Psychologists at Work
　　Psychology is the scientific study of behavior and mental processes. The simplicity of this definition is in some ways deceiving, concealing ongoing debates about how broad the scope of psychology should be. Should psychologists limit themselves to the study of outward, observable behavior? Is it possible to study thinking scientifically? Should the field encompass the study of such diverse topics as physical and mental health, perception, dreaming, and motivation? Is it appropriate to focus solely on human behavior, or should the behavior of other species be included?
　　Most psychologists would argue that the field should be receptive to a variety of viewpoints and approaches. Consequently, the phrase behavior and mental processes in the definition of psychology must be understood to mean many things: It encompasses not just what people do but also their thoughts, emotions, perceptions, reasoning processes, memories, and even the biological activities that maintain bodily functioning.
　　Psychologists try to describe, predict, and explain human behavior and mental processes, as well as helping to change and improve the lives of people and the world in which they live. They use scientific methods to find answers that are far more valid and legitimate than those resulting from intuition and speculation, which are often inaccurate (see Figure 1).
　　The Subfields of Psychology: Psychology’s Family Tree
　　As the study of psychology has grown, it has given rise to a number of subfields (described in Figure 2). The subfields of psychology can be likened to an extended family, with assorted nieces and nephews, aunts and uncles, and cousins who, although they may not interact on a day-to-day basis, are related to one another, because they share a common goal: understanding behavior. One way to identify the key subfields is to look at some of the basic questions about behavior that they address.
　　WHAT ARE THE BIOLOGICAL FOUNDATIONS OF BEHAVIOR?
　　In the most fundamental sense, people are biological organisms. Behavioral neuroscience is the subfield of psychology that mainly examines how the brain and the nervous system—but other biological processes as well—determine behavior. Thus, neuroscientists consider how our bodies influence our behavior. For example, they may examine the link between specific sites in the brain and the muscular tremors of people affected by Parkinson’s disease or attempt to determine how our emotions are related to physical sensations. Behavioral neuroscientists might want to know what physiological changes occurred as movie patrons in the theater where Batman was showing realized they were being shot at.
　　HOW DO PEOPLE SENSE, PERCEIVE, LEARN, AND THINK ABOUT THE WORLD?
　　If you have ever wondered why you are susceptible to optical illusions, how your body registers pain, or how to make the most of your study time, an experimental psychologist can answer your questions. Experimental psychology is the branch of psychology that studies the processes of sensing, perceiving, learning, and thinking about the world. (The term experimental psychologist is somewhat misleading: Psychologists in every specialty area use experimental techniques.)
　　Several subspecialties of experimental psychology have become specialties in their own right. One is cognitive psychology , which focuses on higher mental processes, including thinking, memory, reasoning, problem solving, judging, decision making, and language. For example, a cognitive psychologist might be interested in what the survivors of the Batman theater shooting remembered later about their experience.
　　WHAT ARE THE SOURCES OF CHANGE AND STABILITY IN BEHAVIOR ACROSS THE LIFE SPAN?
　　A baby producing her first smile . . . taking his first step . . . saying its first word. These universal milestones in development are also singularly special and unique for each person. Developmental psychology studies how people grow and change from the moment of conception through death. Personality psychology focuses on the consistency in people’s behavior over time and the traits that differentiate one person from another.
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