Chapter 3
Time – The Ultimate Illusion
How Do Our Brains Process Time?
For us believing physicists the distinction between past, present and future is only an illusion, if a stubborn one
― Albert Einstein
Our Brain’s Video Camera
To our mind, the world appears to be smooth and continuous. When we say that the world is continuous, we mean that it is persistently active and constantly undergoing change. However, neuroscientists have accumulated a sizeable amount of evidence indicating that the way we perceive reality and process sensory information is not continuous, but discrete. In other words, it seems that our brains do not process reality as a continuous stream but rather in distinct chunks, or mental snapshots, each having a short duration, similar to how a video camera records a sequence of still snapshots on film. When you observe a fast-moving car, you might see it as smooth and continuous, but recent evidence shows that this is illusive! Our experience of the world only appears continuous in the same way that a movie appears continuous, even though it is made up of detached motionless images that are replayed at a fast speed to give the illusion of continuity. The speed at which we experience the flow of time has much to do with the speed at which these mental snapshots flow inside our brain.
Buddhists’ holy texts were among the earliest sources to propose that consciousness is not continuous, but consists of a sequence of extremely fast discrete events referred to as “momentary collections of mental phenomena” or “distinct moments.” Numerous philosophers also put forward similar notions, such as David Hume, in the 18th century, who noted that the stream of our thoughts is “nothing but a bundle or collection of different perceptions, which succeed each other with an inconceivable rapidity. The mind is a kind of theatre, where several perceptions successively make their appearance.” 16
The speed of thought is the speed at which these perceptions are processed in the brain. This is known as the discrete perception hypothesis, or mental snapshot hypothesis. Over the past 50 years it has fallen out of favor because a substantial portion of the evidence up to that point, although provocative, was not definitive. However, in recent years, and with accumulating experimental data, the theory found renewed fervor and has regained support. The idea is based on the fact that the brain, like a video camera, seems to record reality in small discrete mental snapshots, at a recording speed of several snapshots per second, and weaves them together to give the illusion of continuous seamless motion. 17 According to Francis Crick, Nobel Prize winner, biophysicist, and co-discoverer of the DNA molecule structure, consciousness not only comes in distinct mental snapshots, but the experience of motion is itself illusory, for “perception might well take place in discrete processing epochs, perceptual moments, or snapshots. Your subjective life could be a ceaseless sequence of such snapshots.” In that sense, life is a movie, your eyes are the camera lens, and your brain is the video camera!
The Speed of Time
Since it is impossible to conceive of time without change, it is reasonable to expect a relationship between our time experience and the way we perceive change. The best way to illustrate that relationship is by using the video camera analogy. If you own one of the latest iPhone or Android smartphones, you might have noticed a video recording feature called “slo-mo,” which is used to capture fast-action scenes and render them in slow motion. In the normal video mode, a scene is usually recorded at a speed of 30 frames per second (fps) but with the slo-mo mode, the latest models now boast cameras that are fast enough to capture videos at a recording speed of 240 fps. If you switch your smartphone to that high-speed recording mode and capture a fast action scene at 240 fps, when the scene is later replayed at the normal speed of 30 fps, it will appear in to be in slow-motion, exactly as if time had slowed down. When filming at 240 fps, every second will contain 240 frames, which will be spread over eight seconds when replayed at the normal speed of 30 fps. Therefore, every second that is captured at the fast recording speed will appear eight times longer and time will seem to be running slowly.
This is similar to what happens within our brains, but of course to a much lesser extent. Let us assume that we perceive the world at an average speed of 10 mental snapshots per second. Every time our brain captures 10 snapshots, it assumes that one second has elapsed. Now imagine that your brain’s processing speed is suddenly given a boost, say from a dose of drug stimulant such as LSD or amphetamine drugs (speed). There would now be a surge in brain electrical activity which would allow for the brain to capture 20 snapshots per second. Under normal circumstances, 20 snapshots would have taken two seconds to record at the brain’s normal recording speed of 10 fps. When those 20 snapshots are processed, the brain assumes that they must have spanned a period of two seconds instead of the one “real” second that was actually needed to record them. One second of “real” time will contain two seconds worth of information and will therefore appear to have stretched, as if time had passed slowly. Such experiences, as we shall see later in more detail, have been confirmed by people who take drugs that stimulate the brain. The faster our brain is at processing sensory information, the faster mental snapshots flow in our mind, and the slower time appears to run. The speed at which we experience the speed of time is nothing but the speed of our thoughts. To measure how fast time runs in your mind, check this interesting free online Speed of Time test at http://www.subscribepage.com/speed-of-time-test.
The converse can also explain how in certain situations time seems to fly. In the 1920s, in the early days of movie making, silent films were recorded at a slow speed of 16 frames per second and had to be replayed at much higher frame rates to look continuous and real. This made the movie appear as if it was in fast-forward mode. Charlie Chaplin style movies are a perfect case in point; everything moves literally faster than normal, as if time was running fast. This analogy helps us understand what goes on in the brain when it records fewer mental snapshots per second, say five fps instead of the normal 10 fps, for the sake of demonstration. This means it will need two seconds to capture the 10 snapshots it normally captures in one second. When those 10 snapshots are processed, the brain assumes that the two seconds it took to capture them is a single second. At that rate, two minutes will seem like one minute and the day will be over before you know it. The slower your brain is in processing sensory information, the faster time seems to run. This seemingly inverse relationship is important to understand why we sometimes experience time as speeding up or slowing down. So how fast are we actually processing reality?
“The slower your brain is at processing sensory information, the faster time seems to run, and vice versa”
How Long Is a Mental Snapshot?
The brain’s processing speed is directly linked to the duration of our mental snapshots. The shorter the snapshots, the faster information is processed. One clue for the duration of a mental snapshot comes from what psychologists call the phi phenomenon, also known as “apparent motion.” Suppose two circles are flashed successively at two separate locations on a computer screen. If the time interval between them is short enough, we will not be able to distinguish them successively, and the circles will appear simultaneously. As we saw earlier, this has to do with the time needed for sensory signals to register in our brain. However, if the interval is increased to at least 50 milliseconds, or 20 flashes per second, something quite dramatic occurs: one of the circles will appear to move smoothly to the other circle in an alternating back and forth motion, despite the fact that the circles are really just flashing on and off at their fixed locations. The perceived motion of the circle is entirely supplied by our brain, which is happy to fill in the blanks. This is very fortunate for movie lovers, since this phenomenon is not just confined to flashing circles but extends to complex sequence of still images that make up a movie. This phenomenon gives a clue on how the brain manages to perceive continuous motion from a sequence of mental snapshots.
In movies,
the faster the recording speed, the closer the motion on film is to reality. Modern VHS and digital video recording technologies usually record movies at 24 frames per second (fps). TVs operate at 30 fps and computer monitors at 60 fps. Actually, anything above 10 fps, i.e. one frame every 100 milliseconds, will give the illusion of smooth continuous motion. When The Hobbit was released at a frame rate of 48 fps, it caused uproar in the movie industry and among some moviegoers who found it to be too real! Replay that movie at a speed of less than 10 fps and motion will appear jerky. The movie will start to look like a quick slide show and the illusion of continuous motion disappears. This 10 fps critical recording speed implies that in order for our brains to perceive a sense of continuity in motion, film snapshots should not be more than 100 milliseconds apart. But what is so special about that short time interval of 100 milliseconds?
In 1860, the biologist Karl Ernst von Baer gave an important lecture to the Russian Academy of Sciences in St. Petersburg, where he introduced the notion of a “life moment” as shortest time interval that can be perceived by a living being. 18 Von Baer suspected that different animal species, having different brain sizes and sensory organs, most likely had different durations for their “life moments.” This meant that they experienced the flow of time at different speeds. For von Baer, the most important bodily process for time perception was the speed at which our sensory organs can detect new sensations. Based on early experiments, he speculated that humans could enjoy around 10 “life moments” or mental snapshots within one second (this would be less for other species, such as turtles or snails). From that, he concluded that the length of a human “moment” is not more than 100 milliseconds, the same duration that creates the illusion of continuity in movies.
Time durations in the range of 100 milliseconds appear to form basic units of human consciousness and play an important role in how the brain operates. Take a small object, say a key, tie it to a string and twirl it rapidly. If it makes a full turn in less than a tenth of a second, or 100 milliseconds, it will seem as if it is equally spread out in a closed circle. When you slow down the rotating speed, you will see the key again distinctly and the closed circle disappears. Rotating the string at a speed of 10 turns per second gives the illusion of continuous motion, similar to the minimum recording speed needed to produce continuous motion on film. As Nobel Prize winner and physiologist, Charles Richet, wrote: “An elementary mental vibration has a certain duration, and that duration is approximately a tenth of a second.” He believed that this duration was a measure of the speed of our thoughts. Other evidence comes from the average reading speed. Try to read as many words as you can in 10 seconds and you will notice that, despite your best efforts, the number is about a hundred—one word every tenth of a second. One tenth of a second also appears to be the shortest time interval for taking an action and appears in many reaction time experiments, as we saw earlier. The 100-millisecond time interval appears to be a fundamental feature of our brain’s information processing speed.
Shortly after Von Baer’s speculation, scientists started conducting all sorts of experiments to determine the duration of mental snapshots in order to determine how fast our brains “record” reality. In 1903, Professor J.P. Hylan concluded that when people are presented with six consecutive letters popping up on a screen, they will appear simultaneous if they fall within an interval of approximately 80 milliseconds, and that they can only be perceived distinctly if they are spread out over a longer interval of time. 19 In an effort to measure these mental snapshots or “perceptual moments,” psychologist G.A Brecher devised an ingenious set of experiments that established the minimum time required for the brain to distinctly perceive two or more events presented in sequence. His estimates were on average 57 milliseconds. Any two distinct events falling within that time interval would be perceived as occurring simultaneously. Further research confirmed that sensory signals, whether visual, auditory, or touch, will only appear to be successive if they are separated by a minimum interval that ranges from 25 to 100 milliseconds.
We, therefore, cannot detect more than 10 to 40 sensory stimulations per second, which is quite close to the 10 “life moments” estimated by Von Baer more than a hundred years earlier. In light of all that, psychologist J.M. Stroud introduced the notion of the “discrete moment” or mental snapshot, and concluded that in order to distinguish between two events, the time interval between them should be around 100 milliseconds long. 20 Each mental snapshot is associated with a mental impression of color, motion, sound and so on, captured from the senses.
Measuring Mental Snapshots With Flickering Lights
To measure the duration of our mental snapshots, scientists use flickering lights to assess the number of visual events that can be distinctly identified each second. Imagine you are observing a flickering light source that is emitting, say, five flashes per second. You can easily see each individual flash clearly separated by fleeting instants of darkness. However, as you start to increase the rate of flicker, you will reach a frequency where you can no longer distinguish the distinct flashes and instead start seeing a steady or continuous light. That critical flickering speed is called the Flicker Fusion Frequency (FFF) and is a measure of our brain’s “recording” speed. At that flickering frequency, your brain can no longer perceive the instants of darkness that separate the flashes and they fuse into a constant steady light.
Scientists have been measuring FFF values in humans for decades and have arrived at a range of 10 to 40 flashes per second (fps). 21 Brain “recording” speeds have also been found to vary among animal species. Von Baer was right when he suggested, back in 1862, that different animals experience different flow of subjective time, depending on their size. Like humans, the speed at which animals perceive reality depends on how rapidly their nervous system can process sensory information. As explained above, this can be assessed by measuring the speed at which a fast-flickering light cannot be distinguished anymore and appears continuous. Generally, the smaller the animal and the faster its metabolic rate, the faster it can detect the flickering light, the faster information can be processed, and the slower time passes. Have you ever wondered how birds manage to chase one another through a forest at lightning speeds without colliding with branches or ending up splattered against a tree? Animals smaller than us see the world in slow motion. That is how birds manage to avoid smashing into trees. Scientists, for instance, found that a pigeon’s brain can record up to 100 frames per second (fps) and ground squirrels can grasp 120 fps. 22 A higher FFF gives animals an advantage when pursuing a fast-moving target. Pigeons rely on the high recording speed to flee from a predator, dive down to snatch prey, or zero in on a nest for precise landing. It allows them those few extra seconds to peck at seeds on the road and fly away at the last possible moment before a car approaches.
Dogs can also process visual information at least 25% faster than humans. If you own a dog, you may be surprised to know that when your pet is sitting next to you watching TV, it sees a flickering screen. That is because TVs flicker at 30 Hz but provide the illusion of continuous images because of our lower temporal resolution compared to the higher frequencies at which they operate. Dogs, however, can detect that flicker because their visual system has a higher refresh rate than that of TV screens. You might think they are enjoying the movie, but all they can see is constant flicker—they just enjoy your company! For them it would probably be more enjoyable if the movie was played on a computer monitor because of its higher flickering frequency (60 Hz). Similar studies on shark vision have revealed that they experience flicker fusion at about 45 fps, nearly twice the frequency at which humans cease to see distinct flashes. Chickens can perceive flickering at around 90 fps. This means they can easily detect the flickering of florescent lamps that are generally used to artificially illuminate poultry housing farms, creating unnecessary and constant stress for these poor animals.
The highest FFFs in animals belong to insects, like houseflies and honeybees,
which can perceive motion at the colossal rate of up to 300 fps. This remarkable recording speed is what makes it so hard to hit a housefly with a rolled-up newspaper. The fly perceives the swift strike in “bullet time,” similar to a slow-motion action scene in movies like The Matrix. For a fly, time runs at least 20 times more slowly than it does for humans. This gives it ample time to escape and easily evade the strike in the same way that Keanu Reeves evades the bullets in that famous scene. Flies might not be deep thinkers, but they can make good decisions extremely quickly.
At the other end of the spectrum, lower Flicker Fusion Frequencies can be found in animal species that have a slower pace of life. The leatherback sea turtle, for instance, has an FFF of just 14 fps. 22 The lowest known FFF belongs to a deep-sea creature (the Booralana Tricarinata) which boasts only 4 fps. Its temporal resolution is so low that it is unlikely to track any moving objects. For these species, life looks like one brief and boring slide show!
The Power of Time Perception Page 5