Perception and Misperception of Movement
The concept of visually perceiving and misperceiving movement in scenes is similar to the perception and misperception of still images
The general concept of visually perceiving and misperceiving movement in scenes is similar to the perception and misperception of still images (see previous post). The viewer’s eyes take in a limited amount of information (limited by viewpoint, optical abilities, etc) and physiologically/mentally translate the information into a perception.
The human uses its complex mental template to make the final perception or judgment of what is going on. The template was formed by experience, knowledge, genetic tendencies, physiological abilities (your visual template is literally blind to the ultraviolet light that birds see, and the infrared light snakes see), personal bias, aesthetics, etc. Often the final interpretation, or perception, is a correct representation of what is being viewed. Sometimes the perception is off.
Except for more extreme situations, such as very slow movement or very small objects, the human eyes and brain are good at detecting the presence of movement in its field of view. The misperceptions most commonly happen in the interpretation of the movement. Humans can correctly detect the presence of movement, but misinterpret the speed, the direction, and even what is moving. A human can think object A is moving, when it is object B moving (see the ‘Parking lot prank’ below).
As with still images, viewers are often faced with ambiguous situations. The viewed information can be perceived in different ways, often opposing ways. The ambiguity can be because we have a limited view of a scene. A limited view can be caused by our point of view (viewing from the left or right, close or far), because the view is partially obstructed, or the capabilities of our eyesight are stretched (the object is too far away or it’s getting dark). Even with still images, these types of limitations can cause illusions.
With ambiguous, multiple-choice information, the human uses its template to pick which choice is correct. Often times the template’s pick is correct, while sometimes the pick is wrong.
The following are examples of being presented with ambiguous information and making the wrong choice about what is going on.
Parking lot prank
A prank you may have heard about is where the two pranksters park their two cars, one on each side of a parking space. Sometime later, the unsuspecting victim parks his car in the space. When the unsuspecting victim is fiddling with his keys or checking the contents of his wallet or looking in the glove compartment, the pranksters suddenly drive forward or backward in unison. The victim gets the instant sensation that it is his car moving and panics. He soon figures out what happens, and is embarrassed. This is an example where a person correctly identifies the presence of movement, but misinterprets what is moving. Also note that his misperception was instinctual, and soon corrected when he figured out what happened (“Damn kids.”).
Change of speed pitches in baseball
In baseball, pitchers use a so-called changeup pitch to fool the batter. A changeup is intended to resemble a fastball but is slower. The changeup is typically thrown after a fastball, often consecutive fastballs. Then, seeing the identical fastball arm and body motion from the pitcher, the batter believes the ball is again coming fast and swings accordingly. When the changeup works for the pitcher, the unexpected speed results in the hitter making feeble or no contact with the ball. A batter can look the fool swinging with all his might at a slow pitch.
In this case, the batter correctly perceives that the baseball is moving, but incorrectly guesses its speed. Also note that batter’s perception of speed was not based on ball movement itself, but the batter’s expectations, expectations based on experience.
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Duly note that a wrong pick doesn’t always mean it was a bad one. If it looks like someone’s about to throw a brick at you, it’s prudent to react as if he will even if he wasn’t going to. When a car moves towards you, it is not a bad idea to overestimate its speed. These and other perception choices are more about self-preservation than statistical accuracy. Also note that many instances, for example with the parking lot prank, a person must react instantly to the ambiguous information. Humans wouldn’t have lasted long on this earth if they weren’t able to react to movement automatically, instinctually, even if sometimes incorrectly.
Also note that many of the misperceptions were corrected with time and knowledge. Both the parking lot patsy and the baseball hitter corrected their misperceptions. Humans aren’t omniscient. Our perceptions are honed, corrected, and filled in by knowledge, experience, and new viewpoints.
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How we judge movement in motionless images
Judging and perceiving movement in still images illustrates how we judge movement using things other than movement itself. We use the overall scene, our experience and expectations about what is going on. Discussing the movement in motionless images (which of course is oxymoronic) reveals aspects of our template– what motionless conditions and qualities indicate movement in our minds.
Even though they are motionless, we see dogs in the act of running. Blurred ground, field, open mouths and hanging tongues and ears tilted back, all evoke the sense of movement.
Movement and direction are inferred by the blurriness of ball and background, and even how the image was cropped.
We not only perceive wind, but wind moving left to right
The tree was motionless at the moment the photo was shot, but ewehave a story about the tree’s past and future movement. We assume lightning knocked down the tree during a storm. We can also imagine the tree being chopped up and taken away.
Ambiguous movement: The Barber pole illusion
There are instances where, due to limited including obscured viewpoint, one cannot determine the direction of movement. A standard example is the candy-striped barber pole.
A barber pole has diagonal stripes and is rotated to the left or right. Looking from a particular angle it can look as if the stripes are moving straight up or down depending on the direction of rotation. Faced with different plausible choices humans unconsciously pick one.
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Stroboscopic Effect and Ambiguous Movement
While humans perceive realistic movement in the quick flashing of still images that is a movie, there is a strange, unrealistic movement they sometimes notice. In old time Westerns, the wheels of a moving wagon sometimes appear to be still, rotating slower than they should or even rotating backward. This happens when the rotation speed of the spokes is not in synchronicity with the speed of the film.
The below three still images of a wagon wheel look to show the wheel in the same position, but they show the wheel at different rotations. The middle picture is rotated 90 degrees from the left image, and the right is rotated an additional 90 degrees. That each spoke is shaped and colored identical to the others is essential to the illusion. If these were the stills in a movie, the rotating wheel would appear to be motionless. If they were the stills in a movie but the rotation was 80 degrees instead of 90, the wheels would appear to be going backwards.
The wagon wheel illusion in a movie is an example of the stroboscopic effect. In the dark, a strobe gives off intermittent flashes of light. The viewer views a moving object through short intermittent snapshots rather than a continuous view. This can lead to misperception of movement, such as with the movie wagon wheel.
Say you are watching a swinging pendulum under stroboscopic lighting. If the strobe flashes a quick burst of light once every second and it takes the pendulum exactly one second to swing back and forth, the pendulum will appear to be motionless. Each flash catches the pendulum in the same position, the pendulum having done quite a bit of moving in the dark. If the flashes catch the pendulum at its extreme right position, the pendulum will appear to being pulled or blown right.
This is an example of the human making an Occam’s razor perception from the limited information. The information is ambiguous, there are different possible explanations for what you see, and the viewer chooses the simplest explanation, the one that seems to make the most sense. If you and others saw no movement in an object, it would be considered bizarre for you to proclaim that the object was moving. However, this bizarre proclemation would be correct with the pendulum. Sometimes the simplest explanation is wrong because it is formed from limited information.
Animated advertising signs that use a grid of flashing lights give an example of how humans interpret changing information. When you look at the above, it soon appears that there is a single yellow dot moving around and around. However, it is many dots changing color, the equivalent of lights turning on and off. Bank signs and sport stadium scoreboards use this technique to create apparent animated words and characters.
Even when one knows what is happening, it is still perceived as a single moving light. The phenomenon is commonly referred to as the Phi phenomenon.
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Movies as quasi-strobe images
When watching a movie, the people or horses on the screen appear to move realistically, but are stroboscopic-like flashes of still images. To the mind, this quick succession of still images of a horse most closely matches real movement. The mind is faced with information that can be interpreted in different ways. To the mind, real movement may not be the perfect choice (the eyes detect the shuttering of the film), but it seems better than other choices.
“Close enough counts”
As the movie motion shows, visual information that is close enough to what the brain’s template detects as real can be perceived as real. When judging ambiguous information, the brain chooses what the information most closely resembles. The motion picture running horse information closely, if not totally, matches up with the brain’s template for a running horse, so is perceived as a running horse.
Neurons in our unconscious brains are used to identify and interpret movement. They help identify not only the presence of movement but also judge the direction and speed. There are still images with patterns that the neurons interpret, if only briefly, as motion. The below is an example.
Movies as quasi-strobe images is interesting and differs. For about 2/3 of dogs they perceived television as separate flashing pictures and not smooth movement.
frequency at which dogs perceive multiple flashing pictures as movement and why many donuts can't watch tv
Dogs perceive flashing images as continuous movement at a higher frequency than humans due to their superior "flicker fusion frequency." While humans require about 16–20 frames per second (Hz) to see smooth motion, dogs need at least 70–80 Hz. This means older TVs and screens with lower refresh rates appear as flickering images to dogs, rather than seamless motion.
This difference arises because dogs' retinas are optimized for detecting motion and low light, with more rod cells than cone cells. These adaptations make them excellent at spotting fast-moving objects but less adept at perceiving fine detail or vibrant colors. Consequently, many dogs may not find TV engaging, as the images appear disjointed and lack accompanying sensory elements like smell. Modern high-refresh-rate TVs may partially overcome this issue for some dogs.