CHAPTER 01:H OW D OW E KNOW ?
Seemingly immeasurable things can be measured
Object of psychology research attention are elusive concepts such as passion, perception, prejudice,
o We cannot directly observe any of these psychological concepts
o We can make reasonable inferences about psychological concepts by making indirect
AF EWQ UICT IPS FURSINT HIT EXT
Simile: a saying or description in which the communicator explicitly uses one concept to help
people understand or appreciate another – typically by using words such as “like” or “as.”
Reading the Barnum description
o Two Reactions:
You should find it surprisingly accurate
You should be curious to know how it could be so accurate
o Barnum knew that most people readily confuse statements that are true of people in general
with statements that are true of them in particular
o Bui (1997) gave a Barnum description to undergraduates at UCLA, she found that the typical
student reported that it was highly accurate
When asked how well this personality profile described them on a 9-point scale
whose upper endpoint was labeled extremely well, the large majority of students
responded with 7s, 8s, or 9s. (The mean was 7.5, and the most common response was
AB RIEF H ISTORY OF HUMAN K NOWLEDGE
M ETAPHYSICAL SYSTEMS
Earliest explanations for human behaviour (and for the physical world as well) appear to have been
metaphysical or supernatural explanations
Metaphysical systems: an early set of explanations for human behaviour and the operation of the
physical world. Metaphysical explanations attributes behaviour or experience to the operation of
nonphysical forces such as deities. Metaphysical explanations include (1) animism, (2) mythology
and religion, and (3) astrology.
Earliest category of metaphysical explanations for human behaviour was probably animism, the
belief that natural phenomena are alive and influence behaviour.
Second category of metaphysical explanations shares many of the features of animism but is still a
potent force in the lives of people everywhere= mythology and religion (the belief that human
behaviour and experience are influenced by the operation of spiritual forces such as the wishes of a
o In the U.S., about 65% of adults say that religion is an important part of their lives
o In less affluence countries, this figure is considerably higher In both Sri Lanka and
Bangladesh, 99% of adults say that religion is an important part of their daily lives.
o Religious explanations for behaviour are typically more sophisticated and comprehensive
than animistic explanations, but they share the basic assumption that nonphysical, even
magical, forces determine much of what people do.
o Religious systems are built on a different set of assumptions than those upon which scientific
systems are built (though scientists, too, make plenty of assumptions).
o Religious and scientific systems of thought are built upon very different sources of evidence.
A third very old category of metaphysical systems is astrology (the belief that human behaviour and
personality are influenced by the positions of celestial bodies such as planets and stars).
o Adopt some scientific practices in trying to explain human behaviour Example: Serious astrologers are very focused on accuracy and precision in
Believe that to give a person the most accurate astrological reading possible, it
is necessary to know the exact year, month, day, and time of day of that
person’s birth, along with the exact latitude and longitude of the person’s birth
o Astrology is a perfect model of decidedly unscientific ways of thinking
Metaphysical systems were eventually abandoned by scientists in favor of explanations based on an
entirely different approach to knowledge.
Philosophy: the systematic study of human behaviour and experience by means of logic, intuition,
and empirical observation. Philosophers are interested in the nature of knowledge, ethics,
aesthetics, logic, etc. Along with physiology, philosophy was one of the two most important
precursors of psychology.
Early philosophers often borrowed concepts from less scientific ways of thinking
o Many early European philosophers worked hard to make sure their ideas were consistent
with the Bible of with the works of Aristotle or Plato- both of who endorsed some highly
o As late as the 17 century, Descartes transformed thinking about human behaviour into a
scientific enterprise, accepted the argument that nerves were hollow tubes through which
“animal spirits” flowed to the brain
o Maturation of philosophy led its practitioners to rely on logic and empirical observation
o Among contemporary philosophers, arguing for an idea or opinion solely on the basis of
authority is considered a sign of weakness.
Focus on logic among philosophers had its roots in early Greek philosophers such as Plato and
Focus on empirical observation, though championed by Aristotle himself, never really caught on
until the concept got a big jump-start from Descartes in the 1600s.
After Descartes, the value of making empirical observations grew in popularity during the days of
British empiricists such as Locke, Hume and Hartley.
o Principle reached its philosophical heyday after August Comte convinced most 19 century
philosophers that a comprehensive theory of knowledge and human behaviour should follow
the principle of positivism (the idea that sense perceptions are the only basis for knowledge
or certainty (also known as logical positivism)).
o Empiricism: an approach to understanding the world that involves collecting data or making
o By the middle of the 19 century, the concept of empiricism took firm hold in philosophy and
became one of the core assumptions of the scientific method.
Psychology emerged as an independent field of study in the mid-to late 19 century emerged
partly in the wake of philosophy.
Psychologists, usually experimental psychologists place a great deal of stock in systematic
Psychology only owes about half of its genealogy to philosophy
P HYSIOLOGY AND THE P HYSICAL S CIENCES
Philosophers believe in empirical observation
o Few philosophers gather data to test their theories and hypotheses
Psychology probably owes its current emphasis on systematic observation to its roots in the
physical sciences, especially physiology (the study of the functions of an interrelations between
different parts of the brain and body)
Virtually everything we know about physiology has been discovered using the experimental
method. Before William Harvey’s landmark experiments on the circulation of blood in 1628, scientists had
little or no idea that blood is pumped throughout the body by the heart
The tenacious belief that nerves were Lilliputian (i.e., tiny) pipelines for animal spirits was put to
rest once and for all by means of the experimental method
o Few simple experiments conducted by biologists like Luigi Galvani and Alessandro Volta
demonstrated that an electrical charge must be applied to a frog’s nerves to produce muscle
Only when researchers began to experimentally destroy certain parts of the brains of animals were
they able to determine that different areas of the brain performed different physical and
o Example: Marshall Hall’s experiments with decapitated animals in the early 1800s provided
some of the first convincing evidence that the spinal cord and not the brain determine reflex
Two distinct points:
o The experimental method is a powerful way to answer research questions
o The experimental psychologists owe a great deal of what is good about their discipline to the
traditions and methods developed and refined by physiologists and other physical scientists.
Many scientific studies are not experiments
Most historians of psychology would probably agree that psychology first became a science when
psychologists first began to conduct experiments.
EXPERIMENTAL P SYCHOLOGY
Most historians of psychology agree that experimental psychology was invented in Germany
sometime around the mid-to late 1800s.
o Only point of disagreement is whether Fechner, von Helmholtz, Weber, or Wundt invented it
They all studied perceptual and sensory processes in the mid- to late 1800s, and they
all made use of experimental methods.
Wundt was the most psychologically minded one in the bunch
Desire to break consciousness down into its component parts
Heavy emphasis on experimental methods reflected his extensive training in
Interested in higher-order mental processes
o In his earliest and most important words (the Beitrage, published in
1862), he expressed a keen interest in creating a field he called social
psychology, and he eventually published a ten-volume book entitled Folk
Psychology between 1900 and 1920.
Wundt felt that the experimental method that was so crucial to understanding
basic psychological experience was ill-suited to the study of complex cognitive
and social processes
Psychology (the scientific study of human behaviour) has become both decidedly experimental and
How do scientists go about their business?
o Scientists, like pastors, politicians, and pastry chefs, make very important assumptions
o Many of the specific principles can be derived from the general principles that almost all
scientists take for granted
o Fundamental principles that are more or less accepted on faith are often referred to as
At least four such fundamental principles appear to be accepted by almost all
scientists. determinism, empiricism, parsimony, and testability
T HE F OUR C ANONS OF SCIENCE
D ETERMINISM Determinism: the doctrine that the universe is orderly- the idea that all events have meaningful,
Animistic and astrological systems of thought are partly deterministic
o Astrologers appear to believe that something about the motions and positions of celestial
bodies causes people to behave in certain predictable ways
They can’t (or won’t) tell us exactly what it is about Neptune’s rising or Venus’s
falling that causes Serena to have bad luck last Wednesday, but it is presumably
Some psychologists have even argued that people (and perhaps many other animals) are
predisposed to think in causal terms.
o Plenty of evidence suggests that we are wont to do so.
o Example of the power and utility of causal thinking, consider the following problem
(adapted from Tversky & Kahneman, 1982):
A cab was involved in a hit-and run accident at night. Two cab companies, the Green and the Blue, operate in the city.
You are given the following data:
(1) 85% of the cabs in the city are Green ad 15% are Blue.
(2)A witness identified the cabas Blue.
Court tested the reliability of the witness under the same circumstances that existed on the night of the accident and
concluded that the witness correctly identified each one of the two colours 80% of the time and failed 20% of the time.
What is the probability that the cab involved in the accident was Blue?
If you are like most people, your intuitions are telling you that it is about
0.80, which corresponds very well to the reliability of the witness
Tversky and Kahneman (1982) found in their studies:
o The median (middle) and modal (most common) answer for a large
group of participants was 0.80.
o Replace statement (1) in the original problem with the following statement:
(1) Although the two companies are roughly equal in size, 85% of cab accidents in the city involve Green cabs and 15%
involve blue CABS
Think again about the accident, the reliability of the witness, and the probability
that the cab involved in the accident was Blue. What is this probability?
Correct answer hasn’t changed
Your intuitions about the answer may have
When Tversky and Kahneman gave this logically equivalent version of the
problem to a different group of participants, the median answer changed to
0.60, which indicates that participants in this second group were making at
least partial use of information about base rates
Base-rate information is information about the proportion of things in a
target population- in this case, either the proportion of Green and Blue cabs
in the city, or the proportion of Green and Blue cabs involved in accidents.
o People find it easier to think in terms of causality
When you were provided with both base-rate information and some kind of
subjectively useful competing information (in this case, a witness’s report), you
probably did not make very good use of the base-rate information.
If you revised your answer downward once you realized that most accidents in
this city are caused by Green cabs, you improved the accuracy of your judgment by
being more sensitive than usual to base-rate information when it was expressed in
Correct answer to cab problem is 0.41
In light of the facts that (1) Green cabs are 5.67 times as likely to be
involved in accidents as are Blue cabs and (2) the witness’s judgment was
pretty poor (only 30% better than the change performance level of 50%),
you should have adjusted your answer quite a bit in the direction of Green
cabs The fact that most people come a lot closer to the correct answer when the
base-rate information is framed in causal terms attests to the tendency that
people prefer to think, and are possibly predisposed to think, in causal
o Research that deals more directly with how people perceive covariation.
Group Who Harmed the Nems? Who Helped the Nems?
Zarks T, a zark, harmed the nems. E, a zark, helped the nems
N, a zark, helped the nems.
Glorks R, a glork, harmed the nems. A, a glork, helped the nems.
O, a glork, harmed the nems. I, a glork, helped the nems.
P, a glork, helped the nems.
Based on the information in the table, decide which of the two groups, zarks and
glorks, you find more likeable.
If you are like most people, you probably found the glorks at least a little more
likable than the zarks.
If you did conclude that you’d prefer to invite a glork rather than a zark to your
next dinner party, you probably fell prey to a common judgmental bias known as
the illusory correlation (the false association that people often form between
membership in a statistical minority group and rare (and typically negative)
Hamilton and his colleagues found that people falsely infer a connection or
correlation between group membership and the likelihood of engaging in nice
versus nasty behaviors.
More specifically, they typically judge small groups like the zarks to be less
likable than large groups like glorks.
Both groups are exactly twice as likely to help the nems as they are to harm them.
There just happens to be twice as many glorks as zarks.
If we consulted Tversky and Kahneman to help us describe this situation, they
would probably remind us: (1) that base rates for helping are twice as high as they
are for harming, (2) that base rates for glorks are twice as high as they are for
zarks, and (3) that in this case, there is no need to adjust anything for base rates –
except perhaps in the sense that, in light of base rates, there is no reason to be
impressed by the fact that four different glorks helped the nems
Helping is simply popular; glorks are simply populous.
The fact that people often perceive connections where none truly exists plays an important role
in the development and maintenance of stereotypes.
o The statistical minority group (the much maligned zarks) were judged more harshly than
the statistical majority.
People often perceive connections between things that aren’t really connected also suggests that
people may be a little too ready to see the world in terms of causes.
o Behaviorists who condition animals have identified an animal analogue of this judgmental
o B.F. Skinner demonstrated that if you place an animal in a box and drop reinforcements in
a food tray at random intervals (irrespective of what the animal is doing), the animal will