Clever Hans (in German,
der Kluge Hans) was a
horseThe horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
that was claimed to have been able to perform
arithmeticArithmetic or arithmetics is the oldest and most elementary branch of mathematics, used by almost everyone, for tasks ranging from simple day-to-day counting to advanced science and business calculations, such as addition, subtraction, multiplication and division...
and other intellectual tasks.
After formal investigation in 1907,
psychologistA psychologist is someone who studies the human mind and behavior. Research psychologists study human perception, cognition, attention, emotion, motivation, personality, behavior and interpersonal relationships...
Oskar PfungstOskar Pfungst was a German comparative biologist and psychologist. While working as a volunteer assistant in the laboratory of Carl Stumpf in Berlin, Pfungst was asked to investigate the horse known as Clever Hans, who could apparently solved a wide array of arithmetic problems set to it by its...
demonstrated that the horse was not actually performing these mental tasks, but was watching the reaction of his human observers. Pfungst discovered this artifact in the research methodology, wherein the horse was responding directly to involuntary cues in the
body languageBody language is a form of non-verbal communication, consisting of body pose, gestures, and eye movements. Humans send and interpret such signals unconsciously....
of the human trainer, who had the faculties to solve each problem.
Clever Hans (in German,
der Kluge Hans) was a
horseThe horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
that was claimed to have been able to perform
arithmeticArithmetic or arithmetics is the oldest and most elementary branch of mathematics, used by almost everyone, for tasks ranging from simple day-to-day counting to advanced science and business calculations, such as addition, subtraction, multiplication and division...
and other intellectual tasks.
After formal investigation in 1907,
psychologistA psychologist is someone who studies the human mind and behavior. Research psychologists study human perception, cognition, attention, emotion, motivation, personality, behavior and interpersonal relationships...
Oskar PfungstOskar Pfungst was a German comparative biologist and psychologist. While working as a volunteer assistant in the laboratory of Carl Stumpf in Berlin, Pfungst was asked to investigate the horse known as Clever Hans, who could apparently solved a wide array of arithmetic problems set to it by its...
demonstrated that the horse was not actually performing these mental tasks, but was watching the reaction of his human observers. Pfungst discovered this artifact in the research methodology, wherein the horse was responding directly to involuntary cues in the
body languageBody language is a form of non-verbal communication, consisting of body pose, gestures, and eye movements. Humans send and interpret such signals unconsciously....
of the human trainer, who had the faculties to solve each problem. The trainer was entirely unaware that he was providing such cues.
In honour of Pfungst's study, the anomalous artifact has since been referred to as the
Clever Hans effect and has continued to be important knowledge in the
observer-expectancy effectThe observer-expectancy effect is a form of reactivity, in which a researcher's cognitive bias causes them to unconsciously influence the participants of an experiment...
and later studies in
animal cognitionAnimal cognition is the title given to a modern approach to the mental capacities of non-human animals. It has developed out of comparative psychology, but has also been strongly influenced by the approach of ethology, behavioral ecology, and evolutionary psychology...
.
Spectacle
During the late nineteenth century, the public was especially interested in animal intelligence due in a large part to
Charles DarwinCharles Robert Darwin FRS was an English naturalist who realised and presented compelling evidence that all species of life have evolved over time from common ancestors, through the process he called natural selection...
’s then-recent publications.
Hans was a horse owned by a Herr Wilhelm von Osten, who was a
gymnasiumA gymnasium is a type of school providing secondary education in some parts of Europe, comparable to English grammar schools or sixth form colleges and U.S. college preparatory high schools...
math teacher, an amateur horse trainer and phrenologist, and something of a mystic.
Hans was taught to add, subtract, multiply, divide, work with fractions, tell time, keep track of the calendar, differentiate musical tones, and read, spell, and understand German. Von Osten would ask Hans, "If the eighth day of the month comes on a Tuesday, what is the date of the following Friday?” Hans would answer by tapping his foot. Questions could be asked both orally, and in written form. Von Osten exhibited Hans throughout Germany, and never charged admission. Hans's abilities appeared on page six of the New York Times.
Both von Osten and Hans were notoriously bad tempered and prone to rage when the horse did not perform well. Pfungst suffered more than one horse bite during his investigation.
Investigation
Due to the large amount of public interest, the German board of education appointed a commission to investigate von Osten's scientific claims. Philosopher and
psychologistA psychologist is someone who studies the human mind and behavior. Research psychologists study human perception, cognition, attention, emotion, motivation, personality, behavior and interpersonal relationships...
Carl StumpfCarl Stumpf was a German philosopher and psychologist.Born in Wiesentheid, he studied with Franz Brentano and Rudolf Hermann Lotze...
formed a panel of 13 people, known as the
Hans Commission. This commission consisted of a veterinarian, a circus manager, a Cavalry officer, a number of school teachers, and the director of the Berlin zoological gardens. This commission concluded in September 1904 that no tricks were involved in Hans’ performance.
The commission passed off the evaluation to Pfungst, who tested the basis for these claimed abilities by:
- Isolating horse and questioner from spectators, so no cues could come from them
- Using questioners other than the horse's master
- By means of blinders
Blinders, also known as blinkers or winkers, are a piece of horse tack that restrict the horse's vision to the rear and, in some cases, to the side. They usually are made of leather or plastic cups that are placed on either side of the eyes, either attached to a bridle or to an independent hood...
, varying whether the horse could see the questioner
- Varying whether the questioner knew the answer to the question in advance.
Using a substantial number of trials, Pfungst found that the horse could get the correct answer even if von Osten himself did not ask the questions, ruling out the possibility of fraud. However, the horse got the right answer only when the questioner knew what the answer was, and the horse could see the questioner.
He observed that when von Osten knew the answers to the questions, Hans got 89 percent of the answers correct, but when von Osten did not know the answers to the questions, Hans only answered six percent of the questions correctly.
Pfungst then proceeded to examine the behaviour of the questioner in detail, and showed that as the horse's taps approached the right answer, the questioner's
posturePosture or posturing may refer to:In humans* Neutral spine or good posture* Human position* Abnormal posturing, in neurotrauma* Posturography, in neurology* Posture and Occupational HealthIn biology...
and facial expression changed in ways that were consistent with an increase in tension, which was released when the horse made the final, correct tap. This provided a cue that the horse could use to tell it to stop tapping.
The social
communicationAnimal communication is any behavior on the part of one animal that has an effect on the current or future behaviour of another animal. The study of animal communication, sometimes called spencerology has played an important part in the methodology of ethology, sociobiology, and the study of animal...
systems of horses probably depend on the detection of small postural changes, and this may be why Hans so easily picked up on the cues given by von Osten (who seemed to have been entirely unaware that he was providing such cues). However, the capacity to detect such cues is not confined to horses. Pfungst proceeded to test the hypothesis that such cues would be discernible, by carrying out laboratory tests in which he played the part of the horse, and human participants sent him questions to which he gave numerical answers by tapping. He found that 90% of participants gave sufficient cues for him to get a correct answer.
Even after this official debunking, von Osten, who was never persuaded by Pfungst's findings, continued to show Hans around Germany, attracting large and enthusiastic crowds.
The Clever Hans effect
Pfungst made an extremely significant observation. After he had become adept at giving Hans performances himself, and fully aware of the subtle cues which made them possible, he discovered that
he would produce these cues involuntarily regardless of whether he wished to exhibit or suppress them. This gives the phenomenon an importance which could hardly be exaggerated. Its recognition has had a large effect on experimental design and methodology for all experiments whatsoever involving sentient subjects (including humans).
The risk of Clever Hans effects is one strong reason why comparative psychologists normally test animals in isolated apparatus, without interaction with them. However this creates problems of its own, because many of the most interesting phenomena in animal cognition are only likely to be demonstrated in a social context, and in order to train and demonstrate them, it is necessary to build up a social relationship between trainer and animal. This point of view has been strongly argued by
Irene PepperbergIrene Maxine Pepperberg is a scientist noted for her studies in animal cognition, particularly in relation to parrots. She is an adjunct professor of psychology at Brandeis University and a lecturer at Harvard University...
in relation to her studies of
parrotParrots, also known as psittacines , are birds of the roughly 372 species in 86 genera that make up the order Psittaciformes, found in most warm and tropical regions. The order is subdivded in three families: the Psittacidae , the Cacatuidae and the Nestoridae...
s (
AlexAlex was an African Grey Parrot and the subject of a thirty-year experiment by animal psychologist Irene Pepperberg, initially at the University of Arizona and later at Harvard and Brandeis University. Pepperberg bought Alex in a regular pet shop when he was about one year old...
), and by Allen and Beatrix Gardner in their study of the
chimpanzeeChimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:...
WashoeWashoe was a chimpanzee who was the first non-human to learn to use some of the signs of a human language, that of American Sign Language. She also passed on some of her knowledge to her adopted son, Loulis....
. If the results of such studies are to gain universal acceptance, it is necessary to find some way of testing the animals' achievements which eliminates the risk of Clever Hans effects. However, simply removing the trainer from the scene may not be an appropriate strategy, because where the social relationship between trainer and subject is strong, the removal of the trainer may produce emotional responses preventing the subject from performing. It is therefore necessary to devise procedures where none of those present knows what the animal's likely response may be.
For an example of an experimental protocol designed to overcome the Clever Hans effect, see
Rico (Border Collie)Rico is a border collie dog who made the news after being studied by animal psychologist Juliane Kaminski from the Max Planck Institute for Evolutionary Anthropology in Leipzig after his owners reported that he understood more than 200 simple words...
.
As Pfungst's final experiment makes clear, Clever Hans effects are quite as likely to occur in experiments with humans as in experiments with other animals. For this reason, care is often taken in fields such as
perceptionIn philosophy, psychology, and the cognitive sciences, perception is the process of attaining awareness or understanding of sensory information. It is a task far more complex than was imagined in the 1950s and 1960s, when it was predicted that building perceiving machines would take about a decade,...
,
cognitive psychologyCognitive psychology is a discipline within psychology that investigates the internal mental processes of thought such as visual processing, memory, problem solving, and language....
, and
social psychologySocial psychology is a type of social science that is concerned with individuals' thoughts, feelings and behavior as they affect or are affected by other individuals...
to make experiments
double-blindThe blind method is a part of the scientific method, used to prevent research outcomes from being influenced by either the placebo effect or the observer bias. To blind a person involved in research is to prevent them from knowing certain information about the process...
, meaning that neither the experimenter nor the subject knows what condition the subject is in, and thus what his or her responses are predicted to be. Another way in which Clever Hans effects are avoided is by replacing the experimenter with a computer, which can deliver standardized instructions and record responses without giving clues.
Popular culture
References to the Clever Hans effect have appeared in TV shows and songs. In an episode of
The SimpsonsThe Simpsons is an American animated television sitcom created by Matt Groening for the Fox Broadcasting Company. The series is a satirical parody of a middle class American lifestyle epitomized by its eponymous family, which consists of Homer, Marge, Bart, Lisa, and Maggie...
("
Smart and Smarter"Smart and Smarter" is the thirteenth episode of The Simpsons
' fifteenth season, and originally aired on February 22, 2004. When Maggie takes an IQ test, she is informed that she may be smarter than Lisa, who worries that her life will go nowhere. The episode was written by Carolyn...
"), Lisa Simpson becomes jealous of her baby sister Maggie after Maggie is discovered to have an even higher IQ than the precocious Lisa. Later in the episode, Lisa is relieved to find that she had been unconsciously cueing Maggie's correct IQ-test answers.
Military officer
Günther von KlugeGünther “Hans” von Kluge was a German military leader. He was born in Posen into a Prussian military family. Kluge rose to the rank of Field Marshal in the Wehrmacht.-Early career:...
was nicknamed
Der Kluge Hans (Clever Hans) in admiration of his brilliance. Von Kluge went on to become one of the most able Field-Marshals of the Third Reich.
See also
- Pygmalion effect
The Pygmalion effect, or Rosenthal effect, refers to the phenomenon that the greater the expectation placed upon people, often children or students, the better they perform...
- Lady Wonder
Lady Wonder was a horse belonging to Virginia farmgirl C. D. Fonda, which was said to have psychic abilities. Over 150 thousand people came to consult the horse at the price of three questions for one dollar; it has been suggested that many of the questions had to do with betting on race horses....
a horse with purported telepathic abilities.
- Ideomotor Effect
The ideomotor effect is a psychological phenomenon wherein a subject makes motions unconsciously. As in reflexive responses to pain, the body sometimes reacts reflexively to ideas alone without the person consciously deciding to take action...
Sources
Hothersall, David. History of Psychology. McGraw-Hill. 2004.
- Pfungst, O. (1911). Clever Hans (The horse of Mr. von Osten): A contribution to experimental animal and human psychology (Trans. C. L. Rahn). New York: Henry Holt. (Originally published in German, 1907).
External links