and your brain judges that less time has passed than actually has. When you're not having fun, these cells don't release as much dopamine, and time seems to slow down.

Paton and his colleagues found that a set of neurons that release the neurotransmitter dopamine — an important chemical involved in feeling rewarded — impacts how the brain perceives time. When you're having fun, these cells are more active, they release a lot of dopamine and your brain judges that less time has passed than actually has. When you're not having fun, these cells don't release as much dopamine, and time seems to slow down.