1. What you See isn’t what your Brain Gets
You think that as you’re walking around looking at the world, your eyes are sending information to your brain, which processes it and gives you a realistic experience of “what’s out there.” But the truth is that what your brain comes up with isn’t exactly what your eyes are seeing. Your brain is constantly interpreting everything you see. Take a look at Figure 1.1, for example.
FIGURE 1.1 You see triangles, but they are not really there
What do you see? At first you probably see a triangle with a black border in the background and an upside-down white triangle on top of it. Of course, that’s not really what’s there, is it? In reality there are merely lines and partial circles. Your brain creates the shape of an upside-down triangle out of empty space, because that’s what it expects to see. This particular illusion is called a Kanizsa triangle, named for the Italian psychologist Gaetano Kanizsa, who developed it in 1955. Now look at Figure 1.2, which creates a similar illusion with a rectangle.
FIGURE 1.2 An example of a Kanizsa rectangle
The brain creates shortcuts
Your brain creates these shortcuts in order to quickly make sense out of the world around you. Your brain receives millions of sensory inputs every second (the estimate is 40 million), and it’s trying to make sense of all of that input. It uses rules of thumb, based on past experience, to make guesses about what you see. Most of the time that works, but sometimes it causes errors.
You can influence what people see, or think they see, by the use of shapes and colors. Figure 1.3 shows how color can draw attention to one message over another.
FIGURE 1.3 Color and shapes can influence what people see
The eye has 7 million cones that are sensitive to bright light and 125 million rods that are sensitive to low light. The cones are in the fovea (central area of vision), and the rods are less central. So if you’re in low light, you’ll see better if you don’t look right at the area you’re trying to see.
Optical illusions are examples of how the brain misinterprets what the eyes see. For example, in Figure 1.4 the line on the left looks longer than the line on the right, but they’re actually the same length. Named for Franz Müller-Lyer, who created it in 1889, this is one of the oldest optical illusions.
FIGURE 1.4 These lines are actually the same length
Light rays enter the eye through the cornea and lens. The lens focuses an image on the retina. On the retina it is always a two-dimensional representation, even if it is a three-dimensional object. This image is sent to the visual cortex in the brain, and that’s where recognition of patterns takes place—for example, “Oh, I recognize that as a door.” The visual cortex turns the 2D image into a 3D representation.