Infographic 3.3: Perceptual Illusions

The introductory text reads as follows: What we see, hear, taste, touch, smell, and feel may seem very real, but perceptions are not always accurate representations of reality. The brain’s perceptual systems are prone to errors and distortions. Studying illusions, like those shown here, we can detect and better understand the brain’s misinterpretations of visual input. There are four frames on the infographic, each showing an image or illustration and explanation of an illusion. The first is labeled “Moon illusion,” and shows a full moon at the horizon level behind a row of trees. The text reads as follows: Have you ever noticed that the moon can appear much larger when it’s on the horizon versus high in the sky? Don’t let perceptual errors trump logic: you know the moon does not change size! Researchers have yet to agree upon a definitive explanation for this illusion, but many suspect it has something to do with the surrounding environment (Weidner et al., 2014). Seeing the moon along with trees and other objects at different distances may influence our perception of the moon’s size. The frame at the upper right is labeled “Ponzo illusion,” and shows an illustration of a railway track in perspective, getting smaller toward the top of the graphic. There are two horizontal lines of the same length labeled “a.” and “b.” with one close to the bottom and the other close to the top. The text reads as follows: Which of the two red bars is longer? Neither! They are identical. When you see two lines converging in the distance, your brain perceives them as getting farther away. Line A appears farther away. It seems longer because the images of the two lines projected onto the retina are the same size, but we interpret the farther line as being bigger. The Ponzo illusion demonstrates how we judge an object’s size based on its context. The center frame is labeled “Ames Room illusion,” and shows an image and a graphic. In the image, a woman at the right seems to be much taller than a man at the left when seen against what looks like same-sized windows at the back of the room. The graphic shows the structure of the room, where the right corner is much closer to the viewer, and the floor is slanted upward. The window at the right is much smaller than the one at the left. The text reads as follows: Would you believe that the two people in this room (left) are approximately the same height? The woman on the right appears about twice as big, because the room isn’t rectangular! The Ames room is actually trapezoidal (see diagram on the right), but, as the image on the left shows, this is not apparent when it is viewed through a peephole with one eye. The lower frame is labeled, “the Shepard Tables illusion,” and shows illustrations of two tables. The left table labeled “a” appears to be much narrower and longer than the one at the right labeled “b.” The text reads as follows: Look carefully at these two tables. Is one longer than the other? If you compare their measurements with your fingers or a piece of paper, you will see that both the length and width are identical. The brain sees table (a) and thinks the back edge is farther away than table (b), and thus table (a) appears narrower and longer than table (b).