George Kelly, perhaps the first cognitive theorist and most influential between the 1930s and 1960s, worked as a clinical psychologist and university professor. He developed a fundamental postulate to explain his psychological theory, which is essentially that a person acts in such a way based on his interpretation of past events. Kelly introduced the notion of "psychological space," which is basically a term for the region into which we place and classify elements of our world and surroundings. He also introduced personal construct theory and defined "construct," which is a person's internal or psychological representation of reality and ideas.
The development of cognitive theory influenced other psychologists and important theorists in psychology. For example, behaviorist Edward Tolman introduced the idea of "cognitive maps" and proposed that rats and other organisms create such a cognitive map to figure out their environment. Theories of human and personality development, including those of Piaget and Vygotsky, also emphasize cognitive processes to explain human learning and thinking. Cognitive theories also gave rise to information processing theories, such as those of George Miller, and continue to be one of the dominant forces in the psychology field in the 21st Century.
Cognitive theories underlie many of the treatments used in professional and clinical psychology. Cognitive psychologists attempt to help individuals identify and change negative or destructive patterns in thinking. Many assessment techniques have developed as a way to measure cognitive processes. For example, the Beck Depression Inventory and the Beck Anxiety Inventory can be used to assess severity of depression and levels of anxiety. Other applications of psychology also use cognitive theories, such as industrial/organizational psychology and human factors.
Critics of cognitive theories in psychology contend that these theories largely ignore innate biological processes, such as hormones, in determining the way a person behaves and develops. Others criticize cognitive theories because it may be too difficult to quantify or measure a person's thoughts or cognitive processes. In other words, behaviors cannot be objectively studied using cognitive theories. Cognitive theories have also been criticized as being overly simplistic, explaining human behavior in terms of the way a machine works. This "machine reductionism" criticism argues that humans use not only past experiences when interacting with the environment, but also emotions and other elements of higher thinking as well.