Donald O. Hebb
Donald Olding Hebb (July 22, 1904 – August 20, 1985) was a prominent Canadian psychologist. His seminal book The Organization of Behavior, published in 1949, established Hebb's position in psychology, and led to him being described as the father of neuropsychology, although that title might also belong to Alexander Luria, and of neural networks.
Hebb's interest lay in learning and how information is retained in memory. He sought to understand the function of the brain and its relationship to the activities of the mind. His research involved studies of brain damage as well as sensory deprivation. Putting together his studies of the biological functions of the brain with his work on behavior, Hebb proposed a theory of how brain functions underlie the higher functions of the mind. His proposal of "cell assemblies" as the foundation of memory "engrams" not only addressed the mind-body problem, but also laid the foundation for the development of artificial neural networks and the construction of computational devices that mimic the learning of living systems. Hebb's work has had wide-ranging implications for the study of learning, memory, and brain functions.
His contribution to human knowledge is significant, not only in the theory and its applications, but also in the approach to research that he held and taught his students, namely that even when a theory is wrong (as he often thought his own were) if it was testable it had value and would lead to better understanding. The key to this view is humility, the willingness to put aside a theory once it is proven wrong by experimental data. With such an attitude, the scientific method surely advances knowledge in a positive direction.
Donald Olding Hebb was born in Chester, Nova Scotia, Canada, on July 22, 1904. Donald was the oldest of four children of Arthur and Clara (Olding) Hebb, both physicians. He lived in Chester until the age of 16, when his parents moved to Dartmouth, also in Nova Scotia.
Donald's mother was heavily influenced by the ideas of Maria Montessori, and she home schooled him until the age of eight. He performed well in elementary school, but his rebellious attitude and disrespect for authority led to problems in high school. However, he was able to graduate.
The older of Donald's younger brothers, Andrew, obtained a law degree but went on to a career in journalism and then insurance. Donald's youngest brother, Peter, became a physician like his parents. And his sister, Catherine, eventually became a prominent physiologist. Donald, early in life, had no aspirations toward psychology or the medical field; rather, he wanted to be a writer.
Donald Hebb entered Dalhousie University aiming to become a novelist. He was not an exceptional student but he graduated with a Bachelor of Arts degree in 1925. After working for a number of years as a high school teacher and elementary school principal, Hebb turned to graduate study in psychology at McGill University.
He studied Charles Scott Sherrington's The Integrative Action of the Nervous System and Ivan Pavlov's Conditioned Reflexes, and one of his faculty advisers was Boris Babkin, who had worked with Pavlov. Hebb's master's thesis, entitled Conditioned and Unconditioned Reflexes and Inhibition, tried to show that skeletal reflexes were due to cellular learning. This he later dismissed as nonsense.
Hebb received his M.A. in psychology from McGill University, in 1932. Babkin arranged for him to do research on conditioning with Leonid Andreyev, another former member of Pavlov's laboratory. Between 1933 and 1934, Hebb wrote a booklet titled Scientific Method in Psychology: A Theory of Epistemology Based on Objective Psychology. It was never published, but it contained many ideas that would become part of his later work.
By the beginning of 1934, Hebb's life was in a slump. His wife had died, following a car accident, on his twenty-ninth birthday (July 22, 1933). His work at the Montreal school was going badly. The focus of study at McGill was more in the direction of education and intelligence, and Hebb was now more interested in physiological psychology.
In 1934, Hebb decided to leave Montreal and wrote to Robert Yerkes at Yale University where he was offered a position to study for a Ph.D. in psychology. Babkin, however, convinced Hebb to study with Karl Lashley instead. In July 1934, Hebb was accepted to study under Karl Lashley at the University of Chicago. His thesis was titled The Problem of Spatial Orientation and Place Learning. Hebb, along with two other students, followed Lashley to Harvard University in September, 1935. There, he had to change his thesis. At Harvard, he researched the effects of early visual deprivation upon size and brightness perception in rats, comparing the brains of rats raised in the dark with those raised in the light. He was awarded his Ph.D. in 1936. The next year, he worked as a research assistant to Lashley and as a teaching assistant in introductory psychology for Edwin G. Boring at Radcliffe College.
In 1937, Hebb married his second wife, Elizabeth Nichols Donovan. That same year, on a tip from his sister Catherine (herself a Ph.D. student with Babkin at McGill University), he applied to work with Wilder Penfield at the Montreal Neurological Institute. There he researched the effects of brain surgery and injury on human brain function.
In 1942, Hebb moved to Orange Park, Florida to once again work with Lashley, who had replaced Yerkes as the director of the Yerkes Laboratories of Primate Biology at the Yerkes National Primate Research Center. There, studying primate behavior, Hebb developed emotional tests for chimpanzees. The experiments were somewhat unsuccessful, however, because chimpanzees turned out to be hard to teach. During the course of his work there, Hebb wrote The Organization of Behavior: A Neuropsychological Theory, his ground-breaking book that set forth the theory that the way to explain behavior was in terms of brain function.
Hebb returned to McGill University to become a professor of psychology in 1947 and was made chairman of the department in 1948. There he once again worked with Penfield, but this time through his students, who included Mortimer Mishkin, Haldor Enger Rosvold, and Brenda Milner, all of whom extended his earlier work with Penfield on the human brain.
Hebb was a member of the American Psychological Association (APA) and served as its president in 1960, the first non-US citizen to hold this position. He won the APA Distinguished Scientific Contribution Award in 1961.
Hebb stayed as professor at McGill until his retirement in 1972. He remained there after retirement as an emeritus professor, conducting a seminar course required of all department graduate students. Finally, in 1980, he returned to Dalhousie University as professor emeritus of psychology.
Donald Hebb died in Nova Scotia on August 20, 1985, two years after his third wife. He was survived by two daughters (both by his second marriage), Mary Ellen Hebb and Jane Hebb Paul. The Donald O. Hebb Award, named in his honor, is awarded to distinguished Canadian scientists.
While working with Wilder Penfield at the Montreal Neurological Institute he saw that the brain of a child could regain partial or full function when a portion of it is removed but that similar damage in an adult could be far more damaging, even catastrophic. From this, he deduced the prominent role that external stimulation played in the thought processes of adults. In fact, the lack of this stimulation, he showed, caused diminished function and sometimes hallucinations.
At that time Hebb also became critical of the Stanford-Binet and Wechsler intelligence tests when used with brain surgery patients. These tests were designed to measure overall intelligence, whereas Hebb believed tests should be designed to measure more specific effects that surgery could have had on the patient. To achieve this, he created the Adult Comprehension Test and the Picture Anomaly Test.
Putting the Picture Anomaly Test to use, he provided the first indication that the right temporal lobe was involved in visual recognition. He also showed that removal of large parts of the frontal lobe had little effect on intelligence. In fact, in one adult patient, who had a large portion of his frontal lobes removed in order to treat his epilepsy, he noted "a striking post-operative improvement in personality and intellectual capacity" (Hebb and Penfield 1940). From these sorts of results, he started to believe that the frontal lobes were instrumental in learning only early in life.
In order to test his theory of the changing role of the frontal lobes with age, he designed a variable path maze for rats. Known as the Hebb-Williams maze, this became a method for measuring spatial and working memory of rats later used in countless studies of animal intelligence. Hebb used the maze to test the intelligence of rats blinded at different developmental stages, concluding that "there is a lasting effect of infant experience on the problem-solving ability of the adult rat" (Brown and Milner 2003). This became one of the main principles of developmental psychology, later helping those arguing the importance of the proposed Head Start programs for preschool children in economically poor neighborhoods.
Hebb's name has often been invoked in discussions of the involvement of psychological researchers in interrogation techniques, including the use of sensory deprivation, because of his research into this field. Speaking at a Harvard symposium on sensory deprivation in 1958, Hebb is quoted as remarking:
The work that we have done at McGill University began, actually, with the problem of brainwashing. We were not permitted to say so in the first publishing.... The chief impetus, of course, was the dismay at the kind of “confessions” being produced at the Russian Communist trials. “Brainwashing” was a term that came a little later, applied to Chinese procedures. We did not know what the Russian procedures were, but it seemed that they were producing some peculiar changes of attitude. How? One possible factor was perceptual isolation and we concentrated on that (Solomon et al 1961).
The Organization of Behavior
The Organization of Behavior (1949) is considered Hebb's most important book. A combination of his years of work in brain surgery mixed with his study of human behavior, it finally brought together the two realms of human perception. That is, it connected the biological function of the brain as an organ together with the higher function of the mind.
There were many theories on how the brain and the mind were connected. Pavlovian theories, for example, involved the connection between stimulus and response, based on the belief that a path existed from sensory organs to the mind, which then made a response. The problem with the theory was that it was assumed that signals traveled one way to the brain, just as neurons themselves transmit in only one direction. However, while individual neurons transmit in only one direction, connections between various neurons are much more complex. As a result, the simple Pavlovian model could not explain all the extra processing that adds to the input signals from human senses.
Another theory, the Gestalt theory, stated that signals to the brain established a sort of "field," the form of which depended on the pattern of the inputs. However, this theory could not explain how such a field was understood by the mind.
The Behaviorist theories at the time did well at explaining how the processing of patterns happened. However, they could not account for how these patterns entered into the mind.
Donald Hebb combined up-to-date data about behavior and the mind into a single theory. And, while the understanding of the anatomy of the brain had not advanced much since the development of the older theories on the operation of the brain, he was still able to piece together a theory that correctly understood many of the important functions of the brain. This account of learning is best expressed in Hebb's words:
When an axon of cell A is near enough to excite cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased (Hebb 1949).
The theory is often summarized as "cells that fire together, wire together," although this is an oversimplification of the nervous system not to be taken literally, as well as not accurately representing Hebb's original statement on changes in cell connectivity strength. The theory is commonly evoked to explain some types of associative learning in which simultaneous activation of cells leads to pronounced increases in synaptic strength. Such learning is known as Hebbian learning.
Hebbian theory concerns how neurons might connect themselves to become memory "engrams," a hypothetical means by which memory traces are stored as biophysical or biochemical change in the brain (and other neural tissue) in response to external stimuli suggested by Hebb's mentor, Karl Lashley. Hebb's theories on the form and function of cell assemblies is described as follows:
The general idea is an old one, that any two cells or systems of cells that are repeatedly active at the same time will tend to become 'associated', so that activity in one facilitates activity in the other (Hebb 1949, 7).
When one cell repeatedly assists in firing another, the axon of the first cell develops synaptic knobs (or enlarges them if they already exist) in contact with the soma of the second cell (Hebb 1949, 63).
Not only did Hebb's model for the working of the mind influence how psychologists understood the processing of stimuli within the mind but also it opened up the way for the creation of computational machines that mimicked the biological processes of a living nervous system. And while the dominant form of synaptic transmission in the nervous system was later found to be chemical, modern artificial neural networks are still based on the transmission of signals via electrical impulses around which Hebbian theory was first designed.
As an educator
Throughout his life, Donald Hebb (or D.O. as his colleagues and students called him) enjoyed teaching. Both in his early years as a high school teacher and a headmaster in a Montreal school and in his later years at McGill University, he proved to be a very effective educator and a great influence on the scientific minds of his students. Hebb's most prominent students include Donald Forgays, Stevan Harnad, Woodburn Heron, Bernard Hymovitch, W. Jake Jacobs, Helen Mahut, Ronald Melzack, Brenda Milner, Peter Milner, Mortimer Mishkin, Aryeh Routtenberg, Seth Sharpless, and Case Vanderwolf.
As a professor at McGill, Hebb believed that one could not teach motivation, but only create the conditions necessary for students under which to do their study and research. One could train them to write, help them choose a problem to study, and even help keep them from being distracted, but the motivation and passion for research and study had to come from the students themselves. He believed that students should be evaluated on their ability to think and create rather than their ability to memorize and reprocess older ideas.
Hebb believed in a very objective study of the human mind, more as a study of a biological science. This attitude toward psychology and the way it is taught made McGill University a prominent center of psychological research.
The frequency of citation to Hebb's work has increased markedly over the years (Martinez and Glickman 1994). This reflected in part the transition from stimulus-response learning theories to more cognitively oriented positions anticipated in Hebb's writings. The bulk of later citations refer to Hebb's speculative postulate regarding the conditions surrounding permanent synaptic change in the nervous system. For many contemporary neuroscientists, Hebb's fame roots on a prescient hypothesis that was not testable in his time but now generates a great deal of research.
Given the necessarily tentative nature of psychological theorizing in the mid-twentieth century, Hebb argued that the best justification for a psychological theory was the production of data that endured long after the details of the theory had fallen by the wayside:
For Hebb, the business of scientific psychology was to make inferences about the unobservable physical substrates of behavior, thinking, personality and emotion. Such inferences were risky (unlike behaviorism's reinforcement schedules), in that they might be very wrong; but as long as they suggested testable predictions and successfully guided research, they were leading toward the truth about the mind. ... 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. There is the room—indeed the need—in Hebb's cognitive psychobiology for studying all of these (Harnad 1985).
Hebb's pioneered a theory of how the mind and brain could actually work together, taking on the mind-body problem that has been an issue for philosophers from the beginning. As his former student, Stevan Harnad, noted:
Hebb reminded us of the problem anew, first through suggestive accounts of his work with Penfield on the localization of memories in the brain, and then from the viewpoint of his own specific hypothesis that thoughts could actually be the activity of reverberating circuits of neurons called "cell-assemblies." I don't think his idea had its full impact on me at the moment he described it. Rather, it was after the lecture, as I thought about it, and thought that my thoughts may well consist of those physical things I was thinking about, that I realized what a radically different world view such a theory represented, and that it all had a ring of reality to it that made the Freudian notions I had been flirting with sound like silly fairy tales. ... Then, almost before the revelation his hypothesis represented had had a chance to take effect, Hebb took it back, informing us that his theory was almost certainly wrong. What followed was his second revelation: That a theory need not be right in order to be informative and to guide us in the right direction. And the cell assembly theory (together with other ideas in Hebb's epochal 1949 monograph, The Organization of Behaviour) had indeed inspired an enormous wealth of research findings, from the effects of sensory enrichment and deprivation to electrical and chemical pleasure centers in the brain to theoretical modeling of neural networks (Harnad 1985).
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