These posts make more sense when read in order.
Please click here for the first article in this series to enter the rabbit hole.
We, and monkeys, see the world as continuous, but, in a way, this too is an illusion because our brains don’t process it that way. There are several reasons this happens. First, our attention is in waves that pulse at the rate of four times a second. The peaks are focused awareness and the troughs are of broad situational awareness.[1]
Your eyes blink around ten times a minute. During each blink everything goes dark, but you’re not aware of it. Even though your brain processes your blinks, it blocks it from your awareness, so our vision appears constant and uninterrupted.
It also happens when our eyes rapidly flit around a scene, focusing on different aspects and adding details to our vision. These movements are called saccades, and we average three or four of them per second—each lasting only from a fiftieth to a fifth of a second (20 and 200 milliseconds). Even though they are rapid, someone looking into your eyes can see them, but if we look in the mirror, we can’t see our own eyes do it because we’re blind when they occur.
It’s these brief periods of blindness that make the second hand on a clock appear to stand still for a moment when you first look at it. When our saccade blindness ends and we first see the second hand, our brains backfill that blind period with the new image, making the second hand appear to pause longer than it should. Your brain is predicting what it thinks you should have seen and projects it about a twentieth of a second (50 milliseconds) back in time making you believe you saw something that you didn’t see.[2]
While these periods of blindness are brief, they do add up. With three or four saccades a second, each blocking out about a tenth of a second, it means we’re blind for roughly 35% of our waking hours. And that doesn’t include blinking or microsaccade blindness. On the other hand, the saccades of your left and right eyes might not overlap all the time, reducing that figure. While our eyes usually focus together on objects, sometimes they don’t, such as when you read. Then each eye looks at a different word.
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| Donny Leonardi. |
Some of the best athletes are able to suppress saccades when they focus on a ball before and during their strike, whether in golf, tennis, soccer, baseball, or pool. Or it could be the puck in hockey or the bullseye in archery, pistol shooting, or throwing darts. In basketball free throws, it’s the front of the hoop’s rim they focus on. Called the “quiet eye”, it aids in the elimination of distractions, and the longer and steadier their focus, the better their performance.[3] Try it sometime.
There are also indications that the length of the pauses between saccades might be responsible for dyslexia.[4]
Cats, dogs, movies, and TV
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| Runner1616. |
You’ve probably noticed in old Westerns that the wheels of wagons appear to rotate backwards. It’s not the movie that causes this—it’s your brain. Your brain realizes that by moving the spokes the other way, the movement is smoother. Also, that our brains often apply corrections retroactively may have something to do with it. Unfortunately, our visual system doesn’t realize that this is unrealistic.[5]
Have you ever taken a pencil by the tip and shaken it up and down? The pencil appears to bend like it’s made of rubber. This is because most of us have the slow flicker fusion rate, which is the rate at which we stop seeing a movie as flickering still pictures and we begin seeing it as smooth motion. For humans it’s 30 to 55 frames per second (fps), although up to 72 fps might be possible. The pencil illusion doesn’t work for birds and many other animals. They see the waving pencil as remaining straight, since their flicker rate is faster. Wave your hand in front of your face and it’s a blur, but not to them. Florescent lights look steady to us most of the time, but to a chicken it’s a strobe light.
Our slow rate is probably because it takes us longer to process visual data. Also, our heads are larger so it takes longer to move the data around. A fly’s visual system has evolved for rapidity. To them, we move in slow motion. The fastest flies process 400 fps—about ten times faster than us. Most houseflies have a rate of 270 fps. That’s fast enough to escape our hand, but not a flyswatter, although you can sneak up on them if you move very slowly so that you blend in with the background. Some perching birds see 146 fps, which is the upper limit for vertebrates. Bumblebees see the world five times faster than us, but it takes them twice as long to process colors.
Because animals with small brains process information faster than us, time runs slower for them and they experience us moving in slow motion. Swordfish are able to increase their flicker rate and slow down their perception of time by boosting the supply of blood to their brains.
The refresh rate for most TVs and computer monitors is 60 hertz (cycles per second), although some higher end monitors are up to 120 hz, but that only matters in certain situations, since most movies and videos have only 24 frames per second. This is manipulated to make it work at 60 fps, but that doesn’t enhance the image though it can make blinks seem smoother. If the rate is below 20, then we start seeing individual images.
Animals that are active during the day tend to have slower flicker rates than nocturnal creatures. Cats and dogs have higher flicker
fusion rates than us, mainly because they have more rods and rods are faster. For cats it’s 70 Hz and dogs it’s 80 Hz, which would make anything but the highest end TVs pretty horrible for them to watch.At the other end of the spectrum, scallops’ eyes can only see one to five fps, while nocturnal toads see only one quarter to half a frame per second.
Flicker fusion rates are influenced by a number of things, such as an animal’s size, their metabolic rates, and how quick they have to be to catch their food. A falcon has to be faster than a bird that eats seeds, and slugs are generally slower than most people. So the perception of time probably varies considerably.
Click here for the next article in this series:
[1] Princeton University, “The spotlight of attention is more like a strobe light”, ScienceDaily, August 22, 2018,
[2] Graham Lawton, “Mind tricks: Six ways to explore your brain”, New Scientist, no. 2622, September
And
Roger Highfield, “Your kitchen sink, and 16 other wonders of the cosmos”, New Scientist, February 21, 2011, no. 2800, pp. 34-41, www.newscientist.com/article/mg20928001.400-your-kitchen-sink-and-16-other-wonders-of-the-cosmos.html.[3] David Robson, “Why athletes need a ‘quiet eye’ ”, BBC Future, June 24, 2020, https://www.bbc.com/future/article/20180627-is-quiet-eye-the-secret-to-success-for-athletes.
[4] Concordia University. “Eye movements of those with dyslexia reveal laborious and inefficient reading strategies: Researchers find that people with the learning disorder sample visual material slower and with more difficulty”, ScienceDaily, April 28, 2021, www.sciencedaily.com/releases/2021/04/210428162541.htm, citing Léon Franzen, Zoey Stark, and Aaron P. Johnson, “Individuals with dyslexia use a different visual sampling strategy to read text”, Scientific Reports, 2021; 11 (1), https://doi.org/10.1038/s41598-021-84945-9.
[5] Donald D. Hoffman, Visual Intelligence, New York: W. W. Norton & Co., 1998, p. 150.
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