Thorndike, Edward (1874-1949)

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THORNDIKE, EDWARD (1874-1949)

Edward Lee Thorndike was born on August 31, 1874, in Williamsburg, Massachusetts. He died on August 9, 1949, in Montrose, New York. Thorndike proceeded very rapidly through his graduate education. After receiving a B.A. at Wesleyan University in 1895, he transferred to Harvard University, where he received a second B.A. in 1896 and his M.A. the following year. In 1898, Thorndike completed his Ph.D. at Columbia University, where he spent virtually his entire academic career as a professor at Teachers College (1899-1940). While this article will not dwell on Thorndike's achievements in the applied area that came to be called educational psychology, it should be noted that he created that field and developed it during his entire career at Columbia.

Thorndike's experimental studies of learning in monkeys brought him his first position at Teachers College as an instructor in genetic psychology. The dean of Teachers College, James E. Russell, hired Thorndike because he thought those studies to be "a pretty good stepping stone to a study of the nature and behavior of children" (Current Biography, 1941, p. 857). The ingenuity of Thorndike's animal experiments had made a very favorable impression on William James at Harvard, as well as on his major professors at Columbia, each of whom would have strongly endorsed him for the position in Teachers College. Thorndike's contributions to the fledgling science of psychology are of the highest importance and come down to us well into the end of the twentieth century.

The Study of Animal Intelligence

To Thorndike goes the credit for putting what was to become the experimental psychology of animal learning (the study of animal intelligence) on a sound laboratory and theoretical footing. Thorndike's studies (1911), which began around 1896 at Harvard and continued at Columbia University, were much more controlled than those of any of his predecessors. He employed a variety of vertebrate species (fish, chicks, dogs, cats, monkeys) and typically placed them in a problem situation, such as a puzzle box or a maze, from which they had to escape in order to get food and/or join companions. He observed the number of errors or latency to escape across trials and generally published quantitative information on the behavior of his experimental subjects. He attempted to control the life history or extra-experimental experiences of his animals and also kept the problem situation standard.

General Learning Theory

From his experimental observations, Thorndike proposed a general theory of learning that held that the animal learned the association between an act and a situation on the basis of the success of the act in bringing about a "satisfying" state of affairs. He proposed that it is through the Law of Effect that acts that bring about a satisfying state of affairs are gradually "stamped-in" the nervous system and those that lead to an annoying or discomforting state of affairs are gradually "stamped-out." Thorndike believed the animal had to behave actively to learn in the problem situation and that the animal's particular movements in the particular situation are validated or made invalid depending on whether they lead to satisfying or annoying consequences. Learning was thus the gradual association of particular movements in particular situations leading to certain ends. Thorndike believed that the actual connections between nerve cells in the brain underlying situation-response (S-R) associations were strengthened by reward ("satisfaction") and weakened by punishment ("annoyance").

To better appreciate Thorndike's theoretical contribution, it is necessary to briefly recall the history of thought about learning. The dominant theme of the psychological process involved in learning has always been some sort of associationism, so that was not Thorndike's particular contribution. The change that Thorndike injected into the concept of associationism concerned the nature of the association: It was not ideas that animals associated, it was movements (R) in a given situation (S) that led to satisfying consequences. Thorndike spoke of neuronal connections in the brain and hypothesized that the synaptic links between them were gradually made more traversable by use and by satisfactory consequences, whereas disuse or annoying consequences made the neuronal connections underlying other S-R associations less traversable. This was Thorndike's neurological account of trial-and-error learning, later reintroduced and expanded in a significant way by Donald O. Hebb (1949).

The foregoing represents Thorndike's bequest to what became "general behavior (learning) theory" in the field of psychological science in the 1940s. Today, general behavior theory no longer holds such a central place in psychological science.

Contributions to Animal Psychology

Thorndike also made three influential contributions to comparative (animal) psychology. First, by the introduction of the puzzle box and other standard testing situations, and the careful quantification of his observations, he set the comparative psychology of learning on an objective course from which it has rarely deviated. Thorndike also incidentally helped pave the way for the methodological and theoretical Behaviorism of John B. Watson a decade later, but it is clear that a number of other significant intellectual threads were tending in that same direction around (and even before) the turn of the century: Ivan Sechenov's "reflexes of the brain" (1863), Ivan Pavlov's highly quantitative conditioning procedures (Yerkes and Morgulis, 1909), Jacques Loeb's (1912) physicochemical reductionism and his tropistic theory of psychology (movements are "forced" by external stimuli), and especially H. S. Jennings's (1906) objective experimental approach to behavioral adaptation in single-celled paramecia, among other protozoan and lower metazoan organisms. In fact, with the publication of Watson's Behavior: An Introduction to Comparative Psychology (1914) and Psychology from the Standpoint of a Behaviorist (1919), virtually all of the general psychology became objective in methodology. Psychology became the study of behavior (instead of the mind), with the conditioned response (reflex) as its primary unit of analysis and conditioning as its tool. (Not all would agree that psychology should be limited to the study of reflexes or conditioning, so cognitive psychology has become quite popular in the late 1900s.)

Second, Thorndike postulated that all learning involved the Law of Exercise (use and disuse) and the Law of Effect. Therefore, from the comparative-psychological viewpoint, according to Thorndike, animals differed merely in "the delicacy, number, complexity, and permanence of associations." On these measures, dogs were somewhat more intelligent than cats, dogs and cats exceeded fish, monkeys exceeded dogs and cats, and humankind exceeded monkeys. (However, a real "gauge" of intelligence or learning ability—or a genuine application of a gauge—was still lacking.) According to Thorndike, nonhuman animals did not have ideas: Homo sapiens had ideas but these were derived from learning via exercise and effect.

These issues (S-R association and the roles of behavioral activity and reinforcement) have remained prominent to this day in general learning (behavior) theory, which one might define somewhat mischievously as the noncomparative approach to animal intelligence—if we understand by "comparative" the search for species differences as well as similarities not only in behavioral adjustment per se but also in the psychological processes mediating these adjustments. General behavior theory holds that principles of conditioning are applicable across all vertebrate species, including humans, and that cognitive psychology will one day be explicable in terms of principles of conditioning. The power or influence of conditioning theory has waned considerably in the final decades of the 1900s, whereas cognitive psychology is in the ascendancy.

Third, one of Thorndike's least appreciated contributions to comparative psychology is embodied in his notion that as we "ascend" the vertebrate series of animals, we likely have the possibility for the learning of more associations more quickly and lastingly because the trend is for the brain to be larger and thus to have more connections (synapses) in it. Thorndike does not give us his authority for this generalization about the evolution of the brain, but likely he was following Herbert Spencer and the writings of more contemporaneous, neurologically well-versed writers such as the Herrick brothers (Clarence Luther, the originator of psychobiology, and his younger brother C. Judson). In any event, this grand generalization resurfaced, with new trappings, in Hebb's (1949) concept of the A/S ratio: the ratio of association area to sensory projection area of the brain. Although there are no exact figures available, the ratio of association to primary sensory areas increases rather remarkably from the "lower" vertebrates (fishes, amphibians, reptiles) to the "higher" ones (birds and mammals).

By inference, Hebb (1949) assumed this ratio to be relevant "to the greater speed with which the 'lower' species can learn to respond selectively to the environment, and to the comparative simplicity of the behavior when it is fully developed" (p. 126). He also predicted the relevance of the ratio to the slow initial or primary learning of higher vertebrates (especially primates), in which the sensory projections are small relative to the size of the association areas: "If the sensory projection is small, association cortex large, the [environmental] control will take longer; the period of 'primary learning,' that is, will be long" (p. 124). Finally, the larger association area of the higher vertebrates (birds and mammals) would account for their greater efficiency at maturity. For Hebb, the learning capacity of higher species at maturity is not merely the capacity for a greater number of associations (Thorndike); it also reflects an emancipation from direct control by the stimulus of the moment from the immediate environment (i.e., an evolutionary difference in central or psychological mediation).

In recent years, an important tome has appeared to put some meat on the bare bones of Thorndike's and Hebb's speculations on the increase in the size of the brain in the vertebrate lineage: Harry Jerison's Evolution of the Brain and Intelligence (1973). There has indeed been a progressive enlargement of the brain even when the general increase in body size in higher versus lower vertebrates is calculated in the equation. Birds and mammals stand out conspicuously in "encephalization quotient" when compared with lower vertebrates of the same body size: Birds and mammals have "extra neurons" when their brain size is compared to the size it ought to be, given a high correlation between brain and body size across species (not, however, across individuals within a species). The conventional explanation for the increase in brain size in birds and mammals is "that they had invaded new niches in which there was an adaptive advantage for enlarged brains" (Jerison, 1973, p. 16).

With Jerison's elegant statistical formulas we at last have a metric or gauge (however gross it may be) for the evolution of the brain. But what of the evolution of intelligence? Is it valid to continue to ask whether intelligence (learning ability) has evolved in the usual sense that transcends ecological niches and ecological considerations? If so, can it be meaningfully and validly measured in the laboratory? What is the psychological gauge? These issues bedevil us to the present day with supporters on both sides of the controversy.

[Some material for this entry was excerpted, with permission, from G. Gottlieb (1979), Comparative psychology and ethology, in E. Hearst, ed., The first century of experimental psychology. Hillsdale, NJ: Erlbaum.]