Hebb, Donald Olding

Donald Olding Hebb (1904-1985) was, during his lifetime, an extraordinarily influential figure in the discipline of psychology. His principled opposition to radical BEHAVIORISM and emphasis on understanding what goes on between stimulus and response (perception, LEARNING, thinking) helped clear the way for the cognitive revolution. His view of psychology as a biological science and his neuropsychological cell-assembly proposal rejuvenated interest in physiological psychology. Since his death, Hebb's seminal ideas exert an ever-growing influence on those interested in mind (cognitive science), brain (neuroscience), and how brains implement mind (cognitive neuroscience).

On graduating from Dalhousie University in 1925, Hebb aspired to write novels, but chose instead the more practical field of education and quickly became a school principal. 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 doctorate at Harvard on the effects of early visual deprivation on size and brightness perception in the rat. He accepted Wilder PENFIELD's offer of a fellowship at the Montreal Neurological Institute, where he explored the impact of brain injury and surgery, particularly lesions of the frontal lobes, on human intelligence and behavior. From his observations that removal of large amounts of tissue might have little impact on MEMORY and INTELLIGENCE, Hebb inferred a widely distributed neural substrate. At Queens University, Hebb developed human and animal intelligence tests (including the "Hebb-Williams" maze) and concluded that experience played a much greater role in determining intelligence than was typically assumed (Hebb 1942).

In 1942 Hebb rejoined Lashley, who had become director of the Yerkes Laboratory of Primate Biology. There Hebb explored fear, anger, and other emotional processes in the chimpanzee (cf. EMOTION AND THE ANIMAL BRAIN). Stimulated by the intellectual climate at Yerkes, Hebb began writing a book synthesizing different lines of research into a "general theory of behavior that attempts to bridge the gap between neurophysiology and psychology" (Hebb 1949: vii). Hebb returned to McGill as professor of psychology and in 1948 was appointed chair. 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 the brain mechanisms of behavior, led to many important discoveries, and steered contemporary psychology onto a more fruitful path.

For Hebb "the problem of understanding behavior is the problem of understanding the total action of the nervous system, and vice versa" (1949: xiv), and his advocacy of an interdisciplinary effort to solve this "neuropsychological" problem was his most general theme. When Hebb's book was published physiological psychology was in decline, and there was a growing movement in psychology to reject physiological concepts (Skinner 1938). The Organization of Behavior marked a turning point away from this trend. Metaphors, using nonbiological devices with well-understood properties, figure prominently in the history of attempts to explain behavior and thought. The mental chemistry of the British Associationists, hydraulics of psychotherapy, magnetic fields of Gestalt psychology, and the computer metaphor of information processing psychology were all fruitful to a point, but then limited and misleading. Hebb's appealingly simple alternative was to explain human and animal behavior and thought in terms of the actual device that produces them -- the brain. In The Organization of Behavior, Hebb presented just such a neuropsychological theory.

There were three pivotal postulates: (1) Connections between neurons increase in efficacy in proportion to the degree of correlation between pre- and postsynaptic activity. In neuroscience this corresponds to the "Hebb synapse," the first instances of which were later discovered in LONG-TERM POTENTIATION and kindling, whereas in cognitive science this postulate provides the most basic learning algorithm for adjusting connection weights in artificial NEURAL NETWORK models. (2) Groups of neurons that tend to fire together form a cell-assembly whose activity can persist after the triggering event and serves to represent it. (3) Thinking is the sequential activation of a set of cell-assemblies.

Hebb knew that his theory was speculative, vague, and incomplete. Missing from the model, for example, was neural inhibition (Milner 1957), a concept Hebb later incorporated (1959). But Hebb believed that a class of theory was needed, of which his was merely one specific form -- subject to modification or rejection in the face of new evidence. Hebb's ideas were certainly fruitful in generating new evidence, as whole literatures on the role of early experience in PERCEPTUAL DEVELOPMENT (Hunt 1979), sensory deprivation (Zubek 1969), self stimulation (Olds and Milner 1954), the stopped retinal image (Pritchard, Heron, and Hebb 1960), synaptic modifiability (Goddard 1980), and learning without awareness (McKelvie 1987), were provoked or fostered by them.

When philosophy and physiology converged in the nineteenth century, psychology emerged with the promise of a science of mental life (Boring 1950). By providing a neural implementation of the Associationists' mental chemistry Hebb fulfilled this promise and laid the foundation for neoconnectionism, which seeks to explain cognitive processes in terms of connections between assemblies of real or artificial neurons.

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-- Raymond M. Klein

References

Boring, E. G. (1950). A History of Experimental Psychology. 2nd ed. New York: Appleton-Century-Crofts.

Goddard, G. V. (1980). Component properties of the memory machine: Hebb revisited. In P. W. Jusczyk and R. M. Klein, Eds., The Nature of Thought: Essays in Honor of D. O. Hebb. Hillsdale, NJ: Erlbaum, pp. 231-247.

Hebb, D. O. (1942). The effects of early and late brain injury upon test scores, and the nature of normal adult intelligence. Proceedings of the American Philosophical Society 85:275-292.

Hebb, D. O. (1949). The Organization of Behavior: A Neuropsychological Theory. New York: Wiley.

Hebb, D. O. (1959). A neuropsychological theory. In S. Koch, Ed., Psychology: A Study of a Science, vol. 1. New York: McGraw-Hill.

Hunt, J. M. (1979). Psychological development: early experience. Annual Review of Psychology 30:103-143.

McKelvie, S. (1987). Learning and awareness in the Hebb digits task. Journal of General Psychology 114:75-88.

Milner, P. M. (1957). The cell assembly: Mark II. Psychological Review 64:242-252.

Olds, J., and P. M. Milner. (1954). Positive reinforcement produced by electrical stimulation of the septal area and other regions of the rat brain. Journal of Comparative and Physiological Psychology 47:419-427.

Pritchard, R. M., W. Heron, and D. O. Hebb. (1960). Visual perception approached by the method of stabilized images. Canadian Journal of Psychology 14:67-77.

Skinner, B. F. (1938). The Behavior of Organisms: An Experimental Analysis. New York: Appleton-Century.

Zubek, P. (1969). Sensory Deprivation: 15 Years of Research. New York: Meredith.

Hebb, Donald Olding

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