Eckhard Hess

(1916 - 1986)

Compiled by Jason Waite (December 1999)

Hess Biography
Time Line

Eckhard Hess was born in Bochum, Germany on September 27, 1916, and the son of an artist, Heinrich Hess. He immigrated to the United States in 1927 where he became a naturalized citizen in 1943. He began his undergraduate studies at Blue Ridge College in Maryland in 1941. Two days after his birthday in 1942, Hess was married to Dorothea Nawiasky. The next year Hess began wartime service in the United States Army for two years. When he returned, he attended Johns Hopkins University for graduate study, earning his M.A. in 1947 and his Ph.D. in 1948.

In 1953, he began his career as an associate professor at the University of Chicago, where he would go on to be head of the Psychology department in 1963 (Gale Literary Databases, 1999). During his time in Chicago, Hess was among those animal behaviorists that revived the study of imprinting in precocial birds, many years after Konrad Lorenz had done his initial work with imprinting (Stevenson, 1967). On imprinting, he published many books alone and with others including New Directions in Psychology (1962), and Imprinting: Early Experience and the Developmental Psychobiology of Attachment (1967). Hess also co-edited Early Behavior: Comparative and Developmental Approaches (1967), and Imprinting (1977).

Hess dedicated the latter part of his life to the study of pupillometrics, which measures pupillary response to viewing emotionally charged stimuli. In 1967, he wrote a book titled The Tell-Tale Eye: How Your Eyes Reveal Hidden Thoughts and Emotions (1975), on this subject (Gale Literary Databases, 1999). Hess died of pneumonia in Cambridge, Maryland, on February 21, 1986.


When Hess set out to study imprinting, he like most psychologists approached it from a learning perspective. It was not long, though, until his research would put imprinting into a different light. His initial research soon showed that there was a difference between imprinting to a human and to a mallard decoy (Burghardt, 1978). Following the work of Lorenz, he looked for characteristics of the releasing stimuli that would strengthen the imprinting behavior. Hess' early work dealt with mallards and ring doves.

He was the first psychologist to take mallards out of their natural setting and bring them into a lab to study imprinting. He was interested in the variability of following behavior to different stimuli. Hess used a unique apparatus to study following behavior in the mallards. He began by putting ducklings of different ages on a circular runway and introducing a male mallard decoy that would rotate around the path (See Figure 1). A microphone was attached to the decoy. By using this apparatus to study following behavior, Hess was able to standardize the test for imprinting and measure how responsive the ducklings were to the decoys. This could be done by vocalizations or distance traveled. The critical period for eliciting this following behavior is between 13 and 16 hours (Ramsey & Hess, 1954). It was this line of investigation that led Hess to believe, "the greater number of stimulus aspects found in the natural mother trigger innate physiological reactions and behavioral responses" (Burghardt, 1978).


Hess also used this circular apparatus in another experiment using chicks. This time, he wanted to see the effect of introducing a mild electric shock to the chick during imprinting. Using a learning approach, one would assume that the duckling would fear the decoy by association, but instead Hess found that imprinting was strengthened in this situation. This showed that the critical period was important in imprinting and was affected by emotional excitation (Hess, 1961). This work led Hess to study the fear response in chicks which, in nature, increases the social bond with the parent animal and ends the critical period (Hess, 1959). The fear response ensures that no imprinting to other animals will take place because after the critical period, the chick exits an area when a strange animal enters (McGill, 1965).

Klinghammer and Hess worked with ring doves to determine sexual preference. Forty-eight ring doves, ranging in age from four to 14 days were removed from their nest to act as subjects. The doves were divided into four groups. The AA group was isolated in individual cages. The AB group was isolated until weaning and then placed in a cage with other ring doves. Subjects in the BA group were raised until weaning by their parents, and then placed in isolation until testing. The BB group was the control because the doves were reared by their parents and lived in a dove community after weaning. After eight or nine months, the doves became sexually mature and were tested for sexual preference between a human and an opposite-sex species member. The AA group preferred humans if isolated at 6-9 days of age. The BA group was mixed, having two choose the human, two choose the ring dove, one choose both, and one choose neither. Both the AB and BB group members chose the species member. This research indicated that for this species, imprinting is reversible (Klinghammer and Hess, 1964).


Another contribution that Hess made was in the intriguing study of pupillometrics in which pupil size and movement is measured to identify emotionally charged or complex stimuli. He initially studied pupillary response with his assistant at the University of Chicago, James M. Polt. They record the subject's eye dilations via a mirror that is angled toward a video camera. (See Figure 2). At first, the subject would look at a control slide with intensity similar to that of the stimulus slide they were about to witness. After viewing the control for approximately 10 seconds, they would be presented with the stimulus for 10 seconds. This pairing of control slide and stimulus slide would be repeated10 to 12 times. Hess and Polt would then measure the average size of the pupil for each of the control and experimental trials (Hess, 1959).

He was initially hesitant to push forward with this line of research because there was a chance that illumination alone could affect the pupillary response. He conducted another experiment in which he used the natural room lighting for the control so that the screen would always be somewhat brighter during the experimental trials. The dependent variable was the percentage change in pupil size. Had the room lighting been the sole factor, the subjects' pupils would have constricted regardless of the stimulus present. Interestingly enough, female subjects tested showed a more positive change in pupil dilation for slides of a baby, a mother and baby, a male "pinup" figure, while the male subjects favored a female "pinup" figure and a landscape. This research showed that interesting or positive stimuli would cause dilation while negative stimuli would cause contraction. This sparked Hess' interest and he began to do more research in the field of pupillometrics (Hess, 1959).

Using similar methods, Hess and Polt presented two identical pictures of a woman that differed in one aspect to a group of 20 men. In one, the size of her pupils had been greatly enlarged; while in the other, her pupils were extremely small. On average, the response by the men for the picture with the large pupils was twice that of the picture with the small pupils. After the experiment was completed, the men were asked to comment on the photographs and most of them stated that the two were identical. Of the few that did not state the photographs were identical, reports were given that one woman was "prettier" or "more feminine" (Hess, 1959). None of those tested had noticed the difference in the pupil size of the woman in the picture.

Another finding by Hess was when he administered math problems while measuring pupillary change. In one study, a subject's pupil size is measured while they perform arithmetic problems mentally. The subject's eyes dilated until the point where the problem was solved and then constricted back to a normal range. In another study, subjects were given four multiplication problems and were measured for percentage change in pupil size. The change in dilation was a measure of how much effort the task took for each subject. The greater the increase in dilation indicated the more cognitive effort used during the task (Hess, 1959).

Time Line
1916 Birth
1927 Immigrated to United States
1941 Received A. B. from Blue Ridge College
1942 Married Dorothea Burghard-Nawiasky
1943 Naturalized as a United States citizen; served in the United States Army
1948 Received Ph.D. from John's Hopkins University
1950 Joined faculty at University of Chicago, IL
1962 Published New Directions in Psychology
1963 Became head of Psychology Department at University of Chicago
1968 Retired from faculty at University of Chicago
1973 Published Imprinting: Early Experience and the Developmental Psychobiology of Attachment
1975 Published The Tell-Tale Eye: How Your Eyes Reveal Hidden Thoughts and Emotions
1986 Death

Bornstein, Marc H., Ed. (1980). Comparative Methods in Psychology. Lawrence Erlbaum Associates: Hillsdale, New Jersey.
Burghardt, Gordon M. and Bekoff, M. (1978). The Development of Behavior: Comparative and Evolutionary Aspects. Garland STPM Press: New York.
Gale Literary Databases (1999) Eckhard Hess (Biography) Retrieved from the World Wide Web on December 2, 1999.
Hess, E. H. (1961) Influence of early experience on behavior. Paper presented before the American Psychological Association, New York State Divisional Meeting.
Hess, E. H., & Hess, D. B. (1969) Innate factors in imprinting. Psychonomic Science, 14(3), 129-130.
Hess, E. H. (1959 In Nebraska Symposium on Motivation, University of Nebraska Press: Lincoln, p.44-77.
Klinghammer, E., & Hess, E. H. (1964) Imprinting in an altricial bird: the blond ring dove. Science, 146, 265-266.
McGill, Thomas E., Ed. (1965) Readings in Animal Behavior. Holt, Rinehart and Winston, Inc.: New York.
Ramsay, O., & Hess, E. H. (1954) A laboratory approach to the study of imprinting. Wilson Bull. 66, 196-206.
Stevenson, Harold W, Hess, Eckhard H., & Rhinegold, Harriet L., Ed. (1967) Early Behavior: Comparative and Developmental Approaches. John Wiley and Sons, Inc.: New York.

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