psychology, science or study of the thought processes and behavior of humans and other animals in their interaction with the environment. Psychologists study processes of sense perception, thinking, learning, cognition, emotions and motivations, personality, abnormal behavior, interactions between individuals, and interactions with the environment. The field is closely allied with such disciplines as anthropology and sociology in its concerns with social and environmental influences on behavior; physics in its treatment of vision, hearing, and touch; and biology in the study of the physiological basis of behavior. In its earliest speculative period, psychological study was chiefly embodied in philosophical and theological discussions of the soul.

Development of Modern Psychology

The De anima of Aristotle is considered the first monument of psychology as such, centered around the belief that the heart was the basis for mental activity. The foundations of modern psychology were laid by 17th-century philosopher Thomas Hobbes, who argued that scientific causes could be established for every sort of phenomenon through deductive reasoning. The mind-body theories of Rene Descartes, Baruch Spinoza, and G. W. Leibniz were equally crucial in the development of modern psychology, where the human mind's relation to the body and its actions have been significant topics of debate.

In England the empirical method employed in modern psychological study originated in the work of John Locke, George Berkeley, Thomas Reid, and David Hume. David Hartley, James Mill, John Stuart Mill, and Alexander Bain stressed the relation of physiology to psychology, an important development in the scientific techniques of modern psychology. Important contributions were made in the physiological understanding of human psychology by French philosopher Condillac, F. J. Gall, the German founder of phrenology, and French surgeon Paul Broca, who localized speech centers in the brain.

In the 19th cent., the laboratory work of Ernst Heinrich Weber, Gustave Fechner, Wilhelm Wundt, Hermann von Helmholtz, and Edward Titchener helped to establish psychology as a scientific discipline—both through the use of the scientific method of research, and in the belief that mental processes could be quantified with careful research techniques. The principle of evolution, stemming from Charles Darwin's theory of natural selection, gave rise to what became known as dynamic psychology. The new approach, presented by American psychologist William James in his Principles of Psychology (1890), looked at consciousness as an evolutionary process.

Out of the new orientation in psychology grew the clinical experiments in hysteria and hypnotism carried on by J. M. Charcot and Pierre Janet in France. Sigmund Freud, in his influential theory of the unconscious, gave a new direction to psychology and laid the groundwork for the psychoanalytic model. Freudian theory took psychology into such fields as education, anthropology, and medicine, and Freudian research methods became the foundations of clinical psychology.

The behaviorism of American psychologist John B. Watson was highly influential in the 1920s and 30s, with its suggestion that psychology should concern itself solely with sensory stimuli and behavioral reaction. Behaviorism has been important in modern psychology, particularly through the work of B. F. Skinner since the 1930s.

Equally important was the development of Gestalt psychology by German psychologists Kurt Koffka, Wolfgang Köhler, and Max Wertheimer. Gestalt theory contended that the task of psychology was to study human thought and behavior as a whole, rather than breaking it down into isolated instances of stimulus and response.

Another influential school of psychology was developed in the 1950s and 60s by Abraham Maslow and Carl Rogers. Their humanistic theory asserts that people make rational, conscious decisions regarding their lives, and optimistically suggests that individuals tend to reach toward their greatest potential.

Modern Psychology

Modern psychology is divided into several subdisciplines, each based on differing models of behavior and mental processes. Psychologists work in a number of different settings, including universities and colleges, primary and secondary schools, government agencies, private industry, hospitals, clinics, and private practices. Recent years have seen a rise in the significance of applied psychology—as can be seen from the areas contemporary psychologists concern themselves with—with an attendant decline in the importance of psychology in academia. In the United States, clinical psychology has become a significant focus of the discipline, largely separate from psychological research. Clinical psychologists are responsible for the diagnosis and treatment of various psychological problems.

Biological models of behavior have become increasingly prominent in psychological theory, particularly with the development of various tools—such as the positron emission tomography (PET) scan—for mapping the brain. The field of neuropsychology, which studies the brain and the connected nervous system, has been an outgrowth of this contemporary focus on biological explanations of human thought and behavior. Cognitive models, derived from the Gestalt school of psychology, focus on the various thinking processes which mediate between stimuli and responses.

Educational psychology, derived from the 18th and 19th cent. educational reforms of Friedrich W. Froebel, Johann Pestalozzi, and their follower Johann Herbart, was later expanded by G. Stanley Hall and by E. L. Thorndike. It is concerned with the development of improved methods of teaching and learning.

Social psychology, developed by British psychologists William McDougall and Havelock Ellis, studies the effects of various social environments on the individual. Some other branches of the field include developmental psychology, which studies the changes in thought and behavior through the course of life; experimental psychology, which is the laboratory research involved in the understanding of the mind; and personality psychology, which deals specifically with individual personality and the processes by which it is formed.

In recent years a number of new fields of psychology have emerged. Industrial/organizational psychology, emerging from social psychology, focuses on the workplace and considers such topics as job satisfaction, leadership, and productivity. Health psychology examines how psychological factors contribute to pathology, and demonstrates how psychology can contribute to recovery and illness prevention for such somatic disorders as heart disease, cancer, and diabetes. In environmental psychology, research focuses on how individuals react to their physical environments, and suggests improvements which may be beneficial to psychological health. Other new areas of psychology include counseling psychology, school psychology, forensic psychology, and community psychology.

engineering psychology: see ergonomics.

cognitive psychology, school of psychology that examines internal mental processes such as problem solving, memory, and language. It had its foundations in the Gestalt psychology of Max Wertheimer, Wolfgang Köhler, and Kurt Koffka, and in the work of Jean Piaget, who studied intellectual development in children. Cognitive psychologists are interested in how people understand, diagnose, and solve problems, concerning themselves with the mental processes which mediate between stimulus and response. Cognitive theory contends that solutions to problems take the form of algorithms—rules that are not necessarily understood but promise a solution, or heuristics—rules that are understood but that do not always guarantee solutions. In other instances, solutions may be found through insight, a sudden awareness of relationships. Cognitive psychologists have tried to reach a greater understanding of human memory (see memory) and language. In recent years, cognitive psychology has become associated with information processing, which examines artificial intelligence in computers to find out whether they are capable of problem solving in ways similar to humans. Information processing theory studies the parallels between the human brain and the computer, in the ways that both can receive, process, store, and retrieve information.

Branch of psychology concerned with the personality, attitudes, motivations, and behaviour of the individual or group in the context of social interaction. The field emerged in the U.S. in the 1920s. Topics include the attribution of social status based on perceptual cues, the influence of social factors (such as peers) on a person's attitudes and beliefs, the functioning of small groups and large organizations, and the dynamics of face-to-face interactions.

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Study of the physiological basis of behaviour. Traditional specializations in the field cover perception, motivation, emotion, learning, memory, cognition, or mental disorders. Also considered are other physical factors that affect the nervous system, including heredity, metabolism, hormones, disease, drug ingestion, and diet. An experimental science, physiological psychology relies heavily on laboratory research and quantitative data.

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or I-O psychology

Application of the concepts and methods of experimental, clinical, and social psychology to the workplace. I-O psychologists are concerned with such matters as personnel evaluation and placement, job analysis, worker-management relations (including morale and job satisfaction), workforce training and development (including leadership training), and productivity improvement. They may work closely with business managers, industrial engineers, and human-resources professionals.

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Twentieth-century movement in psychology, developed largely in reaction against behaviourism and psychoanalysis, that emphasizes the importance of values, intentions, and meaning in the compass of the individual. The concept of the “self” is a central focus for most humanistic psychologists. Architects of the humanistic approach included Abraham H. Maslow, Carl R. Rogers, and Rollo May (1909–94). Types of humanistic therapies have included sensory awareness, encounter groups, existential analysis, Gestalt therapy, logotherapy, and various transpersonal, human-potential, holistic-health, and addiction-recovery schools.

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In psychology, a broad school of thought that originated in the U.S. in the late 19th century and emphasized the total organism in its endeavours to adjust to the environment. Reacting against the school of structuralism led by Edward Bradford Titchener, functionalists such as William James, George Herbert Mead, and John Dewey stressed the importance of empirical, rational thought over an experimental trial-and-error philosophy. The movement concerned itself primarily with the practical applications of research (see applied psychology) and was critical of early forms of behaviourism.

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Branch or type of psychology concerned with employing empirical principles and procedures in the study of psychological phenomena. The experimental psychologist seeks to carry out tests under controlled conditions in order to discover an unknown effect or law, to examine or establish a hypothesis, or to illustrate a known law. The areas of study that rely most heavily on the experimental method include those of sensation and perception, learning and memory, motivation, and physiological psychology. Experimental approaches are also used in child psychology, clinical psychology, educational psychology, and social psychology.

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or human engineering or human factors engineering

Profession of designing machines, tools, and work environments to best accommodate human performance and behaviour. It aims to improve the practicality, efficiency, and safety of a person working with a single machine or device (e.g., using a telephone, driving a car, or operating a computer terminal). Taking the user into consideration has probably always been a part of tool design; for example, the scythe, one of the oldest and most efficient human implements, shows a remarkable degree of ergonomic engineering. Examples of common devices that are poorly designed ergonomically include the snow shovel and the computer or typewriter keyboard.

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Branch of psychology concerned with the learning processes and psychological issues associated with the teaching and training of students. The educational psychologist studies the cognitive development of students and the various factors involved in learning, including aptitude and learning measurement, the creative process, and the motivational forces that influence student-teacher dynamics. Two early leaders in the field were G. Stanley Hall and Edward L. Thorndike. Seealso school psychology.

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Branch of psychology concerned with changes in cognitive, motivational, psychophysiological, and social functioning that occur throughout the human life span. In the late 19th and early 20th centuries, developmental psychologists were concerned primarily with child psychology. In the 1950s they became interested in the relationship between child rearing and adult personality, as well as in examining adolescence in its own right. By the late 20th century they had become interested in all aspects of psychological development and change over the entire life span.

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Study of similarities and differences in behavioral organization among living beings. The discipline pays particular attention to the psychological nature of humans in comparison with other animals. It began to emerge in the late 19th century and grew rapidly in the 20th century, involving experimental studies on human and animal brain function, learning, and motivation. Well-known studies have included those of Ivan Pavlov on conditioning in laboratory dogs, those of Harry Harlow (1905–81) on the effects of social deprivation in monkeys, and those of various researchers on language abilities in apes.

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Branch of psychology concerned with the diagnosis and treatment of mental disorders. Clinical psychologists evaluate patients through interviews, observation, and psychological tests, and they apply current research findings and methodologies in making diagnoses and assigning treatments. Most clinical psychologists hold an academic degree (Ph.D. or Psy.D.) rather than a medical degree (M.D.); they may provide psychotherapy but cannot prescribe medications. Most practictioners work in hospitals or clinics or in private practice, often in tandem with psychiatrists and social workers, treating mentally or physically disabled patients, prison inmates, drug and alcohol abusers, and geriatric patients, among others. Seealso psychiatry; social work.

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Study of the psychological processes of children. The field is sometimes subsumed under developmental psychology. Data are gathered through observation, interviews, tests, and experimental methods. Principal topics include language acquisition and development, motor skills, personality development, and social, emotional, and intellectual growth. The field began to emerge in the late 19th century through the work of German psychophysiologist William Preyer, American psychologist G. Stanley Hall, and others. In the 20th century the psychoanalysts Anna Freud and Melanie Klein devoted themselves to child psychology, but its most influential figure was Jean Piaget, who described the various stages of childhood learning and characterized children's perceptions of themselves and the world at each stage. Seealso school psychology.

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Branch of psychology concerned with solving practical problems of human behaviour by using the findings and methods of psychological science. Intelligence testing, legal problems, industrial efficiency, motivation, and delinquency were among the first areas of application in the early 20th century. World Wars I and II fostered work on vocational testing, teaching methods, evaluation of attitudes and morale, performance under stress, propaganda and psychological warfare, and rehabilitation. The aviation and aerospace industries were important for the development of engineering psychology, the study of human-machine relationships. Other areas include consumer psychology, school psychology, and community psychology. Seealso industrial-organizational psychology; psychometrics.

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Psychoanalytic method of Carl Jung as he distinguished it from that of Sigmund Freud. Jung attached less importance than did Freud to the role of childhood sexual conflicts in the development of neurosis. Moreover, he defined the unconscious to include both the individual's own unconscious and that inherited, partly in the form of archetypes, from his or her ancestors (the “collective unconscious”). He classified people into introvert and extravert types and further distinguished them according to four primary functions of the mind—thinking, feeling, sensation, and intuition—one or more of which predominated in any given person.

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or psychopathology

Branch of psychology. It is concerned with mental and emotional disorders (e.g., neurosis, psychosis, mental deficiency) and with certain incompletely understood normal phenomena (such as dreams and hypnosis). The chief tool used in classifying psychological disorders is the American Psychiatric Assn.'s Diagnostic and Statistical Manual of Mental Disorders 4th edition (DSM-IV).

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