Optical Illusions
The word “illusion” comes from the Latin word illudere, which means “to mock.”
What is an optical illusion? Optical illusions are images or pictures that we perceive
differently than they really are. Put another way, optical illusions occur when our eyes send
information to our brains that tricks us into perceiving something that does not match reality.
Scientists believe optical illusions are possible because our brains are so good at recognizing
patterns and seeing familiar objects. Our brains work quickly to make a whole image from
separate pieces.
What do optical illusions tell us about visual perception? To perceive is to create a figure
or shape that does not necessarily appear as such in the real world but that we can represent
mentally so that we can recognize it under various conditions (for instance, when it is partly
hidden). By studying the way that the brain fills in missing or ambiguous visual information, we
can learn a lot about the way that we perceive the world. Optical illusions provide fertile
ground for such study, because they involve ambiguous images that force the brain to make
decisions that tell us about how we perceive things.
Optical illusions give us a better understanding of how human visual perception works.
They force us to recognize that opposite to what we might think, what we see of the world is
not a simple physical record like a picture. On the contrary, the signals that your eyes receive
from the elements in a scene in front of them are often ambiguous. Your brain is constantly
interpreting these signals to construct an image that makes sense to it. In fact, your brain tries
so hard to make sense of everything that it often finds meaning even where there is none, thus
creating optical illusions.
3 different types of optical illusions: Cognitive, Physiological, and Literal illusions.
Literal Illusions: What is a literal illusion? A literal illusion creates images that are
different from the objects that make them. For example:
Some optical illusions are physiological. Which means that they’re caused by some sort
of physical means in the eyes or the brain.
Distorting illusions use different techniques to make objects of similar size, length or
curvature appear distorted. A famous example of a distorting illusion is the Müller Lyer illusion.
Doesn’t the line in the middle look longer than the ones above and below it? But really,
all three lines are the same length. Paradox illusions occur as a result of pictures or objects that
cannot exist or are physically impossible. Paradox illusions are popular in works of art.
Cognitive Illusions
The way you look at an object can affect how you see it. Sometimes there are
two images in the same picture, but you can only see one at a time so your brain chooses one
(when it deals with too much information).
Cognitive illusions rely on knowledge about the world and are also under
conscious control.
Ambiguous illusions are pictures or objects that offer significant changes in appearance.
Perception will 'switch' between the alternates as they are considered in turn as available data
does not confirm a single view. The Necker cube is a well-known example, the motion parallax
due to movement is being misinterpreted, even in the face of other sensory data. Another
popular is the Rubin vase.
Paradox Illusion: Paradox Illusions are illusions that are three dimensional and
impossible in real life. But seem oddly convincing in two dimensional drawings. These illusions
are often dependent on a cognitive misunderstanding that adjacent ends must join. The
Penrose Stairs is a great example of a Paradox illusion, also known as the “impossible staircase”.
After-image Illusion: An afterimage is a non-specific term that refers to an image
continuing to appear in one's vision after staring at the original image was shown for a certain
period of time. An afterimage may be a normal phenomenon (physiological afterimage) or may
be pathological (palinopsia). Illusory palinopsia may be a pathological exaggeration of
physiological afterimages. Ewald Hering explained how the brain sees afterimages, in terms of
three pairs of primary colors. This opponent process theory states that the human visual system
interprets color information by processing signals from cones and rods in an antagonistic
manner. The opponent color theory suggests that there are three opponent channels: red
versus green, blue versus yellow, and black versus white. Responses to one color of an
opponent channel are antagonistic to those to the other color. Therefore, a green image will
produce a magenta afterimage. The green color fatigues the green photoreceptors, so they
produce a weaker signal. Anything resulting in less green is interpreted as its paired primary
color, which is magenta.