A psychologist is a social scientist who studies behavior and mental processes, generally in a research or clinical setting.
As psychology has grown and changed throughout history, it has been defined in numerous ways. As early as 400 B.C., the ancient Greeks philosophized about the relationship of personality characteristics to physiological traits. Since then, philosophers have proposed theories to explain human behavior. In the late nineteenth century, the emergence of scientific method gave the study of psychology a new focus. In 1879, the first psychological laboratory was opened in Leipzig, Germany by Wilhelm Wundt, and soon afterwards the first experimental studies of memory were published. Wundt was instrumental in establishing psychology as the study of conscious experience, which he viewed as made up of elemental sensations. In addition to the type of psychology practiced by Wundt—which became known as structuralism—other early schools of psychology were functionalism, which led to the development of behaviorism, and Gestalt psychology. The American Psychological Association was founded in 1892 with the goals of encouraging research, enhancing professional competence, and disseminating knowledge about the field.
With the ascendance of the Viennese neurologist Sigmund Freud and his method of psychoanalysis early in the twentieth century, emphasis shifted from conscious experience to unconscious processes investigated by means of free association and other techniques. According to Freud, behavior and mental processes were the result of mostly unconscious struggles within each person between the drive to satisfy basic instincts, such as sex or aggression, and the limits imposed by society. At the same time that Freud's views were gaining popularity in Europe, an American psychology professor, John B. Watson, was pioneering the behavioral approach, which focuses on observing and measuring external behaviors rather than the internal workings of the mind. B. F. Skinner, who spent decades studying the effects of reward and punishment on behavior, helped maintain the predominance of behaviorism in the United States through the 1950s and 1960s. Since the 1970s, many psychologists have been influenced by the cognitive approach, which is concerned with the relationship of mental processes to behavior. Cognitive psychology focuses on how people take in, perceive, and store information, and how they process and act on that information.
Additional psychological perspectives include the neurobiological approach, focusing on relating behavior to internal processes within the brain and nervous system, and the phenomenological approach, which is most concerned with the individual's subjective experience of the world rather than the application of psychological theory to behavior. While all these approaches differ in their explanations of individual behavior, each contributes an important perspective to the overall psychological understanding of the total human being. Most psychologists apply the principles of various approaches in studying and understanding human nature.
Along with several approaches to psychology there are also numerous, overlapping subfields in which these approaches may be applied. Most subfields can be categorized under one of two major areas of psychology referred to as basic and applied psychology. Basic psychology encompasses the subfields concerned with the advancement of psychological theory and research. Experimental psychology employs laboratory experiments to study basic behavioral processes shared by different species, including sensation, perception, learning, memory, communication, and motivation. Physiological psychology is concerned with the ways in which biology shapes behavior and mental processes, and developmental psychology is concerned with behavioral development over the entire life span. Other subfields include social psychology, quantitative psychology, and the psychology of personality.
Applied psychology is the area of psychology concerned with applying psychological research and theory to problems posed by everyday life. It includes clinical psychology, the largest single field in psychology. Clinical psychologists—accounting for 40% of all psychologists—are involved in psychotherapy and psychological testing. Clinical psychologists are trained in research and often work in university or research settings, studying carious aspects of psychology. Like clinical psychologists, counseling psychologists apply psychological principles to diagnose and treat individual emotional and behavioral problems. Other subfields of applied psychology include school psychology, which involves the evaluation and placement of students; educational psychology, which investigates the psychological aspects of the learning process; and industrial and organizational psychology, which study the relationship between people and their jobs. Community psychologists investigate environmental factors that contribute to mental and emotional disorders; health psychologists deal with the psychological aspects of physical illness, investigating the connections between the mind and a person's physical condition; and consumer psychologists study the preferences and buying habits of consumers as well as their reactions to certain advertising.
In response to society's changing needs, new fields of psychology are constantly emerging. One new type of specialization, called environmental psychology, focuses on the relationship between people and their physical surroundings. Its areas of inquiry include such issues as the effects of overcrowding and noise on urban dwellers and the effects of building design. Another relatively new specialty is forensic psychology, involving the application of psychology to law enforcement and the judicial system. Forensic psychologists may help create personality profiles of criminals, formulate principles for jury selection, or study the problems involved in eyewitness testimony. Yet another emerging area is program evaluation, whose practitioners evaluate the effectiveness and cost efficiency of the programs.
Depending on the nature of their work, psychologists may practice in a variety of settings, including colleges and universities, hospitals and community mental health centers, schools, and businesses. A growing number of psychologists work in private practice and may also specialize in multiple subfields. Most psychologists earn a Ph.D. degree in the field, which requires completion of a four-to six-year post-bachelors' degree program offered by a university psychology department. The course of study includes a broad overview of the field, as well as specialization in a particular subfield, and completion of a dissertation and an internship (usually needed only for applied psychology, such as clinical, counseling, and school psychology). Students who intend to practice only applied psychology rather than conduct research have the option of obtaining a Psy.D. degree, which differs in the limited emphasis that is put on research and a dissertation that does not have to be based on an empirical research study.