Thinking and Deciding

THE PSYCHOLOGY OF HYPOTHESIS TESTING 169
case, there is a single relevant cue, the shape of the little symbol in the upper lefthand
corner of each card. The concept “seven,” in cards, is based on a different cue
— the number printed in the corner (or seven symbols in the middle of the card).
Cues are also called attributes or features of things.
Concept formation
In some cases, the theory holds, a concept is characterized by a conjunction of cues
or features: that is, by all of them together, an “and” relationship. The concept
“seven of spades” is characterized by both the numer and the suit. A “bachelor” is
characterized by the features “unmarried, male, adult.” In other cases, a concept is
characterized by a disjunction of features: that is, one of several features, an “or”
relationship. A “face card” (in some games) is either “a card with a picture” or “an
ace.” “Earned income” consists of “wages, salaries, tips, commissions, etc.”
According to the traditional view in psychology (which is by no means well
accepted today), we ordinarily learn concepts by testing hypotheses about the cues or
features. Consistent with this view is the finding that young children, while they are
first learning the meaning of words such as “dog,” often make mistakes that appear
to be based on incorrect hypotheses that they have not yet eliminated by critical tests
or evidence. A young child might first suppose that the word “dog” refers to any
four-legged animal. Only by trying the word out on cows and being corrected does
the child discover that this hypothesis is incorrect. Similarly, one child used “ba-ba”
to refer not only to herself but to other people, and the cat as well (Ingram, 1971); her
concept was defined by the single feature of animacy. At some point she observed
that adults used the word “baby” to refer only to creatures that were small and human
as well as animate. When testing a hypothesis about the meaning of a word, a child
often has to wait for evidence provided by other people. Adults do not always provide
feedback when a child uses a word incorrectly, so, the theory claims, it is difficult
for children to carry out experiments to actively test their hypotheses. Bruner and his
colleagues also distinguished between “deterministic” and “probabilistic” cues.
Given this view of concepts, psychologists hoped to improve their understanding
of how we learn concepts by asking subjects to learn artificial concepts in the laboratory.
Bruner, Goodnow, and Austin performed a classic set of experiments using this
design (1956). In most of their experiments, the stimuli were cards (special ones,
not an ordinary deck) that varied along four dimensions: number of forms printed
on them (1, 2, or 3); number of borders (1, 2, or 3); type of form (cross, square,
or circle); and color (green, red, or black). Some subjects were asked to discover a
deterministic concept that described a particular category, a subset of the 81 cards.
For example, a category might be “black crosses” or simply “black.” Subjects could
do this by pointing to one of the cards and asking the experimenter whether or not
the card was in the category. This was called a selection experiment, because the
subjects selected the cards. In reception experiments, the experimenter chose the
cards (randomly). The subject guessed whether each card was in the category or not
and received feedback from the experimenter.