A contemporary quartz watch
Time perception is a field of study within psychology, cognitive linguistics and neuroscience that refers to the subjective experience of time, which is measured by someone’s own perception of the duration of the indefinite and unfolding of events. The perceived time interval between two successive events is referred to as perceived duration. Another person’s perception of time cannot be directly experienced or understood, but it can be objectively studied and inferred through a number of scientific experiments. Time perception is a construction of the brain that is manipulable and distortable under certain circumstances. These temporal illusions help to expose the underlying neural mechanisms of time perception.
Pioneering work, emphasizing species-specific differences, was conducted by Karl Ernst von Baer. Experimental work began under the influence of the psycho-physical notions of Gustav Theodor Fechner with studies of the relationship between perceived and measured time.
William J. Friedman (1993) also contrasted two theories for a sense of time:
- The strength model of time memory. This posits a memory trace that persists over time, by which one might judge the age of a memory (and therefore how long ago the event remembered occurred) from the strength of the trace. This conflicts with the fact that memories of recent events may fade more quickly than more distant memories.
- The inference model suggests the time of an event is inferred from information about relations between the event in question and other events whose date or time is known.
Another theory involves the brain’s subconscious tallying of “pulses” during a specific interval, forming a biological stopwatch. This theory alleges that the brain can run multiple biological stopwatches at one time depending on the type of task one is involved in. The location of these pulses and what these pulses actually consist of is unclear. This model is only a metaphor and does not stand up in terms of brain physiology or anatomy.
The specious present is the time duration wherein a state of consciousness is experienced as being in the present. The term was first introduced by the philosopher E. R. Clay in 1882 (E. Robert Kelly), and was further developed by William James. James defined the specious present to be “the prototype of all conceived times… the short duration of which we are immediately and incessantly sensible”. In “Scientific Thought” (1930), C. D. Broad further elaborated on the concept of the specious present, and considered that the specious present may be considered as the temporal equivalent of a sensory datum. A version of the concept was used by Edmund Husserl in his works and discussed further by Francisco Varela based on the writings of Husserl, Heidegger, and Merleau-Ponty.
Although the perception of time is not associated with a specific sensory system, psychologists and neuroscientists suggest that humans do have a system, or several complementary systems, governing the perception of time. Time perception is handled by a highly distributed system involving the cerebral cortex, cerebellum and basal ganglia. One particular component, the suprachiasmatic nucleus, is responsible for the circadian (or daily) rhythm, while other cell clusters appear to be capable of shorter-range (ultradian) timekeeping. There is some evidence that very short (millisecond) durations are processed by dedicated neurons in early sensory parts of the brain.
Professor Warren Meck devised a physiological model for measuring the passage of time. He found the representation of time to be generated by the oscillatory activity of cells in the upper cortex. The frequency of these cells’ activity is detected by cells in the dorsal striatum at the base of the forebrain. His model separated explicit timing and implicit timing. Explicit timing is used in estimating the duration of a stimulus. Implicit timing is used to gauge the amount of time separating one from an impending event that is expected to occur in the near future. These two estimations of time do not involve the same neuroanatomical areas. For example, implicit timing often occurs to achieve a motor task, involving the cerebellum, left parietal cortex, and left premotor cortex. Explicit timing often involves the supplementary motor area and the right prefrontal cortex.
Two visual stimuli, inside someone’s field of view, can be successfully regarded as simultaneous down to five milliseconds.
In the popular essay “Brain Time”, by David Eagleman, he explains that different types of sensory information (auditory, tactile, visual, etc.) are processed at different speeds by different neural architectures. The brain must learn how to overcome these speed disparities if it is to create a temporally unified representation of the external world: “if the visual brain wants to get events correct timewise, it may have only one choice: wait for the slowest information to arrive. To accomplish this, it must wait about a tenth of a second. In the early days of television broadcasting, engineers worried about the problem of keeping audio and video signals synchronized. Then they accidentally discovered that they had around a hundred milliseconds of slop: As long as the signals arrived within this window, viewers’ brains would automatically resynchronize the signals”. He goes on to say that “This brief waiting period allows the visual system to discount the various delays imposed by the early stages; however, it has the disadvantage of pushing perception into the past. There is a distinct survival advantage to operating as close to the present as possible; an animal does not want to live too far in the past. Therefore, the tenth-of- a-second window may be the smallest delay that allows higher areas of the brain to account for the delays created in the first stages of the system while still operating near the border of the present. This window of delay means that awareness is postdictive, incorporating data from a window of time after an event and delivering a retrospective interpretation of what happened.”
Experiments have shown that rats can successfully estimate a time interval of approximately 40 seconds, despite having their cortex entirely removed. This suggests that time estimation may be a low level process.
Types of temporal illusions
A temporal illusion is a distortion in the perception of time, which occurs when the time interval between two or more events is very narrow (typically less than a second). In such cases, a person may momentarily perceive time as slowing down, stopping, speeding up, or running backwards. Additionally, a person may misperceive the temporal order of these events.
Short list of types of temporal illusions:
- Telescoping effect: People tend to recall recent events as occurring further back in time than they actually did (backward telescoping) and distant events as occurring more recently than they actually did (forward telescoping).
- Vierordt’s law: Shorter intervals tend to be overestimated while longer intervals tend to be underestimated
- Time intervals associated with more changes may be perceived as longer than intervals with fewer changes
- Perceived temporal length of a given task may shorten with greater motivation
- Perceived temporal length of a given task may stretch when broken up or interrupted
- Auditory stimuli may appear to last longer than visual stimuli
- Time durations may appear longer with greater stimulus intensity (e.g., auditory loudness or pitch)
- Simultaneity judgments can be manipulated by repeated exposure to non-simultaneous stimuli
The Kappa effect or perceptual time dilation is a form of temporal illusion verifiable by experiment, wherein the temporal duration between a sequence of consecutive stimuli is thought to be relatively longer or shorter than its actual elapsed time, due to the spatial/auditory/tactile separation between each consecutive stimuli. The kappa effect can be displayed when considering a journey made in two parts that take an equal amount of time. Between these two parts, the journey that covers more distance may appear to take longer than the journey covering less distance, even though they take an equal amount of time.
Chronostasis is a type of temporal illusion in which the first impression following the introduction of a new event or task demand to the brain appears to be extended in time. For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade (e.g., quick eye movement). This elicits an overestimation in the temporal duration for which that target stimulus (i.e., postsaccadic stimulus) was perceived. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception. The most well-known version of this illusion is known as the stopped-clock illusion, wherein a subject’s first impression of the second-hand movement of an analog clock, subsequent to one’s directed attention (i.e., saccade) to the clock, is the perception of a slower-than-normal second-hand movement rate (the seconds hand of the clock may seemingly temporarily freeze in place after initially looking at it).
The occurrence of chronostasis extends beyond the visual domain into the auditory and tactile domains. In the auditory domain, chronostasis and duration overestimation occur when observing auditory stimuli. One common example is a frequent occurrence when making telephone calls. If, while listening to the phone’s dial tone, research subjects move the phone from one ear to the other, the length of time between rings appears longer. In the tactile domain, chronostasis has persisted in research subjects as they reach for and grasp objects. After grasping a new object, subjects overestimate the time in which their hand has been in contact with this object. In other experiments, subjects turning a light on with a button were conditioned to experience the light before the button press.
The perception of the duration of an event seems to be modulated by our recent experiences. Humans typically overestimate the perceived duration of the initial event in a stream of identical events and unexpected “oddball” stimuli seem to be perceived as longer in duration, relative to expected or frequently presented “standard” stimuli.
The oddball effect may serve an evolutionarily adapted “alerting” function and is consistent with reports of time slowing down in threatening situations. The effect seems to be strongest for images that are expanding in size on the retina, in other words, that are “looming” or approaching the viewer, and the effect can be eradicated for oddballs that are contracting or perceived to be receding from the viewer. The effect is also reduced or reversed with a static oddball presented amongst a stream of expanding stimuli.
Initial studies suggested that this oddball-induced “subjective time dilation” expanded the perceived duration of oddball stimuli by 30–50% but subsequent research has reported more modest expansion of around 10%. or less. The direction of the effect, whether the viewer perceives an increase or a decrease in duration, also seems to be dependent upon the stimulus used.
Effects of emotional states
Research has suggested the feeling of awe has the ability to expand one’s perceptions of time availability. Awe can be characterized as an experience of immense perceptual vastness that coincides with an increase in focus. Consequently, it is conceivable that one’s temporal perception would slow down when experiencing awe.
Another temporal illusion, possibly related to the oddball effect, occurs when a person perceives a potential threat or mate (See Fight-or-flight response). For example, research suggests that time seems to slow down when a person skydives or bungee jumps, or when a person suddenly and unexpectedly senses the presence of a potential predator or mate. This reported slowing in temporal perception may have been evolutionarily advantageous because it may have enhanced our ability to intelligibly make quick decisions in moments that were of critical importance to our survival. However, even though observers commonly report that time seems to have moved in slow motion during these events, it is unclear whether this is a function of increased time resolution during the event, or instead an illusion created by the remembering of an emotionally salient event.
Research suggests that the effect appears only at the point of retrospective assessment, rather than occurring simultaneously with events as they happened. Perceptual abilities were tested during a frightening experience – a free-fall – by measuring people’s sensitivity to flickering stimuli. The results showed that the subjects’ temporal resolution was not improved as the frightening event was occurring.
Events appear to have taken longer only in retrospect, possibly because memories were being more densely packed during the frightening situation.
People shown extracts from films known to induce fear often overestimated the elapsed time of a subsequently presented visual stimulus, whereas people shown clips known to evoke feelings of sadness or emotionally-neutral clips from weather forecasts and stock market updates showed no difference. It is argued that fear prompts a state of arousal in the amygdala, which increases the rate of a hypothesised “internal clock.” This could be the result of an evolved defensive mechanism triggered by a threatening situation.
When exposed to a threat, three-year-old children were observed to exhibit a similar tendency to overestimate elapsed time.
The perception of another persons’ emotions can also change our sense of time. The theory of embodied mind (or cognition), as caused by mirror neurons, helps explain how the perception of other people’s emotions have the ability to change one’s own sense of time. Embodied cognition hinges on an internal process that mimics or simulates another’s emotional state. For example, if person #1 spends time with person #2 who speaks and walks incredibly slowly, person #1’s internal clock may slow down.
Depression may increase one’s ability to perceive time accurately. One study assessed this concept by asking subjects to estimate the amount of time that passed during intervals ranging from 3 seconds to 65 seconds. Results indicated that depressed subjects more accurately estimated the amount of time that had passed than non-depressed patients; non-depressed subjects overestimated the passing of time. This difference was hypothesized to be because depressed subjects focused less on external factors that may skew their judgement of time. The authors termed this hypothesized phenomenon “depressive realism.”
Changes with age
Psychologists have found that the subjective perception of the passing of time tends to speed up with increasing age in humans. This often causes people to increasingly underestimate a given interval of time as they age. This fact can likely be attributed to a variety of age-related changes in the aging brain, such as the lowering in dopaminergic levels with older age; however, the details are still being debated. In an experimental study involving a group of subjects aged between 19 and 24 and a group between 60 and 80, the participants’ abilities to estimate 3 minutes of time were compared. The study found that an average of 3 minutes and 3 seconds passed when participants in the younger group estimated that 3 minutes had passed, whereas the older group’s estimate for when 3 minutes had passed came after an average of 3 minutes and 40 seconds.
Very young children literally “live in time” before gaining an awareness of its passing. A child will first experience the passing of time when he or she can subjectively perceive and reflect on the unfolding of a collection of events. A child’s awareness of time develops during childhood when the child’s attention and short-term memory capacities form—this developmental process is thought to be dependent on the slow maturation of the prefrontal cortex and hippocampus.
One day to an 11-year-old would be approximately 1/4,000 of their life, while one day to a 55-year-old would be approximately 1/20,000 of their life. This helps to explain why a random, ordinary day may therefore appear longer for a young child than an adult. The short-term time appears to go faster by square root of their age. So a year experienced by a 55-year-old would pass approximately 2¼ times more quickly than a year experienced by an 11-year-old. If long-term time perception is based solely on the proportionality of a person’s age, then the following four periods in life would appear to be quantitatively equal: age 5 to 10 (1x), age 10 to 20 (2x), age 20 to 40 (4x), age 40 to 80 (8x).
The common explanation is that most external and internal experiences are new for young children, while most experiences are repetitive for adults. Children have to be extremely engaged (i.e. dedicate many neural resources or significant brain power) in the present moment because they must constantly reconfigure their mental models of the world to assimilate it, and properly behave from within. On the contrary, adults may rarely step outside of their mental habits and external routines. When an adult frequently experiences the same stimuli, their brain renders them “invisible” because the brain has already sufficiently and effectively mapped those stimuli. This phenomenon is known as neural adaptation. Thus, the brain will record fewer densely rich memories during these frequent periods of disengagement from the present moment. Consequently, the subjective perception is often that time passes by at a faster rate with age.
Effects of drugs
Psychoactive drugs can alter the judgement of time. These include traditional psychedelics such as LSD, psilocybin, and mescaline as well as the dissociative class of psychedelics such as PCP, ketamine and dextromethorphan. At higher doses time may appear to slow down, speed up or seem out of sequence. In a 2007 study, psilocybin was found to significantly impair the ability to reproduce interval durations longer than 2.5 seconds, significantly impair synchronizing motor actions (taps on a computer keyboard) to regularly occurring tones, and impair the ability to keep tempo when asked to tap on a key at a self-paced but consistent interval. In 1955, British MP Christopher Mayhew took mescaline hydrochloride in an experiment under the guidance of his friend, Dr Humphry Osmond. On the BBC documentary The Beyond Within, he described that half a dozen times during the experiment, he had “a period of time that didn’t end for [him]”.
Stimulants can lead both humans and rats to overestimate time intervals, while depressants can have the opposite effect. The level of activity in the brain of neurotransmitters such as dopamine and norepinephrine may be the reason for this. Dopamine has a particularly strong connection with one’s perception of time. Drugs that activate dopamine receptors speed up one’s perception of time, while dopamine antagonists cause one to feel that time is passing slowly.
Effects of body temperature
Numerous experimental findings suggest that temporal order judgments of actions preceding effects can be reversed under special circumstances. Experiments have shown that sensory simultaneity judgments can be manipulated by repeated exposure to non-simultaneous stimuli. In an experiment conducted by David Eagleman, a temporal order judgment reversal was induced in subjects by exposing them to delayed motor consequences. In the experiment, subjects played various forms of video games. Unknown to the subjects, the experimenters introduced a fixed delay between the mouse movements and the subsequent sensory feedback. For example, a subject may not see a movement register on the screen until 150 milliseconds after the mouse had moved. Participants playing the game quickly adapted to the delay and felt as though there was less delay between their mouse movement and the sensory feedback. Shortly after the experimenters removed the delay, the subjects commonly felt as though the effect on the screen happened just before they commanded it. This work addresses how the perceived timing of effects is modulated by expectations, and the extent to which such predictions are quickly modifiable. In an experiment conducted by Haggard and colleagues in 2002, participants pressed a button that triggered a flash of light – at a distance – after a slight delay of 100 milliseconds. By repeatedly engaging in this act, participants had adapted to the delay (i.e., they experienced a gradual shortening in the perceived time interval between pressing the button and seeing the flash of light). The experimenters then showed the flash of light instantly after the button was pressed. In response, subjects often thought that the flash (the effect) had occurred before the button was pressed (the cause). Additionally, when the experimenters slightly reduced the delay, and shortened the spatial distance between the button and the flash of light, participants had often claimed again to have experienced the effect before the cause.
Several experiments also suggest that temporal order judgement of a pair of tactile stimuli, delivered in rapid succession, one to each hand, is noticeably impaired (i.e., misreported) by crossing the hands over the midline. However, congenitally blind subjects showed no trace of temporal order judgement reversal after crossing the arms. These results suggest that tactile signals taken in by the congenitally blind are ordered in time without being referred to a visuo-spatial representation. Unlike the congenitally blind subjects, the temporal order judgements of the late-onset blind subjects were impaired when crossing the arms to a similar extent as non-blind subjects. These results suggest that the associations between tactile signals and visuo-spatial representation is maintained once it is accomplished during infancy. Some research studies have also found that the subjects showed reduced deficit in tactile temporal order judgements when the arms were crossed behind their back than when they were crossed in front.
In an experiment, participants were told to stare at an “x” symbol on a computer screen whereby a moving blue doughnut-like ring repeatedly circled the fixed “x” point. Occasionally, the ring would display a white flash – for a split second – that physically overlapped the ring’s interior. However, when asked what was perceived, participants responded that they saw the white flash lagging behind the center of the moving ring. In other words, despite the reality that the two retinal images were actually spatially aligned, the flashed object was usually observed to trail a continuously moving object in space – a phenomenon referred to as the flash-lag effect.
The first proposed explanation, called the ‘motion extrapolation’ hypothesis, is that the visual system extrapolates the position of moving objects – but not flashing objects – when accounting for neural delays (i.e., the lag time between the retinal image and the observer’s perception of the flashing object). The second proposed explanation by David Eagleman and Sejnowski, called the ‘latency difference’ hypothesis, is that the visual system processes moving objects at a faster rate than flashed objects. In the attempt to disprove the first hypothesis, David Eagleman conducted an experiment in which the moving ring suddenly reverses directions to spin in the other way as the flashed object briefly appears. If the first hypothesis were correct, we expect that, immediately following reversal, the moving object would be lagging behind the flashed object. However, the experiment reveals the opposite – immediately following reversal, the flashed object was lagging behind the moving object. This experimental result supports of the ‘latency difference’ hypothesis. A recent study tries to reconcile these different approaches by approaching perception as an inference mechanism aiming at describing what is happening at the present time.
Effects of clinical disorders
Parkinson’s disease, schizophrenia, and attention deficit hyperactivity disorder (ADHD) have been linked to abnormalities in dopamine levels in the brain as well as to noticeable impairments in time perception. Neuropharmacological research indicates that the internal clock, used to time durations in the seconds-to-minutes range, is linked to dopamine function in the basal ganglia. Studies in which children with ADHD are given time estimation tasks shows that time passes very slowly for them. Children with Tourette’s Syndrome, for example, who need to use the pre-frontal cortex just behind the forehead to help them control their tics, are better at estimating intervals of time just over a second than other children.
In his book “Awakenings”, Oliver Sacks discusses how patients with Parkinson’s disease experience deficits in their awareness of time and tempo. For example, Mr E, when asked to clap his hands steadily and regularly did so for the first few claps before clapping faster and irregularly; culminating in an apparent freezing of motion. When he finished, Mr E asked if his observers were glad he did it correctly to which they replied “no”. Mr E was offended by this because to him, his claps were regular and steady. When given L-DOPA, these deficits are lessened or subside entirely depending on the dose. This case not only shows that Parkinson’s disease is related to time perception deficits but it also demonstrates how dopamine is involved.
Dopamine is also theorized to play a role in the attention deficits present with attention deficit hyperactivity disorder. Specifically, dopaminergic systems are involved in working memory and inhibitory processes, both of which are believed central to ADHD pathology. Children with ADHD have also been found to be significantly impaired on time discrimination tasks (telling the difference between two stimuli of different temporal lengths) and respond earlier on time reproduction tasks (duplicating the duration of a presented stimulus) than controls.
Along with other perceptual abnormalities, it has been noted by psychologists that schizophrenia patients have an altered sense of time. This was first described in psychology by Minkowski in 1927. Many schizophrenic patients stop perceiving time as a flow of causally linked events. It has been suggested that there is usually a delay in time perception in schizophrenic patients compared to normal subjects.
These defects in time perception may play a part in the hallucinations and delusions experienced by schizophrenic patients according to some studies. Some researchers suggest that “abnormal timing judgment leads to a deficit in action attribution and action perception.”