In a paper presented at an international conference in rock art in , Caldwell displayed multiple examples of cave drawings and engravings that could be interpreted as portrayals of either woolly mammoths or bison. Caldwell posited that the physical similarities between the two animal shapes made them ideal candidates for prehistoric artists to superimpose their respective images in the same depiction. Whereas we do not have access to the inner thoughts or motivations of paleolithic artists—making contemporary interpretations of their artwork unavoidably inconclusive—recorded history provides us with definite proof that people have noticed, and been intrigued, by illusions for thousands of years.
The ancient Greek philosopher Aristotle BC wrote the first known descriptions of perceptual illusory in his Parva Naturalia short treatises on nature. One of his most successful inventions, described in his books Pneumatica and Automata , was an automatic way to open doors, which he implemented in sacred temples to create the fantasy of divine intervention. Columns in Greek Doric temples tend to bulge slightly in the middle, an architectonic feature known as entasis.
Historians have suggested that the purpose of the subtle convexity is to compensate for the illusory slimming that would otherwise occur with perfectly vertical columns.
In a series of experiments published in , the vision scientist Peter Thompson and his colleagues at the University of York in the UK, discovered that the illusion that entasis supposedly counteracts is not there is the first place.
Instead, it appears that one likely reason for entasis was the reinforcement of the columns: a column with entasis is more structurally sound, and provides a greater strength-to-weight ratio, than a non-bulging column. Parva Naturalia. Aristotle, Ross WD Ed , Oxford: Clarendon Press. On the ancient history of the direction of the motion aftereffect. Verstraten FA , Perception 25 10 The origins of entasis: illusion, aesthetics or engineering?
Spat Vis. The views expressed are those of the author s and are not necessarily those of Scientific American. Because there is no third dimension, our brains try to construct space around the figure. People typically see the clockwise variation, which research suggests can be attributed to a tendency to assume a viewpoint from above the figure as well as a tendency to perceive movements of the right as opposed to the left foot.
The oblique lines look as if they are crooked and will diverge. In reality, all of the oblique lines are parallel. Much like the Muller-Lyer and Herring illusions, this optical illusion demonstrates how the background of an image can distort the appearance of straight lines.
First, the angle of the short lines compared to the longer lines creates an impression of depth. One of the lines appears to be nearer to us; the other farther away.
Another possible explanation is that the brain attempts to increase the angles between the long and short lines. This results in distortion as the brain tries to bend the lines away and towards each other. Interestingly, if the color of the lines is switched to green and the background to red, the effect completely disappears as long as the two colors are of equal brightness.
In the Ames room illusion, two people standing in a room appear to be of dramatically different sizes, even though they are the same size. The image above was captured by a visitor to the "Ames room" in the Villette science museum in Paris, France and uploaded to Flickr, a photo-sharing website. In the room, the individual on the left appears to be very tall, while the person on the right looks very small.
In reality, both people are of approximately the same height and size. The effect works by utilizing a distorted room to create the illusion of a dramatic disparity in size.
While the room appears square-shaped from the viewer's perspective, it is actually has a trapezoidal shape. The woman on the right hand side of the image above is actually standing in a corner that is much further away than the woman on the left.
The illusion leads the viewer to believe that the two individuals are standing in the same depth of field when in reality the subject is standing much closer. The effect can be observed in a number of films, including The Lord of the Rings trilogy. Note the early scenes in The Fellowship of the Ring where the effect is prominently used to make Gandalf appear larger than the hobbits.
You can see more examples of Ames rooms in these YouTube videos. In the Ponzo illusion, two identically-sized lines appear to be different sizes when placed over parallel lines that seem to converge as they recede into the distance. In the image above illustrating the Ponzo illusion, the two yellow lines are the exact same size.
Because they are placed over parallel lines that seem to converge in the distance, the top yellow line actually appears to be longer than the bottom one. The Ponzo illusion was first demonstrated in by an Italian psychologist named Mario Ponzo.
The reason the top horizontal line looks longer is that we interpret the scene using a linear perspective. Since the vertical parallel lines seem to grow closer as they move further away, we interpret the top line as being further off in the distance. An object in the distance would need to be longer in order for it to appear the same size as a near object, so the top "far" line is seen as being longer than the bottom "near" line, even though they are the same size.
The Kanizsa Triangle is an optical illusion in which a triangle is perceived even though it is not actually there. The Kanizsa Triangle illusion was first described in by an Italian psychologist named Gaetano Kanizsa. In the illusion, a white equilateral triangle can be seen in the image even though there is not actually a triangle there. The effect is caused by illusory or subject contours. Gestalt psychologists use this illusion to describe the law of closure , one of the gestalt laws of perceptual organization.
According to this principle, objects that are grouped together tend to be seen as being part of a whole. We tend to ignore gaps and perceive the contour lines in order to make the image appear as a cohesive whole. Ever wonder what your personality type means? Sign up to find out more in our Healthy Mind newsletter.
Glover EM, Lauzon O. Using a contrast illusion to teach principles of neural processing. J Undergrad Neurosci Educ. One of the earliest applications of optical illusions was found in Greek rooftops. On temples, roofs were built at a slant, yet observers believed that the rooftops were curved. The optical illusion that the roofs were bowed in baffled many of the Greeks.
Understanding such illusions became a fascination of many philosophers. Some argued that our eyes play tricks on us, yet others decided it had more to do with the mind than the senses. Instead, he thought that our senses betrayed us when viewing optical illusions. Another Greek philosopher, Protagoras, thought the exact opposite. Instead, he thought that optical illusions were dependant on the environment in which they were viewed rather than our senses.
The crossroads at which these two philosophers found themselves became a massive, centuries-long conversation between philosophers, scientists, and psychologists. The next person to try to tackle the theory was Aristotle.
Aristotle, another Greek philosopher from around B. He thought that Protagoras made a great point about our senses: we rely on them for nearly every aspect of assessing reality. Therefore, it was hard to blame the distortions of reality on our five senses.
Distortions such as thinking that a tall building is swaying or seeing water on a road as a result of heat waves are examples of sensory illusions. Another famed Greek philosopher, Plato, pitched in his two cents about the matter. He thought that our minds and our eyes worked together to establish the world, including optical illusions. However, research on the nature of optical illusions has remained pertinent and fascinating throughout history.
When it came to early, intensive studies of optical illusions, two of the most dedicated researchers were Johannes Mueller and J. The 19th-century duo of psychologists took a fascination in understanding the way that people discerned optical illusions.
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