We will begin with sensation, the physical process by which we use our sense organs (i.e. tongues for taste or noses for smell) to respond to the environmental stimuli around us. Perception, on the other hand, refers to our interpretation of stimuli. It occurs through cognitive processing and enables us to use information in order to change our behavior. While these processes may seem simple, they are just the opposite: large portions of the brain are devoted to the seemingly straightforward processes of seeing and hearing, and entire sensory organs have developed in order to facilitate them. Further, while the brain is constantly using the information it gathers to make decisions, we are entirely unaware of this activity. Unbelievably, studying illusions is one of the easiest ways to learn about how we process stimuli (especially visual stimuli). We will accordingly devote a substantial amount of time to illusions later in this course. In this course, you will not only learn how we use sensation and perception to understand the world around us, but identify the ways in which these processes can fail. We will take a close look at how we use specific behaviors in the presence of certain stimuli by learning about the biology of both the hearing system and the visual system (we will learn, for example, how the visual system measures light, how it sees color and motion, and how it recognizes distinct objects). We will conclude with a discussion of how the other senses (smell, taste, and touch) affect perception.