Donald Olding Hebb

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Donald Olding Hebb (July 22, 1904August 20, 1985) was a psychologist who was influential in the area of neuropsychology, where he sought to understand how the function of neurons contributed to psychological processes such as learning. He has been described as the father of neuropsychology and neural networks.


[edit] Life

Donald Hebb was born in Chester, Nova Scotia, the oldest of four children of Arthur M. and M. Clara (Olding) Hebb, and lived there until the age of 16, when his parents moved to Dartmouth, Nova Scotia.

Donald's parents were both physicians. Donald's mother was heavily influenced by the ideas of Maria Montessori and home schooled him until the age of 8. He performed so well in elementary school that he was promoted to the 7th grade at 10 years old. Although his rebellious attitude and disrespect for authority eventually resulted in failing the 11th grade, he still managed to go to graduate school.

The older of Donald's younger brothers, Andrew, obtained a law degree but went on to a career in journalism and then the insurance business. Donald's other younger brother, Peter, went on to become a physician like his parents. And his sister, Catherine, eventually became a prominent physiologist. But Donald, early in life, had no aspirations for psychology or the medical field, he wanted to be a writer. He entered Dalhousie University aiming to become a novelist. He wasn't an exceptional student (his best subjects were math and science) but he graduated with a Bachelor of Arts degree in 1925. Afterwards, he became a teacher, teaching at his old school in Chester. And, later, a farmer in Alberta. He then traveled around as a laborer in Quebec. During his travels he encountered the works of Sigmund Freud (which he regarded as "not too rigorous"), William James, and James Watson which made him consider joining the field of psychology.

At the age of 23, he decided to enter the field of psychology. He asked William Dunlop Tait, the chairman of the pychology department at McGill University (a post Hebb would one day hold) what he'd have to do to get in and was given a reading list and told to come back in a year's time. During this year of study, he went back to teaching.

In 1928, he became a part-time graduate student at McGill University. But, at the same time, he was appointed headmaster of a troubled school in the suburbs of Montreal. He worked with two colleagues from the university, Kellogg and Clarke, to improve the situation. He took a more innovative approach to education, for example assigning more interesting schoolwork and sending anyone misbehaving outside (making schoolwork into a privilege).

In 1931, Hebb became bedridden due to tuberculosis in his hip. He used the time to read Charles Scott Sherrington's The Integrative Action of the Nervous System and Ivan Pavlov's Conditioned Reflexes. His master's thesis, written later that year, titled Conditioned and Unconditioned Reflexes and Inhibition, tried to show that skeletal reflexes were due to cellular learning. This he later dismissed as "nonesense, but no immediate disproof was available at the time". And yet, one of the men who later approved the thesis, Boris Babkin, had worked with Pavlov himself. At the very least, the thesis demonstrated the start of a thought process that would later lead to the Hebb synapse. Hebb passed cum laude. Babkin arranged for Hebb 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 contained many ideas that would later 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. His work at the Montreal school was going badly. In his words, it was "defeated by the rigidity of the curriculum in Quebec's protestant schools". The focus of study at McGill was more in the direction of education and intelligence, and Hebb was now more interested in physiological psychology and was critical of the methodology of the expirements there.

He decided to leave Montreal and wrote to Robert Yerkes at Yale where he was offered a position to study for a PhD. Babkin, however, convinced Hebb to go 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. Here, he had to change his thesis. At Harvard, he did his thesis on the effects of early visual deprivation upon size and brightness perception in a rat. That is, he raised rats in the dark and some in the light and compared their brains. In 1936, he got his PhD from Harvard.

For the duration of the next year, he worked as a research assistant to Lashly and as a teaching assistant in introductory psychology for Edwin G. Boring at Radcliffe College. His Harvard thesis was soon published and he finished the thesis he started at University of Chicago.

In 1937, Hebb married his second wife, Elizabeth. That same year, on a tip from his sister Catherine (herself a PhD student with Babkin at McGill University), he applied to work with Wilder Penfield at the Montreal Neurological Institute. Here he researched the effect of brain surgery and injury on human brain function. He saw that the brain of a child could regain partial or full function when a portion of it is removed, but the similar damage in an adult could be far more 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.

He also became critical of the Stanford-Binet and Wechsler intelligence tests for use 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. Together with N.W. Morton, 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 their frontal lobes removed in order to treat their epilepsy, he noted "a striking post-operative improvement in personality and intellectual capacity". From these sorts of results, he started to believe that the frontal lobes were instrumental in learning only early on in life.

In 1939, he was appointed to a teaching position at Queen's University. In order to test his theory of the changing role of the frontal lobes with age, he designed a variable path maze for rats with Kenneth Williams called the Hebb-Williams maze. A method for testing animal intelligence later used in countless studies. He used the maze to test the intelligence of rats blinded at different developmental stages, showing that "there is a lasting effect of infant experience on the problem-solving ability of the adult rat." This became one of the main principles of developmental psychology, later helping the founding of Head Start programs.

In 1942, he moved to Orange Park, Florida to once again work with Karl Lashley who had replaced Yerkes as the Director of the Yerkes Laboratories of Primate Biology at the Yerkes National Primate Research Center. Here, studying primate behaviour, Hebb developed emotional tests for chimpanzees. Although, the experiment were somewhat unsuccessful as chimpanzees turned out to be hard to teach. During the course of the work there, Hebb wrote The Organization of Behavior: A Neuropsychological Theory, his ground-breaking book which set forth the theory that the only way to explain behaviour was in terms of brain function.

Afterwards, he returned to McGill University to become a professor of psychology in 1947 and was made chairman of the department in 1948. Here, he once again worked with Penfield, but this time through his students, which included Mortimer Mishkin, Haldor Enger Rosvold, and Brenda Milner, all of whom extended his earlier work with Penfield on the human brain.

Hebb remained at McGill until retirement in 1972. Afterwards, in 1976, he returned to Dalhousie University as professor emeritus of psychology.

Hebb was a member of the American Psychological Association (APA) and was its president in 1960. He won the APA Distinguished Scientifict Contribution Award in 1961.

Donald Hebb died in 1985, two years after his wife, in Nova Scotia. He Was survived by two daughters, Mary Ellen Hebb and Jane Hebb Paul.

The Donald O. Hebb Award, named in his honor, is awarded to distinguished Canadian scientists.

[edit] Work

[edit] The Organization of Behavior (1949)

This work is considered Hebb's most important. 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 for a long time could not be connected properly. That is, 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, were based on stimulus and response. That is, a theory 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 travel one way to the brain. It could not explain all the extra processing that adds to the input signals of human senses. And perhaps this was based on the fact that neurons themselves transmit in only one direction. But connections between various neurons are not necessarily one-way.

In 1929, Hans Berger discovered that the mind exhibits continuous electrical activity and cast doubt on the Pavlovian model of perception and response because, now, there appeared to be something going on in the brain even without much stimulus.

At the same time, there were many mysteries. For example, if there was a method for the brain to recognize a circle, how does it recognize circles of various sizes or imperfect roundness? To accommodate every single possible circle that could exist, the brain would need a far greater capacity than it has.

Another theory, the Gestalt theory, stated that signals to the brain established a sort of field. The form of this field only depended on the pattern of the inputs, but it still could not explain how this 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 made it into the mind.

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 did not advance much since the development of the older theories on the operation of the brain, he was still able to piece together a theory that got a lot of the important functions of the brain right.

His theory became known as Hebbian theory and the models which follow this theory are said to exhibit Hebbian learning. This method of learning is best expressed by this quote from the book:

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

This is more often paraphrased as "Neurons that fire together wire together."

The combination of neurons which could be grouped together as one processing unit, Hebb referred to as "cell-assemblies". And their combination of connections made up the ever-changing algorithm which dictated the brain's response to stimuli.

Not only did Hebb's model for the working of the mind influence how psychologists understood the processing of stimuli within the mind, but it also opened up the way for the creation of computational machines that mimicked the biological processes of a living nervous system. And while the method of signal transmission in a nervous system was later found to be due to a complex interaction of chemicals, modern artificial neural networks are still based on the transmission of signals via electrical impulses that Hebbian theory was first designed around.

[edit] Hebb as an educator

Throughout his life Hebb enjoyed and was very successful as a teacher. Both in his early years as a 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 which were then his students.

As a professor at McGill, he believed that you could not teach motivation. The only thing you could do was create the conditions necessary for students to study and do research. You could train them to write, help them choose a problem to study, and even help keep them undistracted, but the motivation and passion for research and study had to come from the student. 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 towards psychology and the way it is taught made McGill University a prominent center of psychological study.

Hebb also came up with the A/S ratio, a value that measures the brain complexity of an organism.

[edit] Known Students

[edit] References

de:Donald O. Hebb fr:Donald Hebb ja:ドナルド・ヘッブ pt:Donald Olding Hebb

Donald Olding Hebb

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