Every individual perceives the flow of time differently
Time perception refers to a person’s subjective experience of the passage of time, or the perceived duration of events, which can differ significantly between different individuals and/or in different circumstances. Although physical time appears to be more or less objective, psychological time is subjective and potentially malleable, exemplified by common phrases like “time flies when you are having fun” and “a watched pot never boils”. This malleability is made particularly apparent by the various temporal illusions we experience.
As a field of study within psychology and neuroscience, time perception came of age in the late 19th Century with the studies of the relationship between perceived and measured time by one of the founders of modern experimental psychology, Gustav Theodor Fechner.
We do not so much perceive time itself, but changes in or the passage of time, or what might be described as “events in time”. In particular, we are aware of the temporal relations between events, and we perceive events as being either simultaneous or successive. We also have a perception of the sequence or order of these events.
Our sense of time seems to have originated as a product of human evolution, and it is not a purely automatic or innate process, but a complex activity that we develop and actively learn as we grow. Humans are, as far as we know, the only animals to be consciously aware of the passage of time and our own impermanence and mortality, and to have a consciousness of the past that is anything more than pure instinct and behavioural conditioning.
How We Perceive Time
Although psychologists believe that there is a neurological system governing the perception of time, it appears not to be associated with specific sensory pathways, but rather uses a highly distributed system in the brain (see the section on Biopsychology). Time perception therefore differs from our other senses – sight, hearing, taste, smell, touch, even proprioception – since time cannot be directly perceived, and so must be “reconstructed” in some way by the brain.
Neurotransmitters such as dopamine and norepinephrine (adrenaline) are integrally involved in our perception of time, although the exact mechanism is still not well understood. The human brain appears to possess some kind of “internal clock” (distinct from the biological or circadian clock) which is linked to specific dopamine levels, or possibly even several different clocks working together but independently, each of which may dictate our time perception depending on the particular context (see the section on Biopsychology for more detail).
When the brain receives new information from the outside world, the raw data does not necessarily arrive in the order needed to process it properly. The brain therefore reorganizes the information and presents it in a more easily understandable form. In the case of familiar information, very little time is needed for this process, but new information requires more processing and this extra processing tends to makes time feel elongated. This is part of the reason why a child’s summer seems to last forever, while an old person’s well-practiced routine seems to slip away faster and faster. The more familiar the task, the less new information the brain needs to process, and the more quickly time seems to pass.
To some extent also, the perception of time is associated with other cognitive processes such as attention. Measuring the duration of an event – whether it be the length of time to leave a sauce to simmer, estimating how fast to run to catch a ball, or calculating whether there is enough time to drive through a yellow light – requires a certain amount of attention, and new events appear to take longer than familiar events because more attention is paid to them. For instance, in psychological tests, if the same picture is shown again and again, interspersed every so often with a different picture, the different picture is perceived by the observer as staying on-screen for longer, even if all the pictures actually appear for the same length of time. The difference arises from the degree of attention paid to the pictures.
The perception of time durations is also crucially bound up with memory. It is essentially our memory of an event (and perhaps, even more specifically, our memory of the beginning and end of the event) that allows us to form a perception of, or a belief in, its duration. We infer, albeit subconsciously, the duration of an event from our memory of how far in the past something occurred, of how long ago the beginning and end of the event occurred. It is not clear whether this is done by some measure of the strength of a memory trace that persists over time (the strength model of time memory), or by an inference based on associations between the event and other events whose date or time is known (the inference model).
There is increasing evidence that an animal’s metabolic rate affects the way it perceives time. In general, larger animals have a slower metabolic rate, and time passes relatively rapidly for them. Smaller animals, conversely, tend to have faster metabolisms, and experience time as passing relatively slowly, so that they can perceive more events in the same period. Studies have shown that small animals can in fact distinguish very short and very quick-changing events, which is one reason why a fly can avoid a swatter with such apparent ease. In evolutionary terms, the ability to perceive time on very small scales may be the difference between life and death for small, vulnerable animals.
Sequence and Duration
We perceive time as series of events in a sequence, separate by durations of various lengths. Our experience is not limited to a single series of events, though, but we experience a plurality of overlapping events, sequences and durations.
A metronome ticking at a rate of two or three times a second is perceived as an integral sequence, as a rhythm. When the ticks are less frequent, though, say at intervals of three seconds, the sounds appears to be no longer perceived as a sequence in the same way, and each sound impulse remains an isolated perceptual event. Similar results occur with slowed down speech or music: music or spoken sentences are only recognizable as such when their rhythmic patterns and phrases are presented at an optimal speed that allow them to be recognized as a perceptual unity.
The perception of a duration requires a minimum of about 0.1 seconds in the case of visual stimuli such as a flash, or much less (0.01 to 0.02 seconds) in the case of auditory stimuli. Stimuli of any shorter time than these are therefore perceived as instantaneous, and as not representing any duration at all.