Imagine you take half a grapefruit out of the refrigerator and dig into it with a spoon. Some juice splashes out of the fruit and hits your nose and mouth. What do your senses tell you? You smell some strong fragrance. You feel something cold on your skin. You taste something sharp on your tongue. So far, your experi- ence consists of raw sensation. Your sensory systems have detected features of the juice.
Sensation is the detection of physical stimuli from the world around us and the sending of that information to the brain. Physical stimuli can be light waves, sound waves, food molecules, odor molecules, temperature changes, or pressure changes on the skin. In sensing the splash of the grapefruit juice, you are sensing food molecules, odor molecules, slight temperature changes, and slight pressure changes.
Perception is the brain’s further processing of sensory information. This processing results in our conscious experience of the world. The essence of perception is interpreting sensation. That is, our perceptual systems (as opposed to our sensory systems) translate sensation into information that is meaningful and useful. In the above example, perception is interpretation of the sensory stimuli of cold droplets, a strong smell, and a sharp taste as qualities of grapefruit.
But even when people experience the exact same sensory input (sensation), they experience that input differently (perception). If you like grapefruit, you might experience this splash as at least partly pleasant. If you dislike grape- fruit—suppose your father has insisted that you eat it—you might experience the splash as totally unpleasant. The Try It Yourself exercise on p. 158 will help you begin to understand the differences between sensation and perception.
Our Senses Detect Physical Stimuli, and Our Brains Process Perception Suppose you are driving, and the traffic signal changes from red to green. Believe it or not, there is actually no red or green color in the signal or in the light you see. Instead, your eyes and brain enable you to see the redness or greenness of the light. Objects in the physical world don’t actually have color. Each object reflects light waves of particular lengths. Our visual systems interpret those waves as different colors.