Estes, died quietly at the age of 92. His health had declined steadily in the last three months since his wife of almost 70 years, Kay, died in May. Since then he had spoken repeatedly of wanting to join her. As per his wishes, he was cremated and interred with Kay and their son, Greg, in Illinois.
Our friend, mentor, and colleague, BillWilliam K. Estes’ long and productive career encompassed the science of learning and memory from behaviorism to cognitive science, with seminal contributions to both. Estes (born June 17, 1919) began his graduate studies under the tutelage of B. F. Skinner during the early 1940s.
The United States had not yet entered World War II. The Germans were using a new technology — rockets — to bomb England. As Londoners heard the whine of the rocket engines approaching, they stopped whatever they were doing — eating, walking, or talking — and waited for the explosions. After the rockets dropped elsewhere and people realized they were safe, they resumed their daily activities. Intrigued by these stories from London, Estes and Skinner developed a new conditioning paradigm for rats that was similar, in some respects, to what Londoners were experiencing. This paradigm, called conditioned suppression, was a new technique for studying learned fear (Estes & Skinner, 1941). Estes and Skinner placed hungry rats in a cage that delivered food pellets whenever the rats pressed a lever. The cage also had a metal grid floor wired to deliver a mild shock to the rats’ feet. Normally, the hungry rats pressed the lever to obtain food; but if the experimenters trained the rats to learn that a tone predicted an upcoming shock, the rats would freeze when they heard the tone and wait for the shock. Measuring this freezing behavior allowed Estes to quantify trial-by-trial changes in the learned response. Within a few years, this conditioned emotional response paradigm became one of the most widely used techniques for studying animal conditioning, and it is still in use today.
As soon as he completed his PhD, Estes was called into military service. He was stationed in the Philippines as the commandant of a prisoner-of-war camp, a not-very-demanding job that gave him lots of free time to read the mathematics books sent from home by Kay. When the war ended, Estes returned to the United States and to the study of psychology. Much to Skinner’s dismay, Estes soon began to stray from his mentor’s strict behaviorism. He started to use mathematics to describe mental events that could only be inferred indirectly from behavioral data, an approach quite unacceptable to behaviorists. Years later, in his autobiography, Skinner bemoaned the loss of Estes as a once-promising behaviorist, speculating that Estes’ preoccupation with mathematical models of unobservable mental events was a war-related injury, resulting perhaps from too much time in the hot Pacific sun (Skinner, 1979).
Estes built on Hull’s mathematical modeling approach to develop new methods for interpreting a wide variety of learning behaviors (Estes, 1950). Most learning theorists of that era, including Hull, assumed that learning should be viewed as the development of associations between a stimulus and a response. For example, suppose that a pigeon is trained to peck whenever it sees a yellow light in order to obtain a bit of food. Hull assumed that this training caused the formation of a direct link between the stimulus and the response and that later presentations of the yellow light would evoke the peck-for-food response. Estes, however, suggested that what seemed to be a single stimulus, such as a yellow light, was really a collection of many different possible elements of yellowness and that only a random subset of these elements are noticed (or “sampled,” in Estes’ terminology) in any given training trial. Only the elements sampled on the current trial were associated with the response. On a different trial, a different subset is sampled, and those elements were now associated with the response. Over time, after many random samples, most elements became associated with the correct response. At this point, any presentation of the light activated a random sample of elements, most of which are already linked with the response.
Estes called his idea stimulus sampling theory. A key principle of the theory is that random variation (“sampling”) is essential for learning, just as it is essential for the adaptation of species in Charles Darwin’s theory of evolution through natural selection (Estes, 1950). Estes’ approach gave a much better account than other theories (such as Hull’s) of the randomness seen in both animal and human learning, and his theory helped to explain why even highly trained individuals don’t always make the same response perfectly every time. On any given trial, it’s always possible that (through sheer randomness) a subset of elements will be activated that are not linked to the response. Estes also showed how stimulus sampling theory explains how animals generalize their learning from one stimulus (e.g., a yellow light) to other, physically similar stimuli (e.g., an orange light), as Pavlov had demonstrated in the 1920s.
Estes’ work marked the resurgence of mathematical methods in psychology, reviving the spirit of Hull’s earlier efforts. Estes and his colleagues established a new subdiscipline of psychology called mathematical psychology, which uses mathematical equations to describe the laws of learning and memory. From his early work in animal conditioning, through his founding role in mathematical psychology, to his later contributions to cognitive psychology, W. K. Estes continued to be a vigorous proponent of mathematical models to inform our understanding of learning and memory
W.K. & K.W. Estes Fund
William K. Estes (June 17, 1919 – August 17, 2011) had an enormous influence on psychological science, from his pioneering work in mathematical psychology to his collaborations with colleagues to his mentoring of students, many of whom are now leaders in the fields of learning and memory. He was recognized for his lifetime of contributions with our nation’s highest scientific honor, The National Medal of Science.
Bill also had a special role in APS’s history and success as Founding Editor of our flagship journal Psychological Science. During those years, his wife, Katherine W. (Kay) Estes, served as Founding Managing Editor. Bill and Kay were a team in so many undertakings. The W.K. & K.W. Estes Fund celebrates their contributions to psychological science.
Make a contribution online atwww.psychologicalscience.org/estes-fund
A downloadable form is also available on that webpage.
-Mark Gluck,
Rutgers University
Henry L. “Roddy” Roediger, III
Washington University