Neurophysiological Theory of Learning
Biography
Donald Olding Hebb has been called the "Father of Cognitive Psychobiology". Hebb was raised in Chester, Nova Scotia, and graduated from Dalhousie University in 1925. The writings of James, Freud, and Watson stimulated his interest in psychology, and as a part time graduate student at McGill University, Hebb was exposed to Pavlov's program. Unimpressed, Hebb was "softened up for [his] encounter with Kohler's Gestalt Psychology and Lashley's critique of reflexology." Hebb went to work with Lashley, and in 1936 completed his PhD at Harvard on the effects of early visual deprivation upon size and brightness perception in the rat. He joined the faculty at McGill University.
He would later point out that every bit of behavior is jointly determined by heredity and environment, just as the area of a field is jointly determined by its length and its width. His book, "The Organization of Behavior: A Neuropsychological Theory," wielded a kind of magic in the years after its appearance (Hebb, 1949). It attracted many brilliant scientists into psychology, made McGill University a North American mecca for scientists interested in brain mechanisms of behavior, led to many important discoveries, and steered contemporary psychology onto a more fruitful path.
Theory
Hebb described his system as "psuedo-behavioristic". He was preoccupied with explaining higher mental processes such as thinking and perception. These are not usually within the scope of rigid behaviorism. Hebb was inspired by the work of B.F. Skinner, and always stated with complete conviction that he regarded Skinner as the greatest psychologist of the century. Over the course of his career, Hebb moved away from behaviorism and argued that thoughts are processes represented in the head, and that behaviorism, in an over-reaction against introspectionism, was begging the important questions in psychology.
For Hebb, the business of scientific psychology was to make inferences about the unobservable physical substrates of behavior, thinking, personality and emotion. Hebb had learned from behaviorism was that it is unwise scientific practice to ignore anything, be it our brain, our biological heritage, our cognition or our conscious experience. He was a proponent of including study of all of these, and maintained a healthy skeptiism toward all theories, inluding his own. He resisted the position that he, or anyone else, had found the answers.
Hebb was intriged with the question of what occurs between a stimulus (S) and a response (R) when there is a lapse of time between the two. Arousal, the activting effect of a stimulus, is key in Hebb's theory. He believed that thoughts mediated the responses by collaborating with sensory input to determine which of a number of possible responses could be made.
Hebb's epochal 1949 monograph, The Organization of Behavior explained internal processes in neurological terms. He believed that repeated transmissions of neurological impulses between neurons lead to permanent facilitation of future impulses along the same pathway. He envisioned assemblies of neurons which could contain up to thousands of individual cells, as reverbatory loops. He suggested that thoughts could actually be the activity of reverberating circuits of neurons called "cell-assemblies."These were also connected to other similar loops in a hierarchical manner. This facilitative process was a central feature of Hebb's explanations of learning.
Two other key concepts were reactivity, the capacity of an organism to react to external stimuli, and plasticity, the ability of the organism to change its response patterns over time.
Mediation, or thought, consists of activity in a cell assembly or closed pathway. A series of such activities is a "phase sequence". The nature of the mediation (thought) is determined by the specific assemblies that are involved. "Associated assemblies" form as a result of repeated sensory events. Higher processes such as problem solving involve supraordinate phase sequences, which are combinations of cell assemblies or phase sequences.
Hebb regarded motivation and learning as related properties and did not speak of them as different theories.
Learning Theory Bibliography
Harnad, S. (1985)
Hebb, D. O. (1949).
LeFrancois (1972)