Every behavior that a human or animal performs involves taking in information from the primary senses: vision, hearing, and touch. Many drugs of abuse change this sensory information. Mind-altering drugs can influence the way people perceive time, the way they think and behave, and their moods. Drugs also have an effect on memory. Just as people are always receiving sensory information, they are always learning things in the course of daily life. Imagine all of the sensory information—seeing, hearing, feeling—that a toddler must take in when taking a first, unassisted step. Very quickly children learn not to go near the street, that fire burns, that the fur of a kitten is soft, and that when pushed, the buttons on a remote control turn on a television. Within a few years, a young...