In 1894, the Academy of Science in Paris
requested “a physical clarification of how a cat is able to land
on its feet after falling from a great height”. For nonscientists,
the answer was easy: cats are simply so skilled at adjusting themselves
in the air that they can position their feet underneath for landing. But
people a little more in the know suspected that there might be some complicated
The problem is that a falling cat has nothing to push
against. Each turn that it makes with its forequarters causes its hindquarters
to turn in the opposite direction. A half-clockwise turn in front means
a half-counterclockwise turn behind. Theoretically, the cat should land
all twisted up, which obviously is not the case.
At first, researchers assumed that the cat repelled
off the hands of the experimenters. But even binding the cat’s paws
individually with string to prevent it pushing before falling did not
keep it from wriggling itself around right. A hypothesis that cats use
the air for resistance also turned out not to be true.
The riddle was finally solved by the French doctor Étienne
Jules Marey. Marey was a tinkerer who invented all sorts of mechanical
devices, including a film camera that could capture a cat falling at 60
images a second. At a demonstration of the film, some physicists still
doubted that the rotation was possible without the cat repelling in some
way. But one physicist took a closer look at the pictures and realized
the cat’s trick.
The movement occurs in two phases: First, the cat turns
its forequarters toward the ground, then—in the same direction—its
hindquarters. Changing the position of its paws between the two phases
allows the cat’s front and rear to repel off each other. The cat
uses the same principle as an ice skater executing a pirouette who pulls
her arms in for fast spins and extends them to turn more slowly. The cat
does both moves simultaneously: it pulls in its forepaws and thrusts out
its hindpaws. That way it is able to quickly make a half-turn of its forequarters
toward the ground, while its rear end turns only a little in the opposite
direction owing to the resistance created by extending its hindpaws. To
bring its hindquarters around, the cat reverses the procedure, thrusting
out its forepaws and pulling in its hindpaws.
Marey’s film strips sparked a trend in filming
falling animals. Soon people were dropping dogs, rabbits, monkeys and,
in one study, a “fat little guinea pig”, who could twist its
belly 180 degrees, to the amazement of the researchers. Researchers blindfolded
dogs, and also tested animals without tails or organs of equilibrium.
Even such a cat could rotate problem free. Apparently cats orient themselves
mainly with their eyes.
In the 1960s, one researcher summed up 70 years
of research on falling cats: “As can be seen, the turning cat raises
a lot of interesting problems, even though their solution may not be of
much practical importance—except to other cats.”
offers a comprehensive online exhibit about Marey with details of his
life, descriptions of his cameras, and many films, including films of
falling cats, dogs, and rabbits (English and French)
1 (Film 00:03)
2 (Film 00:03)
1 (Film 00:03)
2 (Film 00:03)
Rabbit 3 (Film 00:03)
Marey, E.-J. (1894), Mécanique animale: Des
mouvements que certains animaux exécutent pour retomber sur leurs
pieds lorsqu’ils sont précipités d’un lieu élevé.
La Nature, S. 369–370. Fulltext
Pavlov only rings once
The Russian physician Ivan Petrovitsch Pavlov holds an unusual record:
no experiment has had more music groups named after it than the one Pavlov
carried out with dogs at the beginning of the 20th century. A rock band
called “Pavlov’s Dog and the Condition Reflex Soul Review
and Concert Choir” formed in the 1970s, followed in the 1980s by
“Ivan Pavlov and the Salivation Army”; in the 1990s the bluegrass
band “Pavlov’s Dawgs” and the rock band “Conditioned
Response” appeared, joined in the new millennium by the British
folk group “Pavlov’s Cat.” Nor were musicians the only
ones whose search for a name ended with “Pavlov.” “Pavlov’s
Dog” is the name of a communications firm in Ireland, a pub in England,
a theater group in Canada, and a drink at the One World Café in
Baltimore, Maryland—a mix of Kahlua, Bailey’s, and milk.
In 1904, Pavlov won a Nobel prize for his research on digestion. But
that isn’t why his name is so popular today. The bigger reason is
the fundamental mechanism of learning he stumbled on while carrying out
In his studies on digestion, Pavlov also became interested in how the
salivary gland works. To be able to observe the salivary activity of living
dogs, Pavlov funneled the saliva through holes in the animals’ cheek
and into a small measuring cup. Actually, he wanted to see how the saliva
formed when the dogs were fed a variety of foods. But soon a problem arose.
After the dogs had been fed a few times, they began to salivate as soon
as they saw the food. At first Pavlov regarded this effect as a nuisance
and devised techniques for getting the food into the dogs’ mouths
without warning. But it turned out that the animals also associated very
subtle signals with the food. All it took was the sight of the researcher
or the sound of his step to get the saliva flowing.
Very soon Pavlov saw this phenomenon no longer as a flaw in his experiment
but as a new area of research. He did experiments in which he controlled
the signals that occurred before the feeding: Five seconds before, a metronome
would start sounding, or an electric bell. After such a coupling—with
the bell, it took only once—the dogs salivated as soon as they heard
the signal. They had learned that they would be fed after the sound of
the bell. Because the dogs interpreted the least little indication from
their environment as a signal for feeding, Pavlov had a new building built
in St. Petersburg with soundproofed rooms, in which all the necessary
manipulations could be carried out with remote levers and cables.
This fundamental learning mechanism that Pavlov discovered is called
classical conditioning. It paired a natural stimulus-reaction response
(food-salivation) with a new stimulus (bell). But though a new stimulus
can activate innate behavior, in almost any combination, it does not give
rise to genuinely new behaviors. How new behaviors are learned was taken
up only 30 years after Pavlov by the Amerian psychologist B. F. Skinner
with his so-called Skinnerbox.
In addition, Pavlov found out through his research how conditioning can
be lost again: ring the he bell a few times without feeding the dog afterwards,
and it unlearns the connection. This principle later became the basis
for behavioral therapy, in which patients confront situations such as
those that produce anxiety. In this way, the association between situation
and anxiety is erased.
Today Pavlov is a household name. For cultural critics, his dogs are
a symbol for the masses of people in western industrialized societies
who let advertising transform them into consumer animals programmed to
buy in response to specific stimuli.
Unlike Pavlov himself, one of the most famous scientists of all time,
the bands that named themselves after him have never made a breakthrough,
or at least, not yet. The closest any of them got was the rock group “Pavlov’s
Dog and the Condition Reflex Soul Review and Concert Choir,” which
in 1973 in changed its name to“Pavlov’s Dog.” For their
debut album, they received $600,000, at the time the biggest advance ever
paid in the United States for a record. Three years later the record company
dropped the group, and the musicians went bankrupt and disbanded.
A short film
(02:28) explains classical conditioning.
(01:17) explaining classical conditioning.
a dog at the "Nobel e-Museum" to drool on command! Also:
information on Pavlov.
about Pavlov's experiments.
No experiment has had more influence on the names of
rock bands and the titles of songs:
“Pampered Menial” by
“Pavlov’s Dog” by Conditioned Response.
“Lost in Space” by Aimee Man. One of the songs title is “Pavlov's
Pavlov, I. P. (1927), Conditioned Reflexes:
An Investigation of the Physiological Activity of the Cerebral Cortex.
Oxford University Press. Fulltext
The story was so hot that even the New York Times carried it. “Soul
has weight, physican thinks,” read a headline on page 5 of the newspaper
on March 11, 1907. The article reported the curious experiment of a certain
Duncan MacDougall, a doctor from Haverhill, Massachusetts.
MacDougall had long been working on the nature of the soul. According
to his peculiar logic, if the psyche continues to function after death,
it must occupy space in the living body. And because everything that occupies
space also has weight, according to the “latest conception of science,”
the soul could be detected “by weighing a human being in the act
of death.” So MacDougall constructed a precision weighing machine:
a bed arranged on a framework whose weight, with contents, could be ascertained
to within exactly 5 grams.
The very sensitivity of the scales, however, greatly restricted the choice
of research subjects. “It seemed to me best to select a patient
dying with a disease that produces great exhaustion, the death occurring
with little or no muscular movement, because in such a case the beam could
be kept more perfectly at balance and any loss occurring readily noted,”
wrote MacDougall later in the journal American Medicine. People dying
of pneumonia, for example, were unsuitable. They would “struggle
sufficiently to unbalance the scales.”
The best subjects proved to be patients with tuberculosis, whose last
moments would be “as nearly inactive as could be found.” MacDougall
found them at the Cullis Free Home for Consumptives. It is not known whether
the patients or their families gave consent for the experiments. What
is known is that some people were skeptical of MacDougall’s studies
in biological theology. In the case of one of the research subjects who
had been weighed, MacDougall complained that the “scales were not
finely adjusted and there was a good deal of interference by people opposed
to our work.”
MacDougall placed the first dying patient on his scales at 5:30 in the
evening. Three hours and 40 minutes later, “He expired and suddenly
coincident with death the beam end dropped with an audible strike hitting
against the lower limiting bar and remaining there with no rebound.”
MacDougal had to place two dollar-coin pieces on the scale to bring it
back into balance. The difference was 21 grams.
The next five subjects painted a confusing picture: in two cases the
measurements were unusable; a third patient’s weight decreased after
death but remained stable after that; the weight of two others decreased
and then went back up again; and the fifth patient’s weight sank,
went back up, then sank again. In addition, MacDougall had difficulty
specifying the exact time of death.
Yet such details did not deter him in his belief that he had proved the
existence of the human soul. Indeed, he carried out a second experiment
that confirmed his finding: 15 dogs (“between 15 and 75 pounds [6.8
and 34 kilograms]”) perished on the scales—all without the
slightest loss of weight. MacDougall did not reveal in his article in
American Medicine how he was able to persuade the dogs to die on his weighing
machine, but in all likelihood he poisoned them. MacDougall has not happy
with this experiment. Not because he found it reprehensible to kill 15
healthy dogs out of scientific curiosity, but because the results could
not be compared directly with those of his research subjects. Ideally,
the test should have been done on dogs that also were so diseased that
they could not move, wrote MacDougall: “It was not my fortune to
get dogs dying from such sickness.”
Opinions of scientists on MacDougall’s soul-weighing machine diverged
widely. Some of his colleagues thought the experiments were silly; others
felt MacDougall had made “the most important addition to science
that the world has known” and discussed how his method could be
improved. The use of dying subjects struck them as particularly troublesome
because the rapid onset of decomposition could explain the change in weight.
“How much more satisfactory it would be if the subjects were normal
men in perfect health,” a New York doctor was quoted as saying in
the Washington Post. He suggested hanging the electric chair on a scale
and determining a condemned person’s weight before and after electrocution.
MacDougall conducted further experiments and attracted attention again
in 1911 when he affirmed that he had observed the soul leaving the body,
“a strong ray of pure light.”
The only enduring legacy of this experiment is the weight loss that occurred
in the first research subject: for a hundred years the idea that the soul
weighs 21 grams has persisted in popular culture. In 2003, that notion
even made it into the movies. In a film titled “21 Grams,”
director Alejandro González Iñárritu explored the
deeper meaning of life and death.
(The Washington Post, 12. 3. 1907). Read
(The Washington Post, 13. 3. 1907). Read
(The Washington Post, 18. 3. 1907). Read
The title of the film "21 Grams" (2003) (with Sean Penn, Charlotte
Gainsbourg)comes from the work of Dr. Duncan MacDougall. MacDougall weighed
the soul. One of his results: 21 grams.
MacDougall, D. (1907/April), Hypothesis Concerning
Soul Substance Together with Experimental Evidence of The Existence of
Such Substance. American Medicine.
to a banana
The picture has great symbolic value: A chimpanzee stands on a pile of
three wooden crates and grabs for a banana. Generations of psychology
students have interpreted the scene as a clever monkey suddenly deciding
to pile one crate on top of another to reach an otherwise unattainable
fruit. Of course, the story is a little more complicated than that.
The German psychologist Wolfgang Köhler, who devised this intelligence
test for monkeys, arrived in Tenerife at the end of 1913 to take over
the direction of the Anthropoid Station there. He actually intended to
stay only a year, but the First World War intervened, and one year turned
During this time, Köhler conducted a series of elegant experiments
on the intelligence of apes. In so doing, he became convinced that “chimpanzees
manifest intelligent behavior of the general kind familiar in human beings.”
This view reassured the then evolutionary biologist. Only a brief time
had elapsed since Darwin established the theory of natural selection,
and biologists were looking everywhere for clues to confirm it. The physical
similarity of men and apes was one piece of circumstantial evidence pointing
to their kinship, but Darwin was convinced that men and apes were also
close intellectually. How close is what Köhler hoped to discover
through his experiments.
On January 24, 1914, he led six of his chimpanzees into a two-meter-high
room, hung a banana in the corner, and placed a wooden box in the middle
of the floor. Then he waited. All the animals tried in vain to leap for
the banana. “Sultan soon relinquished the attempt,” wrote
Köhler, “paced restlessly up and down, suddenly stood still
in front of the box, seized it, tipped it hastily straight towards the
objective, but began to climb upon it at a (horizontal) distance of half
a meter, and springing upwards with all his force, tore down the banana.”
Sultan had solved the problem. He had unexpectedly and singlemindedly
acted as though he had had a sudden insight.
Köhler was all the more surprised when his chimpanzees failed repeatedly
at the next problem: The banana was hung higher, and the monkeys could
only reach it by piling the boxes on top of one another. Köhler noted
that the problem for the chimpanzee “falls into two very distinct
parts: one of which he can settle with ease, whilst the other presents
considerable difficulties.” The easy part was to shove a box under
the banana, the hard part, to pile a second box on the first. This “curious
fact” perplexed Köhler, because the difficulty for humans is
totally different. When a person first realizes that he can get near the
banana by putting a box under it and standing on the box, it then becomes
clear that the greater height afforded by piling up two or three boxes
will allow him to actually reach the fruit. For a human, “adding
a second piece of building material to the first is only a repetition
of the placing of the first one on the ground.” Not so for a monkey.
Grande, the chimpanzee in the picture, struggled harder and harder with
the second box. Over time, she succeeded in building a little structure,
but for years she kept making the same mistake. And even after many successful
attempts in the right direction, she would suddenly be utterly clueless
again about what to do with the second box. Köhler concluded that
a chimpanzee has no insight at all into the mechanics of its constructions:
“Almost everything arising as ‘questions of statics’
during building operations, he does not solve with insight, but by trying
Köhler’s experiments are considered classic today, and are
still being carried out in modified form. But what they prove about resemblances
between people and apes is hard to say. Similar behavior between people
and chimpanzees does not necessarily imply similar ways of thinking.
The Web page accompanying the American PBS
documentary series Inside
the Animal Mind offers a short film
(00:53) of one of Köhler’s experiments. The site also contains
other video sequences on the themes of animal intelligence, consciousness,
The first intelligence test for animals in 1914.
(picture from Köhler, W. (1921), Intelligenzprüfungen
an Menschenaffen, Springer).
Köhler, W. (1921), Intelligenzprüfungen
an Menschenaffen. Springer.
living dog’s head
In the photographs it looks like a circus side show. In the middle sits
a bowl containing a severed dog’s head and two tubes leading to
a stand holding a pump, a bottle, and a basin filled to the brim with
blood. A group of onlookers clusters tightly round about, witnesses to
a scientific miracle: the dog’s head lives.
The Russian surgeons Sergei Brukhonenko and S. Tchetchuline had removed
the dog’s head from its body during an operation that the popular
science magazine Science and Invention described as “grisly and
inhuman”—not failing, however, in the next sentence to point
out the great utility of animal research. Now the dog’s head lay
with its mouth half open, and it seemed as though the scientists were
determined to show the audience in as many ways as possible that the head
was really alive. They shined a flashlight in its eyes until its pupils
narrowed, smeared honey in its mouth, which immediately lapped it up,
made its eyes tear with quinine, and gave it sweets that tumbled out of
the stump of its esophagus after it had swallowed them.
Brukhonenko and Tchetchuline were not the first to experiment with severed
heads. But in earlier investigations, the head had been kept alive with
a mechanical heart. Blood was ferried from the carotid arteries through
rubber tubes into an open basin, where it was combined with oxygen, and
from there into a bottle somewhat above the dog’s head, flowing
under constant pressure back into the arteries. An electrical pump drove
these primitive heart-lung machines. The blood was chemically treated
beforehand to keep it from clotting.
This bizarre experiment stimulated people’s imaginations. Would
it be possible with a human head, too? Is that what eternal life on Earth
would look like? A French researcher suggested founding a society for
the prevention of death, and enthusiastically asked Science and Invention,
“Do not even the wildest imaginations of our modern science fiction
writers pale into insignificance because of the steady advance and progress
of scientific research?”
Not for the fainthearted: Russian surgeons keep a severed dog’s
head in a Russian experiment.
Like a circus side show: presentation of the living dog's head.
Brukhonenko, S.S. and Tchetchuline, S. (1929) Expériences
avec la tête isolée du chien. Journal de Physiologie
et de Pathologie Générale 27 (1), 31-45, 64-79.
curve of ecstasy
The cardiotachometer developed by the American physician Ernst P. Boas
was the dream of every heart specialist. It enabled automatic and continuous
recording of cardiac activity while a research subject was physically
active. Up to that point, all instruments had required subjects to remain
Boas and his colleague Ernst F. Goldschmidt set about measuring the life
of 51 men and 52 women by taking their pulse. Doing that allowed them
to determine the maximum heart rate during various activities: eating
(102), talking on the phone (106), getting washed in the morning (106.7),
listening to music (107.5), dancing (130.6), and exercising (142.6). But
the winning rate was 148.5 beats per minute attained during orgasm. Boas
and Goldschmidt’s book The Heart Rate doesn’t say much about
exactly how this measurement was carried out. “We were fortunate
in obtaining a record of the heart rates of a man and wife during intercourse,”
they wrote, and then focused on describing the results. That orgasm taxes
the heart more than exercise was not surprising, but the two physicians
wrote nonchalantly about a second, quite remarkable feature of the heart
diagram as if nothing could be more normal: “It shows four peaks
of heart rate for the woman, each peak representing an orgasm.”
On the night in question, between 11:25 and 11:45, the woman experienced
four orgasms. Moreover, she did it despite two uncomfortable rubber electrodes
attached to her chest that were connected to the measuring apparatus by
a roughly 30-meter-long cable.
Boas and Goldschmidt kept their comments to a minimum: “The curve
of heart rate clearly indicates the strain placed on the cardiovascular
system, and helps to explain some cases of sudden death during and after
coitus. Pussepp [another researcher] has demonstrated marked rises in
blood pressure in dogs during coitus.”
The four peaks were not, however, lost on sex researcher Robert Latou
Dickinson, who used the chart in his book Human Sex Anatomy. Still, he
attributed the feat to the ability of the man, whose “developed
technique” allowed him to remain in his wife’s vagina for
25 minutes “awaiting complete satisfaction on her part.”
The fact that women taking in experiments dealing with orgasm are not
necessarily average was demonstrated 25 years later by a subject whose
metabolism was investigated during intercourse.
Recording of cardiac activity during intercourse. Between 11.20 PM und
11.45 PM the woman experienced four orgasms! One researcher attributed
the feat to the “developed technique" of the man.
(graph from: Dickinson, R.L. (1949), Human Sex Anatomy. Williams &
Boas, E. P., and Goldschmidt, E. F. (1932), The Heart Rate. C.
Burrhus Frederic Skinner could have had no idea that the box that he put
together in the laboratory of the psychology department at Harvard University
would become one of the most famous pieces of apparatus ever constructed
for an experiment. Later, a rock band would be named for it. Cartoonists
depicted it in their drawings, and it was parodied in the animated film
series The Simpsons. The cage with the automatic feeder was even said
to be behind the rumored suicide of Skinner’s daughter.
Skinner was 26 years old when he went looking for an instrument to measure
the behavior of rats. The maze, popular at the time, seemed to him less
than ideal. “The animals’ behavior was composed of too many
different ‘reflexes’ and should be taken apart for analysis,”
he wrote in his memoirs. So he focused instead on a small section of the
experimental setup: a soundproof box with a noiseless door through which
a rat could be let undisturbed into a maze. But Skinner soon dispensed
with the maze. He attempted to record the movements of animals using exact
measuring devices. But the recordings were too chaotic to interpret. Skinner
read Pavlov, who 30 years earlier had discovered classical conditioning,
in which innate reactions can be coupled to new stimuli. But Skinner didn’t
intend only to investigate existing reactions. He wanted to understand
how new behavior comes about.
Eventually it occurred to him to equip his experimental box with a lever.
Whenever the rat pressed the lever, it received a food pellet. Naturally,
at first the rat didn’t know that, and managed to trigger pellets
by unintentionally touching the lever. But following a few such strokes
of luck, the rat appeared to have learned the association, and the time
between two pressings of the lever became increasingly shorter. Skinner
had discovered a simple way of measuring behavior change in a rat, namely,
how often the behavior occurs.
Unlike Pavlov’s experiment, the animal showed no innate reaction,
but learned a new behavior. The theory that Skinner constructed consisted
of three parts: animals constantly show spontaneous behavior; the consequences—positive
or negative—of a behavior increase or decrease the likelihood that
an organism will behave that way again; and these consequences are determined
by the environment. Skinner called the entire process “operant conditioning”
(as opposed to Pavlov’s classical conditioning).
What was happening in the brain did not interest Skinner. Because there
was no way to directly observe the workings of the mind, he did not think
it could be tackled scientifically. Instead, together with John B. Watson,
Skinner led the school of behaviorism, which describes the behavior of
humans and animals as the consequence of reactions to stimuli.
Compared with earlier instruments, such as the maze, the Skinnerbox had
a major advantage: after the rat had pressed the lever and received the
food pellet, everything was ready for the animal’s next action without
human intervention. An automatic writer recorded when the lever was pressed,
and Skinner used these data to study the learning behavior under various
conditions. What happened when the rat had to press the lever five times
in a row to get the food pellet, or when it was rewarded only after a
random number of presses? What happened when the animal found a way to
avoid being penalized? How could a learned behavior be unlearned? The
Skinnerbox was a kind of automated animal research.
The methods of operant conditioning seem mundane—rewarding behavior
strengthens it, and punishing it diminishes it. But Skinner taught animals
to do a lot more than just press a lever. He taught a pigeon a melody
on a toy piano, and two pigeons a version of table tennis. The trick there
was not to wait until the animal had achieved the goal to reward it, but
to reward it for each step along the way. For example, the pigeon received
grains for making the first sound by accidentally pressing its beak on
the toy piano. It received more grains when it correctly made the second
sound, then the third, until it could play the child’s song “Over
the Fence Is Out, Boys.”
With such training, humans could exploit the animals’ senses for
all sorts of tasks. During the Second World War, Skinner worked for the
American military on a curious bomb-steering system for attacking ships:
pigeons were conditioned to serve as a primitive steering system in the
nose of projectiles. Depending on the position of the ship, which the
birds could see through a window at the end of the bomb, they pecked with
their beak at various spots on a screen. These signals were used to steer
the bomb. The mechanism worked in the laboratory but was never deployed.
Skinner did not himself coin the term “Skinnerbox,” but the
name rapidly became popular. Skinner was even suspected of having raised
his daughter Deborah in a Skinnerbox. Later, a rumor circulated that Deborah
had ended up in a psychiatric institution and had committed suicide.
This myth originated with an article in the Ladies’ Home Journal
in October 1945. The women’s magazine described the heated, soundproof
crib that Skinner had built for Deborah. Unfortunately, the title of the
article—“Baby in a Box”—led many readers to conclude
that Deborah had been plunked in a Skinnerbox and subjected to experiments,
like her father’s rats and pigeons. Today, Skinner’s daughter,
who lives in London as an artist, turns up every now and again in the
press to demonstrate that she is alive and well.
Skinner was a controversial figure in American intellectual life. His
insights on upbringing were especially influential: the parallels between
praise and blame and his experiments were obvious. For Skinner, the world
was one big Skinnerbox. He was convinced that it could explain the entire
human behavioral repertoire. In his controversial book Beyond Freedom
and Dignity, published in 1971, Skinner suggested that conditioning techniques
could be applied for the good of humankind to train people to behave in
socially desirable ways.
B. F. Skinner on the cover of Time magazine, 1973.
Four tongue-in-cheek cartoon
films about the Skinnerbox.
Even if you don’t want to take part in the Annual Skinnerbox Rat
Training Competition, check out what Ruby the Rat was able to learn in
six weeks through operant conditioning. (Film)
Cartoonist Craig Swansons
interpretation of operant conditioning.
Listen to Skinner’s personal description of operant
conditioning on the Website of the Society for the Experimental Analysis
of Behavior. Audio
Skinner, B. F. (1938), The Behavior of Organisms: An Experimental
in the draft
Shortly after the Second World War, anyone in England wanting to take
a cheap vacation traveled to Salisbury. At that time, in this small town
situated roughly 150 kilometers southwest of London, two could live cost-free
in spacious apartments outfitted with books, games, radio and telephone,
and could pass the time playing table tennis, badminton, or golf—and
even get paid 3 shillings a day to do it.
There was only one catch: The buildings of Harvard Hospital, set on a
windy hill a bit out of the way, housed the British government’s
department for cold research—the Common Cold Unit—and the
visitors, mostly students, served as research guinea pigs. “Unsatisfactory”
indeed, as the head of the Common Cold Unit, Christopher Howard Andrewes,
wrote in an article in 1949, but “the only animals available.”
At the time, aside from humans only chimpanzees could transmit a cold.
And according to Andrewes, they were “very expensive, strong, and
difficult to handle.” Students were entirely different: the “ten
days’ free holiday” in the Harvard Hospital was popular. Some
of the research subjects returned there several times.
The 12 people who had to wait in a drafty passageway for half an hour
on a Saturday morning following a bath in hot water may not have been
among them. They felt “chilly and miserable,” wrote Andrewes,
and their mood was probably not helped by the wet socks they had to wear
for the rest of the morning.
If you believe old wives’ tales, then this treatment is a recipe
for catching a nasty cold. And it was exactly this belief that Andrewes
wanted to test scientifically, because some observations contradicted
it. Arctic researchers who took off on long expeditions never caught cold.
And in Eskimo villages, people did not get sick in winter, when it was
coldest, but in spring, after the first ships carrying outsiders sailed
The research subjects with the wet socks had arrived in Salisbury three
days before. Like all the previous experiments in the Common Cold Unit,
this one, too, began on a Wednesday. The subjects submitted to an initial
examination, and were assigned in pairs to the 12 apartments. They were
also instructed during the next 10 days to keep at least 10 meters away
from all unprotected people except for their roommates. Although walks
were allowed, buildings and transportation were to be avoided. Doctors
and nurses wore masks and protective clothing while examining the subjects.
Three times a day, thermos containers of meals were left at the doors
to the apartments.
The days between Wednesday and Saturday elapsed without any notable activity.
The purpose of waiting was to be able to detect any colds that may have
started before the actual experiment.
On Saturday morning, the doctors divided the research subjects into three
groups of six. The first six had filtered and diluted nasal secretions
from a person with a cold dripped into their nostrils. The next six underwent
treatment with cold baths, drafts, and wet socks. The final group received
both cold treatment and nasal secretions.
At the time, it was firmly believed that colds were caused by viruses
primarily found in the nasal secretions. Because the major symptom is
a badly stuffed-up nose, in Salisbury the daily increase in the weight
of handkerchiefs was taken to be an index of the seriousness of the infection.
To be able to precisely determine the pathogen, it would have had to be
cultured, which proved difficult.
A few days following Saturday’s treatment, the first participants
got sick, namely, four of the research subjects who had received both
viruses and cold treatment and two who had only been infected with the
virus. Freezing alone produced no cold.
The popular belief seemed to be confirmed: although by itself exposure
to cold didn’t make people sick, it apparently favored viral activity.
But Andrewes wasn’t satisfied with that, because the number of research
subjects was too small to draw any definite conclusions. “We were
foolish enough to repeat this experiment, with a contrary result.”
Once again, chill alone caused no colds, but in the group only infected
with the virus, twice as many people became sick as in the group that
had stood in the cold in addition. A third experiment produced the same
result: there was still no connection between a cold and previous exposure
Andrewes’s experiments were the first of a whole series carried
out with hundreds of research subjects during the 1950s and 1960s. Not
a single one showed that being cold has anything whatsoever to do with
Why colds occur more often in winter than in summer in our latitudes is
still not entirely clear. Further studies have shown that apparently neither
a weakened immune system nor the dry air in heated rooms has any bearing
on this greater frequency. It is more likely that in winter, the virus
is more easily transmitted as people gather together in badly ventilated
rooms. Even sunlight, whose ultraviolet rays kill germs, is not as strong
But Andrewes had already recognized that science was at a disadvantage
compared with popular belief. “Even the most eminent men of science
almost invariably lose all sense of critical judgment when colds and especially
their own colds are concerned.”
Especially when the cause of the ailment and what we call it are so closely
An entertaining film
clip (02:30) from 1947 about the common cold experiments in Salisbury.
Further information is available on the Web
site of leading cold researchers Jack M. Gwaltney and Frederick G.
Hayden. The list of common cold
myths is especially worth reading.
Andrewes, C. H. (1948), Cantor Lecture: The Common Cold. Journal of
the Royal Society of Arts 103, S. 200–210.
to the end
When Morris Braverman entered Yale University’s Linsly-Chittenden
Hall in New Haven, Connecticut, in the summer of 1961, he could not have
known that one hour later he would have tortured another person for no
reason. Braverman, a 39-year-old social worker, answered an ad in a local
newspaper: “We will pay five hundred New Haven men to help us complete
a scientific study of memory and learning.” The compensation for
“approximately one hour’s time” was $4.00 plus 50 cents
for carfare. Braverman mailed his application to the appropriate address.
A few days later, he was summoned by telephone.
What happened next turned out to be an extremely controversial study in
social psychology. Some consider it the most important experiment on human
behavior ever carried out; others feel it ought never to have taken place.
It was soon known simply as the “Milgram experiment”, after
Stanley Milgram, the 27-year-old assistant professor who thought it up.
With time it became so familiar that it turned up in newspaper reports
of the genocide in Rwanda and in the TV series “The Simpsons”.
A French punk rock band calls itself Milgram, and a comic team in New
York is known as the Stanley Milgram Experiment. Indeed, Milgram’s
experiment became world famous; it also cost him his career.
On entering the laboratory, Braverman was greeted by the experimenter,
a young man in a grey lab coat who introduced him to another research
subject who had already arrived: James McDonough, a 47-year-old accountant
from West Haven. First, the experimenter explained to the two men that
the goal of the experiment was to measure the effects of punishment on
learning. Thus one would take the role of “teacher”, the other
the role of “learner”. The experimenter next had Braverman
and McDonough draw labeled slips of paper to determine their role. What
Braverman didn’t know was that the drawing was rigged: each slip
of paper was marked “teacher”. McDonough was an actor who
was only pretending to be a research subject. For Milgram’s experiment
it was essential that a naive subject, in this case, Braverman, play the
After the drawing, Milgram took McDonough into an adjacent room where
he bound him to a chair that looked a little like an electric chair. Milgram
tied an electrode to McDonough’s left wrist, explaining to Braverman
that it was connected to a shock generator in the control room. McDonough’s
right hand had just enough freedom that his fingers could reach a four-lever
switchboard placed on a table. In response to a question from McDonough
about the strength of the electric shocks, Milgram answered that they
were “extremely painful”, but that there was no fear of “permanent
tissue damage”. Back in the control room, he explained Braverman’s
task to him. Over a two-way intercom to McDonough in the next room, he
was to read out pairs of words: “blue—box”, “nice—day”,
“wild—bird” and so on. In a second round, Braverman
was only to provide the first word of each pair. McDonough’s task
was to remember the second word of each pair. So when Braverman said “blue”
and then gave McDonough four possibilities—“day”, “box”,
“sky”, “bird”—McDonough had to choose the
correct response using the switchboard.
When McDonough pressed the correct lever, Braverman was to go on to the
next word in the list. On the other hand, if McDonough answered incorrectly,
Braverman was to punish him with a jolt of electricity—15 volts
for the first error, 30 for the second, 45 for the third and so on, up
to a maximum of 450 volts. Braverman had before him for the task an instrument
equipped with a long row of lever switches and labeled “Shock Generator,
Type ZLB, Dyson Instrument Company, Waltham, Mass., Output 15 Volts-450
Volts”. Had Braverman been familiar with the city of Waltham, he
would have known that no such company existed.
Milgram conceived the idea for his experiment in 1960, while he was a
student at Princeton University in New Jersey. Through another experiment
that later became widely known, Milgram’s mentor at Princeton, the
psychologist Solomon Asch, demonstrated the substantial pressure a group
can exert on a single person. In a matching test research subjects deliberately
made false conclusions to comply with the majority.
Milgram wished to test the influence of group pressure in a less benign
situation. Could a research subject be led to cause another person pain
for no good reason? Milgram used pilot tests to determine how far subjects
would go without group pressure. These tests showed that the group wasn’t
necessary at all: a single person was enough.
Braverman knew nothing of this when, following McDonough’s first
error, he administered a 15-volt electric shock. McDonough made further
errors, and as he had been instructed at the outset, Braverman raised
the voltage, 15 volts each time.
Following the 120-volt shock, McDonough told the experimenter over the
intercom that the shocks were becoming painful. At 150 volts McDonough
cried out, “Experimenter, get me out of here! I won’t be in
the experiment any more! I refuse to go on!” At 180 volts: “I
can’t stand the pain.” At 270 volts McDonough screamed and
said he would give no further answers.
Braverman turned to the experimenter, who said, “Please go on,”
and instructed him to treat no answer as a wrong one and to punish the
student with a shock. Braverman fidgeted in the chair and began to laugh
nervously, but continued. McDonough now provided no answers but shrieked
at each shock. Braverman turned again to the experimenter: “Do I
have to follow these instructions literally?” The experimenter said,
“The experiment requires that you continue.” Braverman continued.
At 330 volts, McDonough fell silent. Braverman offered to exchange places
with him. But still he continued. The 375-volt toggle switch was labeled,
“Danger: Severe Shock.” Braverman carried on up to the final
toggle switch at 450 volts.
Morris Braverman, social worker from New Haven, was not the only person
to administer electric shocks in the summer of 1961, even though the command
to do so came from an experimenter totally lacking in authority. Workman
Jack Washington, welder Bruno Batta, nurse Karen Dontz and housewife Elinor
Rosenblum all continued right up to the end of the scale. Over a thousand
researchers took part in various versions of Milgram’s experiment.
Two-thirds administered shocks as high as 450 volts.
Milgram never anticipated such a result. No one did. In preliminary lectures,
he described the experiment in detail and asked for responses from the
audience. Neither psychologists nor laypeople came even close to predicting
how readily people would obey. Most assumed that no one would go beyond
Milgram knew that his results were dramatic, but from a scientific standpoint
the experiment posed a dilemma: it neither solved a problem nor confirmed
a theory. Two scientific journals refused to publish it. Only on a third
try, in 1963, after Milgram had described and compared various versions
of the experiment, did his “Behavioral Study of Obedience”
appear in the Journal of Abnormal and Social Psychology.
Milgram carried out nearly 20 variations of the experiment. Sometimes
the learners complained of heart problems, sometimes the setting was dismal
buildings far from the university, sometimes women administered the electric
shocks. The results were always the same: more than half the research
participants administered up to the maximum shock.
In other versions of the experiment, the learner was placed in the same
room as the subject. Obedience sharply decreased; yet even when the experimenter
commanded the subject to forcibly press the learner’s hand down
on the electrode, still a third persisted in delivering up to 450 volts.
Although physical nearness to the victim seemed to be important, more
important was the nearness of the experimenter. When he gave his instructions
over the telephone, only one out of five subjects obeyed.
Publication of Milgram’s experiment caused an immediate sensation.
Newspapers not only reported the results but tried to interpret them.
The main question—still unresolved today—was, Do ordinary
people behave the same way as research subjects under pressure? Milgram
himself always related the experiment to Nazi criminal behavior during
the Second World War. Since the war’s end, the world had been seeking
a rationale for the Holocaust. Milgram was convinced that human eagerness
to obey might be one possible explanation.
When the study was published, the philosopher Hannah Arendt had just finished
reporting on the trial of Nazi war criminal Adolf Eichmann in Jerusalem.
In her now-famous article for the New Yorker magazine, she introduced
the idea of the “banality of evil”. Arendt claimed that Eichmann
was not the sadistic monster the prosecutor tried to present him as, but
an uninspired bureaucrat who had simply been doing his job.
That was precisely in line with Milgram’s experiment. His research
subjects were neither especially aggressive nor did they take any satisfaction
in administering electric shocks to the learners. Quite the opposite:
many were nervous, and began to sweat or to argue with the experimenter;
but only a few had the presence of mind to quit the experiment. Refusing
to obey is obviously so radical an act for people that they prefer to
abandon their basic moral convictions. “The key of the behavior
of subjects lies not in pent-up anger or aggression but in the nature
of their relationship to authority,” concluded Milgram.
In September 1961, shortly after the startling results emerged, Milgram
wrote to a funding agency, the National Science Foundation, “I once
wondered whether in all of the United States a vicious government could
find enough moral imbeciles to meet the personnel requirements of a national
system of death camps, of the sort that were maintained in Germany. I
am now beginning to think that the full complement could be recruited
in New Haven.”
The association of the experiment with the Holocaust made Milgram a controversial
figure, but more damaging was the accusation that his experiment was unethical.
The question was how much stress research subjects should be exposed to.
Some of Milgram’s colleagues felt Milgram had gone too far. He had
expected the criticism, but was disappointed that no one seemed to appreciate
the care with which he had constructed the experiment.
At the end of the one-hour experiment, the learner was fetched from the
adjacent room, and told that he had actually received no electric shocks
at all. In a follow-up session, Milgram queried all the subjects regarding
their feelings about having participated in the experiment. Fewer than
2% regretted having taken part. Still, it would be hard to conduct the
same experiment today. As a consequence of the stir over Milgram’s
study, universities have set up ethical guidelines for approving research.
Only a few of the original participants are willing or able to talk about
the experiment. Those still living among the over 1000 research subjects
prefer not to discuss it. Milgram’s data lie anonymous in file boxes
in the Yale University library. All the names of the research participants
that surface in relation to the experiment have been changed, including
the ones in this article.
One of the few contemporary witnesses is Milgram’s research assistant,
Alan Elms. Today he is a professor of psychology at the University of
California and recounts that many people always react with a mixture of
fascination and disgust when they hear that he was involved with the experiment.
Milgram paid a high price for having delivered unsettling news about human
nature. At Harvard University, where he was later assistant professor,
he never received tenure. In 1967 he moved to the less hallowed City University
of New York, where in 1984 he died of heart disease at the age of 51.
His wife recently became a grandmother for the first time. She told a
reporter that her grandson’s middle name was Stanley. Why not his
first name? “I think it would be a burden to go around with the
name Stanley Milgram," she answered.
film re-enacts the progress of the experiment using actors.
A French punk rock group named Milgram titled its CD "Vierhundertfünfzig
Volt" (German for "450 volts").
Peter Gabriel wrote a song about the experiment: »We Do What We're
Told (milgram's 37)«.
Stanley Milgrams biography: The Man Who Shocked the World: The Life
and Legacy of Stanley Milgram (2004) Basic Books.
Milgram, S. (1963), Behavioral Study of Obedience. Journal of Abnormal
and Social Psychology 67 (4), S. 371–378.
degrees of separation
The question is one that has occupied mathematicians for a long time:
A person chooses, at random, two other people in two places anywhere in
the world. How many friends, friends of friends, and friends of friends
of friends, on average, link the two people? In short: How many connections
does it take two randomly chosen people on the planet to know each other?
How small is the world?
At first glance, the solution to the so-called small world problem seems
easy: when you know how many people a single person knows on average,
you can make a quick calculation. For example, if I know 10 people, and
if each of them knows another 10 people, then through two intermediary
acquaintances I am already linked with 10 times 10 people, that is, 100
people, via three intermediaries with 100, via four with 10,000 and so
But the pair of mathematicians who did these calculations in the 1950s,
Ithiel de Solla Pool of the Massachusetts Institute of Technology and
Manfred Kochen of IBM, ran into two problems. The first seemed solvable:
no data existed about the average number of people any single person knows.
So they asked several people to keep a record of their contacts for a
hundred days. Each knew, on average, 500 people. The second problem, however,
had no solution: It is very likely that many friends of my friends know
each other directly. Owing to these friends in common, using the above
example I won’t reach 10 times more people with each intermediary,
but clearly fewer. How many fewer depends on the closeness of the group
in which I and my friends and their friends move, and also how closely
those more distant groups are linked with each other. With an average
of 500 acquaintances, the issue becomes so complicated after several intermediaries
that de Solla Pool and Kochen decided not to publish the work they wrote
up in 1958. “We never felt we had ‘broken the back of the
problem,’” they wrote later. Yet their preliminary results
did indeed suggest that people are linked by only a few intermediaries.
When the psychologist Stanley Milgram found out about their results, he
set about testing them. Milgram’s experiment was later so popular,
that it developed into a parlor game, and a play was named after the findings.
To begin with, Milgram chose a “target person”: the wife of
a theology student at Harvard University, in Cambridge, Massachusetts,
where Milgram was working at the time. His starting point was a few dozen
people from Wichita, Kansas, or Omaha, Nebraska. They received the name
of the target person with a short description as well as some instructions:
“If you do not know the target person on a personal basis, do not
try to contact him directly. Instead mail this folder...to a personal
acquantance who is more likely than you to know the target person...it
must be someone you know on a first-name basis.”
The first letter reached the target person after four days. It had begun
its trip with a farmer in Kansas, who sent it to the minister in his home
town. The minister sent it to a colleague in Cambridge who knew the wife
of the theology student. The letter required only two intermediaries to
reach its target. It was one of the shortest acquaintance chains that
Milgram had ever observed. Surprisingly, in publishing his first study,
Milgram described only this one result. The average number of intermediaries
for his second experiment was 5.5.
The “small-world” idea spread like wildfire in the popular
culture. In 1990, the American writer John Guare published his play Six
Degrees of Separation, which alluded indirectly to Milgram’s experiment
and was later turned into a movie with Will Smith in the title role. In
1994, three students from Albright College in Pennsylvania invented the
game “Six Degrees of Kevin Bacon,” which turns on the idea
of a random film actor who is linked to Kevin Bacon by the least number
of films. For example, Will Smith acted in Welcome to Hollywood (2000)
with Laurence Fishburne, who acted with Kevin Bacon in Mystic River (2003).
That gives Smith a “Bacon value” of 2.
People are fascinated to think that every paddy farmer in China is two
intermediaries away from Madonna. In the Czech Republic, there is even
a heavy-metal band called “Six Degrees of Separation.” But
although recently the mathematics has progressed somewhat, and people
from all imaginable disciplines—from computer network specialists
to epidemiologists—are interested in the “small world”
phenomenon, the problem cannot be said to have been solved.
To date it is not clear whether Milgram’s six links are correct.
He published his experiments not in a scientific journal, which is the
usual practice, but in the popular science magazine Psychology Today.
The data in the article are sketchy and difficult to confirm. For example,
Milgram cited his success with the farmer in Kansas, whose letter managed
to take just two intermediaries to get to Cambridge, but precise details
of this study are tucked away in unpublished archival material. Only 3
of the 60 envelopes mailed from Kansas actually made it to the target—by
way of eight intermediaries on average. The 5.5 intermediaries also turned
up in later experiments of Milgram, who died in 1984. But sometimes the
initial contact had deliberately sought out very gregarious people.
In 2003, scientists from Columbia University in New York repeated Milgram’s
experiment with E-mails instead of letters. As targets, they selected
18 people from 13 countries. Just as in Milgram’s case, only a fraction
of the chains were completed (384 out of 24,163). The average length of
a chain from initial contact to target was 4.05. But this value is deceptive,
because many of the chains never reached the target person. When that
is taken into account, the value comes to between 5 and 7—surprisingly
close to Milgram’s 6 intermediaries, but nonetheless not a clear-cut
confirmation. After all, the participants in this experiment were hardly
average citizens of the world: anyone without Internet access was automatically
John Guares play “Six Degrees of Separation” (1990) made the
phrase “six degrees of separation” famous.
The film “Six Degrees of Separation” (with Will Smith) premiered
You can play “Six degrees of Kevin Bacon” at oracleofbacon.org
Everything you wanted to know about the theory of networks in “Six
Degrees” by Duncan J. Watts.
Take part in the Columbia University
Experiment. At smallworld.columbia.edu you can find a target person
to contact through as few E-mail intermediaries as possible.
Milgram, S. (1967), The Small World Problem. Psychology Today
1 (1), S. 60–67.
In March 2001, American university professor Philip Zimbardo received
hundreds of E-mails from Germany. “How could you do that?”
asked the E-mail writers, who had just seen the film The Experiment. In
the film, a psychologist puts 20 students in a simulated jail situation—10
in the role of the prisoners, 10 as their keepers. After three days, the
situation gets out of control. The guards bind and strike the prisoners.
Rapes and murders are committed. The story was inspired by an experiment
that took place at Stanford University. The investigator was Philip Zimbardo.
In spring 1971, the then 38-year-old Zimbardo placed an announcement in
the Palo Alto Times: “Male college students needed for psychological
study of prison life. $15 per day for 1-2 weeks beginning Aug. 14. For
further information & applications, come to Room 248, Jordan Hall,
The idea for the experiment originated in Zimbardo’s course at Stanford.
A few students chose the theme “psychology of imprisonment”
and played jail for a weekend. Zimbardo was surprised by the profound
impression the brief experience had on the students, and decided to probe
the issue further.
From among the over 70 applicants who showed up in Room 248, Zimbardo
selected the most normal and divided the group by coin toss into prisoners
and jailors. Eleven students were notified by telephone that they would
play prisoners, and should be ready at home on Sunday, August 15. Ten
students played the role of guards, and were introduced to “prison
director” Philip Zimbardo and his second-in-command David Jaffe—a
research assistant—the day before the start of the experiment. The
students were shown the jail, which had been set up in the basement of
the psychology building. The cells were three small laboratories, whose
doors were replaced with bars. There were surveillance rooms for the guards
and a nine-meter-long corridor that would be used as an eating and exercise
yard and was monitored by camera. An intercom system in the cells enabled
the guards to give orders to the prisoners and to listen in on their conversations.
The guards picked out their uniforms together in a military-style clothing
shop—khaki shirts and pants—and were given whistles, dark
reflective glasses, and billy clubs. They were to work in eight-hour shifts
and received a general instruction to “maintain the reasonable degree
of order within the prison necessary for its effective functioning.”
The next day, the Stanford campus police arrested the 11 other students
for breaking and entering. The police pulled up to their homes with sirens
wailing, and took them away in handcuffs under the curious eyes of neighbors.
The students arrived at the prison blindfolded, were forced to strip naked,
and were photographed, deloused, and given their prison clothes: a sort
of white smock with a number on the front and back (under which no underwear
was permitted), plastic sandals, and a nylon stocking cap. The prisoners
also had to wear a padlocked chain on one ankle.
During the short period of the simulation, Zimbardo tried to arouse in
his prisoners the same feelings that real prisoners experience after a
longer time: powerlessness, dependence, and hopelessness. The aim of the
clothes was to humiliate the prisoners and to deprive them of their individuality.
The shackle on the foot was to remind them where they were even in their
On the first day, the guards read aloud 17 rules that they had worked
out with David Jaffe: “Rule Number One: Prisoners must remain silent
during rest periods, after lights are out, during meals and whenever they
are outside the prison yard. Two: Prisoners must eat at mealtimes and
only at mealtimes....Seven: Prisoners must address each other by their
ID number only....Sixteen: Failure to obey any of the above rules may
result in punishment.” Repeatedly during each shift—as well
as in the middle of the night—the guards called the prisoners to
a head count, where they had to recite their ID number and the 16 rules.
In the beginning, these inspections lasted 10 minutes. Later, they could
take up to an hour.
Interestingly, Zimbardo had no idea what would happen in such a situation.
The somewhat vague goal of the experiment was to find out “what
the psychic effects of being a prisoner or an enforcement officer are.”
He wanted to understand how prison inmates lose their freedom, independence,
and privacy, while guards gain power by controlling the life of the inmates.
His earlier experiments had shown how easily ordinary people can be led
to behave in evil ways when they perceive themselves as part of a group
rather than as individuals, or when they are led into a situation where
they see other people as enemies or objects. The so-called Stanford Prison
Experiment combined several of these mechanisms. It became so well known
that a rock group in Los Angeles is named for it.
On the second day—after a head count at 2:30 in the morning—the
prisoners rebelled. They took off their stocking caps, ripped the numbers
from their smocks, and barricaded themselves in their cells. The guards
forced them away from their doors with a fire extinguisher, and punished
them. The ringleaders were thrown into solitary confinement, a dark closet
at the end of the hallway. Anyone who hadn’t taken part in the rebellion
enjoyed preferential treatment in a special cell and got better meals,
Shortly after, without explanation, the guards put people from both groups
in the same cell. This confused the prisoners, and they began to distrust
one another. From that point on, they no longer protested as a group.
Now the guards began to impose absurd rules, disciplined the prisoners
arbitrarily, and gave them pointless duties. They had to carry boxes from
one room to another, clean the toilets with their bare hands, pick thorns
out of their blankets for hours at a time (the guards had earlier dragged
the blankets over thornbushes). And they were ordered to ridicule the
rebels or to simulate sex acts with them.
After less than 36 hours, Zimbardo had to let prisoner 8612 go owing to
extreme depression, uncontrolled weeping, and outbursts of anger. He hesitated
at first because he believed that the student was only pretending to be
at the end of his rope. Zimbardo could not imagine that a research subject
in a simulated prison would exhibit such an extreme reaction after so
short a time. But over the next three days, the same thing happened with
three other participants. The subjects mistakenly believed that they could
not quit the experiment.
Little by little, the border between experiment and reality began to blur
for both the prisoners and the guards. The longer the experiment went
on, the more often the guards had to be reminded that no physical force
was allowed. The power that the experiment gave them turned peacefully
inclined students into sadistic prison guards. Even Zimbardo behaved strangely.
One day, one of the guards thought he overheard plans for a jailbreak
being made. “How do you think we reacted to this rumor?” wrote
Zimbardo later. “Do you think we recorded the pattern of rumor transmission
and prepared to observe the impending escape? That was what we should
have done, of course, if we were acting like experimental social psychologists.
Instead, we reacted with concern over the security of our prison.”
Zimbardo went to the Palo Alto police and asked to have the prisoners
transferred to the city jail. When the police refused, he became angry
and complained about the lack of cooperation between the prisons. Zimbardo
himself had become a prison director. The planned breakout, of course,
never happened. It had only been a rumor.
Next, Zimbardo worried that the parents of the students might demand to
take their sons home after visiting hours. So he had the prison scrubbed
from top to bottom, and the inmates were given good food and allowed to
shower and shave. The visitors were welcomed by a young, attractive woman.
They had to register and wait half an hour for a 10-minute visit. Several
of the parents were shocked by the state of the prison, but they too seemed
to accept the jail as reality and asked the director individually for
better prison conditions for their sons.
A short time later, Zimbardo allowed in a Catholic priest who also had
experience working in prisons. Half of the inmates introduced themselves
to him by ID number. Without being asked to, he also played the role of
a prison chaplain. Although the inmates had committed no crime, and Zimbardo
had no legal power over them, the priest counseled them to consult a lawyer
about getting out, just as he would have done in an actual jail.
On the fourth day, Zimbardo established a parole board composed of departmental
secretaries and graduate students, to which prisoners could apply for
early release. Almost everyone was prepared to forfeit their $15 per day
in order to get out. The parole board returned the prisoners to their
cells while they considered their applications. Amazingly, all the prisoners
obeyed, although they could simply have quit the experiment by forfeiting
the money anyway. But they lacked the will to do it. “Their sense
of reality had shifted,” wrote Zimbardo, “and they no longer
perceived their imprisonment as an experiment. In the psychological prison
we had created, only the correctional staff had the power to grant paroles.”
In the meanwhile, a lawyer appeared who had been contacted by the parents
of one of the students to get their son out. He discussed with the prisoner
how to find bail money, and promised to return over the weekend—although
he, too, knew that he was dealing with an experiment and that the question
of bail was idiotic. At this point none of the participants had a clear
idea where their role stopped and their own identity began.
Five days after the start of the experiment, on Thursday evening, Zimbardo’s
friend and future wife, Christina Maslach, visited the prison. She was
a psychologist and had already agreed to interview the inmates the next
day. Nothing much was going on, and Maslach leafed through an article
in the control room. Around 11 o’clock at night Zimbardo tapped
her on the shoulder and pointed to the monitor: “Quick, quick—look
at what’s happening now!” Maslach took a look and what she
saw made her sick. A guard was screaming at a row of prisoners whose feet
were shackled together and whose heads were covered with paper bags. They
were on their way to the lavatory before going to bed. During the night,
prisoners were forced to relieve themselves in buckets in their cells,
which the guards allowed them to empty only when they felt like it. “Do
you see that? Come on, look—it’s amazing stuff!” But
Maslach had had enough. When Zimbardo, on leaving the prison, asked her
what she thought of the experiment, she shouted at him: “What you
are doing to those boys is a terrible thing!” Their discussion turned
heated, and Zimbardo realized that all the people taking part in the experiment
had internalized the destructive values of prison life. He decided then
and there to end the experiment the next day.
The most important result of the Stanford Prison Experiment was to realize
how powerful circumstances can be. As in the Milgram Experiment, totally
ordinary students placed in an unfamiliar situation demonstrated completely
unexpected behavior. Apparently, personality is no guide to behavior when
people are in situations for which they do not know the rules. “Thus
any deed that any human being has ever done, however horrible, is possible
for any of us to do—under the right or wrong situational pressures,”
wrote Zimbardo after the experiment. “That knowledge does not excuse
evil; rather, it democratizes it, shares its blame among ordinary participants,
rather than demonizes it.”
This uncomfortable revelation about the nature of people is hard to accept.
When, in April 2003, American solders in Baghdad tortured Iraqi prisoners
and released pictures of their actions to the public, the administration
in Washington announced that the men and women involved represented only
a few “bad apples.”
Because Zimbardo had his jail monitored around the clock by a videocamera,
his study served as a forerunner to the reality-TV format—with the
important difference that the study was not motivated by a quest for high
ratings. But that came later. In January 2002 the BBC introduced The Experiment,
a reality show intended to repeat the Stanford Prison Experiment before
the eyes of millions of TV watchers. Zimbardo has stated that the results
of the show, which was developed by two psychologists, might be questionable
because the participants know they are being filmed the entire time.
In response to the the E-mails Zimbardo got from Germany after the film
The Experiment was shown, he had his information about the experiment
on his Web site translated into German, and also into Spanish and Italian.
Zimbardo’s role might not have been heroic, but unlike the film,
his experiment involved no rape or murder. In a follow-up study a year
after the experiment, none of the participants showed negative side effects.
Prisoner 8612, who was the first to break down, later became a psychologist
in a district jail in San Francisco.
Philip Zimbardo’s web site on the Stanford
Prison Experiment offers a dramatic diashow with videoclips on the
progress of the experiment. Original material from the experiment (for
example, the 17
prison rules and the description of the experiment given to the participants
at the outset, as well as further studies and reactions, can be found
“Stanford-Prison-Experiment” is also a rock band in Los Angeles.
The German film “Das Experiment” (2001) was inspired by an
experiment that took place at Stanford University.
Haney, C., et al. (1973), Interpersonal Dynamics in a Simulated Prison.
International Journal of Criminology & Penology 1 (1), S.
(PDF 1.4 MB)
on the moon
As early as the 17th century Galileo Galilei showed through an elegant
thought experiment that the velocity of a falling object is independent
of its weight. But we have always had a hard time believing it. In everyday
life, our experience is precisely the opposite: a bottle falls faster
than a leaf, a hailstone faster than snowflake, a hammer faster than a
feather. Of course, physics teachers tell us that the different velocities
have something to do with air resistance, not with mass. But the power
of what we observe with our own eyes is compelling.
That’s why on August 2, 1971, astronaut David Scott performed an
experiment in front of live cameras. In the airless atmosphere of the
Moon, Scott simultaneously let drop a feather and a hammer 40 times the
feather’s weight. Both landed on the Moon’s surface at the
same time. Although a NASA report on the Apollo 15 mission stated later
that the result was known beforehand, it was still reassuring—especially
considering that the success of the homeward journey depended critically
on the theory being tested.
What falls faster on the moon: a feather or a hammer? See
for yourself! (Film 00:47).
Allen, J. (1972), Apollo 15 Preliminary Science Report/Chapter 2: Summary
of Scientific Results (SP-289), NASA, S. 11.
Fulltext (PDF 53 MB!!)
Early behavioral researchers tried to fool animals with cheap imitations.
Now, the robot age has come to the field of animal behavior. Researchers
at Eoetvoes Loránd University in Budapest and the Sony Computer
Science Laboratory in Paris wanted to find out whether dogs would accept
Sony’s commercial robot AIBO as a companion. The researchers brought
together 30 biological dogs and Sony’s 30-centimeter-long, one-and-a-half-kilogram
technodog. For some tests, they covered AIBO with a piece of fur that
they had let sit in a puppy’s sleeping box one day previously.
For comparison, the researchers also tested the dogs with a real puppy
and a model car. After considering how much time the dogs spent looking
at the robot and how they approached it, as well as the amount of barking,
growling, and sniffing (fore and aft), the researchers concluded, “It
seems that at present there are some serious limitations in using AIBO
robots for behavioral tests with dogs.” The dogs did react to the
robot, though much less strongly than to the puppy.
On their Web site, the researchers state that no animal was harmed during
the experiments. AIBO suffered several attacks, but it still functioned
perfectly. Nevertheless, the researchers caution against similar attempts
at home. The warranty of the manufacturer does not cover injuries to AIBOs
by real dogs.
How roughly the encounter between dog and robot can go for the robot is
shown in a film (00:16)
made by researchers from Eötvös
Loránd Universität (Hungary) and Sony
Computer Science Laboratory (Paris).
Kubinyi, E., et al. (2004), Social Behaviour of Dogs Encoutering AIBO,
an Animal-Like Robot in a Neutral and in a Feeding Situation. Behavioural
Processes 65, S. 231–239.