Humans identify and judge qualities such as size and distance by comparing qualities and objects, and how this can lead to errors in perception.
Circles A and B are the same size. It is the surrounding grey circles that make circle B appear smaller.
Human perception of objects is influenced by nearby objects, qualities, and other information. Both consciously and nonconsciously we judge things through comparison.
To measure fabric one compares the cloth to a yard stick. To judge the size of someone’s hand, you might press your palm against hers. To judge someone’s speed, you might race him or watch him race someone else.
In often less exacting comparisons, humans judge the length, height, angle, shape, color and distance by comparing one object to others in the scene. Looking at a family snapshot photo you might guess the height of a stranger by comparing him to someone you know. You will guesstimate the distance to a house by comparing its size to the sizes of closer houses and trees. You will guesstimate an angle by comparing it to a level line (“Appears to be about 10-15% off from level”).
Often these guesstimates are accurate to a reasonable degree. You might guess that stranger in the photo is 6 feet tall, as you know your aunt is 5’ 5.” When you meet him, you may discover he’s 5’10-1/2.” Not perfect, but a darn good guess—especially as you were unable to see what shoes they had been wearing.
A problem is that, while comparing to other objects is essential to making judgments, comparisons can lead to errors. Seemingly logical comparisons can produce bizarrely wrong answers. These errors happen when assumptions about an object or the overall scene are wrong.
What happens if you incorrectly remembered your aunt as 6 feet tall, instead of 5’5,” as the last time you saw her you were a five-year-old munchkin? Your calculations of the man’s height will be similarly off. You might incorrectly guess he was 6’7.” What happens if she was wearing flats in the photo, while he, shy about his height, was wearing lifts? What happens if the man couldn’t make the family reunion and a cousin photo-shopped in an image of him?
The above two horizontal lines are straight and parallel. The angled background makes them appear to bend. Without the angled background, the lines would appear parallel.
The men are the same size. Measure them yourself. It is the skewed diminishing scale lines that make them appear to be of different sizes.
There is no bulge in this checkerboard. The horizontal and vertical lines are perfectly square and even. It is the triangles in the corners of the middle squares that make it appear to bulge.
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Camouflage: Seeing But Not Perceiving
With some forms of camouflage, such as a brown chameleon standing in front of a matching brown rock, you see the chameleon but don't perceive it. Your eyes and mind receive the same visual chameleon information as when the chameleon is standing in front of a white sheet. This is how a chameleon or arctic fox can hide in open view.
Link: Invisibility : You can simultaneously see and not see things
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Questions
Does all human perception require comparison and contrast? How about all human thinking and ideas? Can a human perceive a color without contrast and comparison, including mental & memory comparison?
How do one’s education, experience, and culture play into comparison and identification?