In a classic scene in the science-fiction blockbuster The Matrix, life starts to run in slow motion. Guns are fired at the main character Neo, but the bullets fly as if through molasses—and our hero’s quickened reflexes allow him to jump out of harm’s way. Many of us have experienced a similar deceleration of events during accidents or other life-and-death situations. You see the tree branch on the road, hit the brakes, and it seems like an eternity before you know if you avoided the collision or were too late.
Of course, we know that physical time does not objectively slow down just because we are subjectively stressed out. But can we really think and act more quickly in a fear-provoking situation? Recently neuropsychologist David M. Eagleman of the Baylor College of Medicine decided to find out by asking psychology graduate students to jump 150 feet from a high metal scaffolding into the center of a safety net.
During their free fall his human projectiles wore displays on their wrists on which numbers appeared in rapid succession. The digital figures flickered just fast enough so that they were not legible under normal conditions. Eagleman wanted to know if the test subjects could take in more information per time interval under conditions of intense fear. In other words, would a slowing of subjective time allow them to pick out the otherwise indecipherable speeding numbers?
Not surprisingly, his students were scared out of their wits. In addition, they reported that their fall appeared to take about twice as long as it actually did. Nevertheless, they were not significantly better at reading the numbers on the display than someone under less death-defying circumstances would be.
What Eagleman’s experiment demonstrates dramatically is that the conscious human mind—despite astonishing powers of observation, cognition and reason—can be a remarkably lousy clock. Our sense of time speeds up or slows down in response to many factors, including fear and stress. Our mind easily enters such states of “temporal illusion” in which our judgment of time (and our perceived ability to dodge bullets) certainly cannot be trusted. For more than a century, cognitive scientists have been investigating the timekeeping abilities of our brain and how they relate to our conscious sense of time. Despite these efforts, understanding the underlying mechanisms remains one of the greatest challenges of modern cognitive neuroscience.
The Good Clocks The poor sense of timing demonstrated by our conscious minds is all the more puzzling because in other ways our brains prove to be rather precise chronometers. Consider, for example, the unconscious control of movements. Anyone who has ever tried tennis knows that players have just a few tenths of a second to anticipate where the ball will land, how to position their bodies and at what angle to direct their return. Other motor tasks such as walking, juggling or driving also rely on accurately timed motor actions on a subsecond scale.
The execution of such precise movements suggests that animals’ brains contain one or more biological clocks. Just like the watches that adorn our wrists and chronometers that appear on everything from car dashboards to microwave ovens, these biological clocks presumably depend on the detection and counting of periodically occurring invariant patterns. In our case, periodic salvos of nerve cell impulses in the brain—much like the beat of a metronome—make for a perfect timing signal that could be “counted” by other neurons.
In the case of movement control, a number of regions in the brain have to be coordinated to create appropriate motor actions. These regions include a network of cortical areas as well as subcortical nuclei such as the basal ganglia, but the timing or pacing information seems to originate in the cerebellum. Because of its architecture, this region is particularly suited for the task of timing. The dendritic trees of large Purkinje cells in the outer layers of the cerebellum form a parallel and evenly spaced grid through which the axons of other neurons run perpendicularly. As electrical impulses tend to run through these perpendicular axons at the same speed, motor signals can be timed and synchronized with great precision.
It is not just the sudden twitch, however, that the brain can measure accurately. Longer timescales seem to be involved as well. For instance, even when deprived of external time cues for a few days, people will complete the cycle of sleeping, waking and eating on a somewhat regular schedule. In the 1930s physiologist Hudson Hoagland, then at Clark University, hypothesized that a central clock driven by chemical processes in the body could be responsible for this regularity. But only by the early 1980s did researchers hit on a likely candidate in the brain: the suprachiasmatic nucleus (SCN).
This tiny cluster of barely more than 3,000 neurons is situated directly above the crossing of the optic nerves—more or less immediately behind the eyes—and plays a crucial role in regulating the sleep-wake cycle of the organism, which involves body temperature, hormone metabolism and general level of alertness. The SCN emits rhythmic signals to the nearby pituitary gland, which then releases messenger substances into the blood, as well as to the pineal gland, which is responsible for the production and release of melatonin. This is a natural cycle of slightly more than 24 hours—which is why it is referred to as the circadian rhythm (the Latin circa means “approximately,” and dies means “day”).
Frequent fliers and shift workers know all too well how persistent circadian rhythms can be. The symptoms of jet lag after intercontinental flights or the particular disorientation that results from working different shifts may take days to subside as the body’s natural rhythm adapts to its new surroundings or schedule.
Tell Me When The irony is that although the brain seems to have accurate biological clocks at its disposal, our mind’s eye appears unable to read them. Instead exactly how long or short a minute, an hour or a day appears to us varies dramatically and can depend on a multitude of diverse influences, including physiological factors such as body temperature and fatigue or mental disorders such as schizophrenia and depression. It has been shown that even drugs such as LSD and cocaine can have profound effects, accelerating or decelerating the subjective passage of time.
Thus, the psychological experience of time—as is the case in all other senses—can be predictably affected by our physical state. This is probably best established in the case of body temperature: high temperatures are associated with an expansion of subjective time, whereas low body temperatures correspond to a shortening of subjective time. In other words, a person with a fever is bound to experience a given period as longer than someone without the fever.
But Eagleman’s “high jump” experiment and many others demonstrate that it is easy to manipulate our temporal sense using psychological triggers, shrinking and expanding our sense of a minute or hour by simply changing sensory inputs or emotional states.
For instance, time passes very quickly whenever we are subjected to a large number of new, fast-changing or complex stimuli, such as when we are playing an engrossing video game. Presumably the limited resources of our attention are absorbed by the demands of the fast-paced perceptual situation. In contrast, during periods of low stimulation—such as when waiting in a long line or when performing routine tasks—time seems to crawl very slowly. In hindsight, matters look quite different, as British psychologist John Wearden of Keele University in England demonstrated in 2005. He showed a group of test subjects a nine-minute clip from the movie Armageddon. A second group spent the same amount of time in a waiting room without anything to do. Which group experienced time as subjectively faster? No question about it, the minutes flew by for those watching the film clip.
When the researchers questioned the test subjects again some time later, however, those who had sat in the waiting room twiddling their thumbs during the experiment estimated the time as a good 10 percent shorter than those who had watched the movie. In retrospect, an eventful period appears longer, phases of boredom shorter. What seems to be crucial is the quantity of amassed memory. Rich and varied memories are associated with long periods, less intense or similar memories with shorter ones. This neatly illustrates that the subjective experience of time arises from the interplay—some say as the by-product—of processes in attention and memory.
Three-Second Rule Yet humans estimate at least one time interval accurately. This oddly persistent ability was first described in 1868 by an early pioneer of time research, Karl von Vierordt, who dubbed this time interval the “point of indifference.” Study subjects estimated that tones shorter than three seconds in duration lasted longer than their actual duration while those longer than three seconds were reported as being shorter.
The three-second point of indifference—the interval at which the subjective impression and objective duration are about the same—has remained unchanged throughout the past century. In view of the technological and social revolutions—and cultural speedup—of the past 100 years, this consistency seems rather remarkable. Modern high-speed transportation and rapid communications make for a hurried way of life. Television and video clips accelerate our visual habits. Nevertheless, this critical three-second threshold seems to remain invariant, suggesting it is hardwired into the brain.
Some experts believe this same time window may be related to another aspect of time, our experience of the present. Brain researchers such as Ernst Poeppel of the University of Munich take this view. Poeppel coined the term “subjective present” for the narrow saddle in time of that which is not quite yet past and that which is barely not still in the future—the mental “now.”
Poeppel draws his conclusion from observations such as the following example: try to speak a series of meaningless syllables such as “ba kyoo ba kyoo ba kyoo” as fast as possible. After even a short time, the sounds will fuse into units. At some point, they will automatically remind you either of Baku, the capital of Azerbaijan, or Cuba. The semantic order does not remain constant, however; the grouping of syllables changes rather quickly from Baku to Cuba and then back again. As controlled experiments have shown, this turnaround occurs on average every three seconds.
Then and Now Another way our mind constructs our rich notion of time is illustrated by the quality of temporal order—the mind determines the order of events. Chronopsychologists have discovered some interesting features of this ability, especially in the perception of nonsimultaneity and sequence. The chronological resolution of perception determines whether two light flashes, needle pricks or sounds appear to occur separately or simultaneously. If stimuli are presented below a particular threshold—in other words, in rapid succession—they fuse together, and we experience them as synchronous or continuous.
Each sensory channel has its own so-called fusion threshold—our hearing is very acute with a chronological resolution of two milliseconds; our sense of vision, in contrast, is usually overwhelmed by 40-millisecond intervals. If this timing were not the case, the action on television screens would appear to us as rapid successions of instant snapshots instead of the smoothly moving objects that we actually perceive. It is the “lazy” visual apparatus that links these impressions together in space and time.
In addition, experiments have shown that detecting chronological synchronicity and discerning the sequences of sensory impressions are two entirely different animals. Test subjects may perceive two clicks that occur at an interval of 20 milliseconds as nonsynchronous; however, they may be unable to tell which of the two different sounds came first. For that, the stimuli need to be spaced at least 40 milliseconds apart.
Timekeeper or Follower of the Rhythm Section? It remains unclear how many parts of our brain are involved in creating our sense of time or what, exactly, they do. One of the most active areas of research has centered on identifying tissue regions that affect time estimation. Studies of patients with brain damage, for example, have revealed that if the cerebellum is partially knocked out as a result of an accident or stroke, the patient typically experiences great difficulty in the execution of fine-motor tasks—but also in the ability to identify intervals of a few seconds’ duration. If the neural insult involves the frontal lobe, a person may report that a sound lasting several seconds was nothing more than a “click.”
In a 2003 study Giacomo Koch and his co-workers at the University of Rome Tor Vergata took a different approach by distorting time-interval estimates in healthy people using transcranial magnetic stimulation. This technique focuses a strong electromagnetic field on one region of the brain, temporarily disrupting local neuronal function. These researchers found that when the frontal lobe of their subjects was targeted, subjects consistently underestimated the duration of a sound.
From this work, one thing becomes immediately apparent. Our mind does not depend on a single clock in our brain—potentially countless neuronal modules may contribute to our sense of time. More fundamentally, though, researchers debate whether any of the brain’s neuronal circuits are actually dedicated to the conscious measurement of time or if time perception mechanisms are completely diffuse throughout the brain. In support of the former idea stands a 2005 experiment conducted by neurobiologist Michael Shadlen of the University of Washington. He trained rhesus monkeys to fixate their gaze on a point on a computer screen; the point would disappear after a certain variable period. This disappearance was a signal for the animals to wait for a specified amount of time and then observe a particular section of their visual field, for which they were rewarded with fruit juice.
At the same time, Shadlen recorded the electrical activity of individual neurons in the parietal lobe or, more precisely, in the lateral intraparietal area (LIP). The researchers found that the activity pattern of these neurons was closely associated with the elapsed period as well as with the timing of anticipated rewards—they reflected the probability that the wait interval of up to several seconds would end soon. To be overly simplistic, these neurons function somewhat like an egg timer. Shadlen argues that in their natural habitats, many animals regularly seek out certain food sources, and to accomplish this task they need a cognitive representation of elapsed time. Shadlen’s report is the first description of a direct correlate of such representations—on the level of specialized nerve cells in the LIP.
Alternatively, Warren Meck of Duke University and Matthew Matell of Villanova University question the existence of specific “time neurons.” Rather they have identified a highly sensitive rhythm detector, the striatum, which is a part of the basal ganglia. Meck and Matell also trained animals (in this case, rats) to adapt to specific time intervals. If the rodents pressed on a key at the right moment, feed pellets dropped into their cage. As cell tracings of the striatum showed, the end of a learned interval was accompanied by furious bursts of activity in this region. But these researchers believe this activity is the result of the striatum sampling signals from across the brain—as suggested by the fact that the basal ganglia are closely connected to most cortical brain areas. Meck and Matell compare the brain to a symphony orchestra during a concert, with the striatum in the role of the listener; the recurrence of periodic patterns in the music indicates when a learned time interval has come to an end.
In other words, they suggest that there is no dedicated stopwatch. Our sense of time comes about as a result of the flurry of rhythmic activities that the brain carries out for other reasons, in line with the psychological research showing that attention and memory effects can easily distort the time experience. The problem with this model, however, is that in the symphony of the brain, myriad voices sing in unison at any given time. What enables the striatum to recognize that one periodic convergence is more significant than another? This question is open for future research.
Open Field The debate surrounding the existence of dedicated timekeeping neurons highlights a characteristic of time perception research that makes it exciting to follow and participate in: it is one area of cognitive neuroscience in which fundamental questions still remain to be answered. In contrast, scientists had established the existence of dedicated neurons for various visual functions, along with analogous neurons in other senses, years or even decades ago. In the next few years, advances in brain imaging and other techniques are expected to yield new important insights for time researchers in this respect.
We may never really know, however, why evolution endowed us with several highly dependable senses that are true marvels of neural engineering but left us with a sense of the passage of time that is so easily distorted. Although all evolutionary explanations are highly speculative, I will suggest one possible reason. Each passing second represents a finite resource of opportunity in the life of an organism. If I am a food gatherer and spend hours without bagging some dinner, the slow drag of dull moments helps to alert me to move on and cut my losses. On the other hand, if I am finding food in every corner, the hours will fly by like minutes, and I am happy to keep stuffing my sack. So this elastic sense of time could plausibly help animals manage their activities better than an exact one would. It is something to think about, when you find yourself with time on your hands.
Of course, we know that physical time does not objectively slow down just because we are subjectively stressed out. But can we really think and act more quickly in a fear-provoking situation? Recently neuropsychologist David M. Eagleman of the Baylor College of Medicine decided to find out by asking psychology graduate students to jump 150 feet from a high metal scaffolding into the center of a safety net.
During their free fall his human projectiles wore displays on their wrists on which numbers appeared in rapid succession. The digital figures flickered just fast enough so that they were not legible under normal conditions. Eagleman wanted to know if the test subjects could take in more information per time interval under conditions of intense fear. In other words, would a slowing of subjective time allow them to pick out the otherwise indecipherable speeding numbers?
Not surprisingly, his students were scared out of their wits. In addition, they reported that their fall appeared to take about twice as long as it actually did. Nevertheless, they were not significantly better at reading the numbers on the display than someone under less death-defying circumstances would be.
What Eagleman’s experiment demonstrates dramatically is that the conscious human mind—despite astonishing powers of observation, cognition and reason—can be a remarkably lousy clock. Our sense of time speeds up or slows down in response to many factors, including fear and stress. Our mind easily enters such states of “temporal illusion” in which our judgment of time (and our perceived ability to dodge bullets) certainly cannot be trusted. For more than a century, cognitive scientists have been investigating the timekeeping abilities of our brain and how they relate to our conscious sense of time. Despite these efforts, understanding the underlying mechanisms remains one of the greatest challenges of modern cognitive neuroscience.
The Good Clocks The poor sense of timing demonstrated by our conscious minds is all the more puzzling because in other ways our brains prove to be rather precise chronometers. Consider, for example, the unconscious control of movements. Anyone who has ever tried tennis knows that players have just a few tenths of a second to anticipate where the ball will land, how to position their bodies and at what angle to direct their return. Other motor tasks such as walking, juggling or driving also rely on accurately timed motor actions on a subsecond scale.
The execution of such precise movements suggests that animals’ brains contain one or more biological clocks. Just like the watches that adorn our wrists and chronometers that appear on everything from car dashboards to microwave ovens, these biological clocks presumably depend on the detection and counting of periodically occurring invariant patterns. In our case, periodic salvos of nerve cell impulses in the brain—much like the beat of a metronome—make for a perfect timing signal that could be “counted” by other neurons.
In the case of movement control, a number of regions in the brain have to be coordinated to create appropriate motor actions. These regions include a network of cortical areas as well as subcortical nuclei such as the basal ganglia, but the timing or pacing information seems to originate in the cerebellum. Because of its architecture, this region is particularly suited for the task of timing. The dendritic trees of large Purkinje cells in the outer layers of the cerebellum form a parallel and evenly spaced grid through which the axons of other neurons run perpendicularly. As electrical impulses tend to run through these perpendicular axons at the same speed, motor signals can be timed and synchronized with great precision.
It is not just the sudden twitch, however, that the brain can measure accurately. Longer timescales seem to be involved as well. For instance, even when deprived of external time cues for a few days, people will complete the cycle of sleeping, waking and eating on a somewhat regular schedule. In the 1930s physiologist Hudson Hoagland, then at Clark University, hypothesized that a central clock driven by chemical processes in the body could be responsible for this regularity. But only by the early 1980s did researchers hit on a likely candidate in the brain: the suprachiasmatic nucleus (SCN).
This tiny cluster of barely more than 3,000 neurons is situated directly above the crossing of the optic nerves—more or less immediately behind the eyes—and plays a crucial role in regulating the sleep-wake cycle of the organism, which involves body temperature, hormone metabolism and general level of alertness. The SCN emits rhythmic signals to the nearby pituitary gland, which then releases messenger substances into the blood, as well as to the pineal gland, which is responsible for the production and release of melatonin. This is a natural cycle of slightly more than 24 hours—which is why it is referred to as the circadian rhythm (the Latin circa means “approximately,” and dies means “day”).
Frequent fliers and shift workers know all too well how persistent circadian rhythms can be. The symptoms of jet lag after intercontinental flights or the particular disorientation that results from working different shifts may take days to subside as the body’s natural rhythm adapts to its new surroundings or schedule.
Tell Me When The irony is that although the brain seems to have accurate biological clocks at its disposal, our mind’s eye appears unable to read them. Instead exactly how long or short a minute, an hour or a day appears to us varies dramatically and can depend on a multitude of diverse influences, including physiological factors such as body temperature and fatigue or mental disorders such as schizophrenia and depression. It has been shown that even drugs such as LSD and cocaine can have profound effects, accelerating or decelerating the subjective passage of time.
Thus, the psychological experience of time—as is the case in all other senses—can be predictably affected by our physical state. This is probably best established in the case of body temperature: high temperatures are associated with an expansion of subjective time, whereas low body temperatures correspond to a shortening of subjective time. In other words, a person with a fever is bound to experience a given period as longer than someone without the fever.
But Eagleman’s “high jump” experiment and many others demonstrate that it is easy to manipulate our temporal sense using psychological triggers, shrinking and expanding our sense of a minute or hour by simply changing sensory inputs or emotional states.
For instance, time passes very quickly whenever we are subjected to a large number of new, fast-changing or complex stimuli, such as when we are playing an engrossing video game. Presumably the limited resources of our attention are absorbed by the demands of the fast-paced perceptual situation. In contrast, during periods of low stimulation—such as when waiting in a long line or when performing routine tasks—time seems to crawl very slowly. In hindsight, matters look quite different, as British psychologist John Wearden of Keele University in England demonstrated in 2005. He showed a group of test subjects a nine-minute clip from the movie Armageddon. A second group spent the same amount of time in a waiting room without anything to do. Which group experienced time as subjectively faster? No question about it, the minutes flew by for those watching the film clip.
When the researchers questioned the test subjects again some time later, however, those who had sat in the waiting room twiddling their thumbs during the experiment estimated the time as a good 10 percent shorter than those who had watched the movie. In retrospect, an eventful period appears longer, phases of boredom shorter. What seems to be crucial is the quantity of amassed memory. Rich and varied memories are associated with long periods, less intense or similar memories with shorter ones. This neatly illustrates that the subjective experience of time arises from the interplay—some say as the by-product—of processes in attention and memory.
Three-Second Rule Yet humans estimate at least one time interval accurately. This oddly persistent ability was first described in 1868 by an early pioneer of time research, Karl von Vierordt, who dubbed this time interval the “point of indifference.” Study subjects estimated that tones shorter than three seconds in duration lasted longer than their actual duration while those longer than three seconds were reported as being shorter.
The three-second point of indifference—the interval at which the subjective impression and objective duration are about the same—has remained unchanged throughout the past century. In view of the technological and social revolutions—and cultural speedup—of the past 100 years, this consistency seems rather remarkable. Modern high-speed transportation and rapid communications make for a hurried way of life. Television and video clips accelerate our visual habits. Nevertheless, this critical three-second threshold seems to remain invariant, suggesting it is hardwired into the brain.
Some experts believe this same time window may be related to another aspect of time, our experience of the present. Brain researchers such as Ernst Poeppel of the University of Munich take this view. Poeppel coined the term “subjective present” for the narrow saddle in time of that which is not quite yet past and that which is barely not still in the future—the mental “now.”
Poeppel draws his conclusion from observations such as the following example: try to speak a series of meaningless syllables such as “ba kyoo ba kyoo ba kyoo” as fast as possible. After even a short time, the sounds will fuse into units. At some point, they will automatically remind you either of Baku, the capital of Azerbaijan, or Cuba. The semantic order does not remain constant, however; the grouping of syllables changes rather quickly from Baku to Cuba and then back again. As controlled experiments have shown, this turnaround occurs on average every three seconds.
Then and Now Another way our mind constructs our rich notion of time is illustrated by the quality of temporal order—the mind determines the order of events. Chronopsychologists have discovered some interesting features of this ability, especially in the perception of nonsimultaneity and sequence. The chronological resolution of perception determines whether two light flashes, needle pricks or sounds appear to occur separately or simultaneously. If stimuli are presented below a particular threshold—in other words, in rapid succession—they fuse together, and we experience them as synchronous or continuous.
Each sensory channel has its own so-called fusion threshold—our hearing is very acute with a chronological resolution of two milliseconds; our sense of vision, in contrast, is usually overwhelmed by 40-millisecond intervals. If this timing were not the case, the action on television screens would appear to us as rapid successions of instant snapshots instead of the smoothly moving objects that we actually perceive. It is the “lazy” visual apparatus that links these impressions together in space and time.
In addition, experiments have shown that detecting chronological synchronicity and discerning the sequences of sensory impressions are two entirely different animals. Test subjects may perceive two clicks that occur at an interval of 20 milliseconds as nonsynchronous; however, they may be unable to tell which of the two different sounds came first. For that, the stimuli need to be spaced at least 40 milliseconds apart.
Timekeeper or Follower of the Rhythm Section? It remains unclear how many parts of our brain are involved in creating our sense of time or what, exactly, they do. One of the most active areas of research has centered on identifying tissue regions that affect time estimation. Studies of patients with brain damage, for example, have revealed that if the cerebellum is partially knocked out as a result of an accident or stroke, the patient typically experiences great difficulty in the execution of fine-motor tasks—but also in the ability to identify intervals of a few seconds’ duration. If the neural insult involves the frontal lobe, a person may report that a sound lasting several seconds was nothing more than a “click.”
In a 2003 study Giacomo Koch and his co-workers at the University of Rome Tor Vergata took a different approach by distorting time-interval estimates in healthy people using transcranial magnetic stimulation. This technique focuses a strong electromagnetic field on one region of the brain, temporarily disrupting local neuronal function. These researchers found that when the frontal lobe of their subjects was targeted, subjects consistently underestimated the duration of a sound.
From this work, one thing becomes immediately apparent. Our mind does not depend on a single clock in our brain—potentially countless neuronal modules may contribute to our sense of time. More fundamentally, though, researchers debate whether any of the brain’s neuronal circuits are actually dedicated to the conscious measurement of time or if time perception mechanisms are completely diffuse throughout the brain. In support of the former idea stands a 2005 experiment conducted by neurobiologist Michael Shadlen of the University of Washington. He trained rhesus monkeys to fixate their gaze on a point on a computer screen; the point would disappear after a certain variable period. This disappearance was a signal for the animals to wait for a specified amount of time and then observe a particular section of their visual field, for which they were rewarded with fruit juice.
At the same time, Shadlen recorded the electrical activity of individual neurons in the parietal lobe or, more precisely, in the lateral intraparietal area (LIP). The researchers found that the activity pattern of these neurons was closely associated with the elapsed period as well as with the timing of anticipated rewards—they reflected the probability that the wait interval of up to several seconds would end soon. To be overly simplistic, these neurons function somewhat like an egg timer. Shadlen argues that in their natural habitats, many animals regularly seek out certain food sources, and to accomplish this task they need a cognitive representation of elapsed time. Shadlen’s report is the first description of a direct correlate of such representations—on the level of specialized nerve cells in the LIP.
Alternatively, Warren Meck of Duke University and Matthew Matell of Villanova University question the existence of specific “time neurons.” Rather they have identified a highly sensitive rhythm detector, the striatum, which is a part of the basal ganglia. Meck and Matell also trained animals (in this case, rats) to adapt to specific time intervals. If the rodents pressed on a key at the right moment, feed pellets dropped into their cage. As cell tracings of the striatum showed, the end of a learned interval was accompanied by furious bursts of activity in this region. But these researchers believe this activity is the result of the striatum sampling signals from across the brain—as suggested by the fact that the basal ganglia are closely connected to most cortical brain areas. Meck and Matell compare the brain to a symphony orchestra during a concert, with the striatum in the role of the listener; the recurrence of periodic patterns in the music indicates when a learned time interval has come to an end.
In other words, they suggest that there is no dedicated stopwatch. Our sense of time comes about as a result of the flurry of rhythmic activities that the brain carries out for other reasons, in line with the psychological research showing that attention and memory effects can easily distort the time experience. The problem with this model, however, is that in the symphony of the brain, myriad voices sing in unison at any given time. What enables the striatum to recognize that one periodic convergence is more significant than another? This question is open for future research.
Open Field The debate surrounding the existence of dedicated timekeeping neurons highlights a characteristic of time perception research that makes it exciting to follow and participate in: it is one area of cognitive neuroscience in which fundamental questions still remain to be answered. In contrast, scientists had established the existence of dedicated neurons for various visual functions, along with analogous neurons in other senses, years or even decades ago. In the next few years, advances in brain imaging and other techniques are expected to yield new important insights for time researchers in this respect.
We may never really know, however, why evolution endowed us with several highly dependable senses that are true marvels of neural engineering but left us with a sense of the passage of time that is so easily distorted. Although all evolutionary explanations are highly speculative, I will suggest one possible reason. Each passing second represents a finite resource of opportunity in the life of an organism. If I am a food gatherer and spend hours without bagging some dinner, the slow drag of dull moments helps to alert me to move on and cut my losses. On the other hand, if I am finding food in every corner, the hours will fly by like minutes, and I am happy to keep stuffing my sack. So this elastic sense of time could plausibly help animals manage their activities better than an exact one would. It is something to think about, when you find yourself with time on your hands.
