Conditioning and Learning 359adjustments do not always reflect a greater learning capacity
in humans than in other species. As a result of evolution in
concert with species-specific experience during maturation,
each species is adept at dealing with the tasks that the
environment commonly presents to that particular species in
its ecological niche. For example, Clark’s nutcrackers (birds
that cache food) are able to remember where they have stored
thousands of edible items (Kamil & Clements, 1990), a per-
formance that humans would be hard-pressed to match.
The fourth factor that stimulated an interest in the study
of basic learning was a practical one. Researchers such as
Thorndike (1949) and Guthrie (1938) were particularly con-
cerned with identifying principles that might be applied in
our schools and toward other needs of our society. Surely this
goal has been fulfilled at least in part, as can be seen for
example in contemporary use of effective procedures for
behavior modification.
Obviously, the human-versus-animal question (third fac-
tor listed) required that nonhuman animals be studied, but the
other questions in principle did not. However, animal sub-
jects were widely favored for two reasons. First, the behavior
of nonhuman subjects was assumed by some researchers to
be governed by the same basic laws that apply to human
behavior, but in a simpler form which made them more read-
ily observable. Although many researchers today accept the
assumption of evolutionary continuity, research has demon-
strated that the behavior of nonhumans is sometimes far from
simple. The second reason for studying learning in animals
has fared better. When seeking general laws of learning that
obtain across individuals, individual differences can be an
undesirable source of noise in one’s data. Animals permit
better control of irrelevant differences in genes and prior
experience, thereby reducing individual differences, than is
ethically or practically possible with humans.
The study of learning in animals within simple Pavlovian
situations (stimulus-stimulus learning) had many parallels
with the study of simple associative learning in humans that
was prevalent from the 1880s to the 1960s. The so-called
cognitive revolution that began in the 1960s largely ended
such research with humans and caused the study of basic
learning in animals to be viewed by some as irrelevant to our
understanding of human learning. The cognitive revolution
was driven largely by (a) a shift from trying to illuminate be-
havior with the assistance of hypothetical mental processes,
to trying to understand mental processes through the study of
behavior, and (b) the view that the simple tasks that were
being studied until that time told us little about learning and
memory in the real world (i.e., lacked ecological validity).
However, many of today’s cognitive psychologists often
return to the constructs that were initially developed before
the advent of the field now called cognitive psychology (e.g.,
McClelland, 1988). Of course, issues of ecological validity
are not to be dismissed lightly. The real question is whether
complex behavior in natural situations can better be under-
stood by reducing the behavior into components that obey the
laws of basic learning, or whether a more molar approach
will be more successful. Science would probably best be
served by our pursuing both approaches. Clearly, the ap-
proach of this chapter is reductionist. Representative of the
potential successes that might be achieved through applica-
tion of the laws of basic learning, originally identified in the
confines of the sterile laboratory, are a number of quasi-
naturalistic studies of seemingly functional behaviors. Some
examples are provided by Domjan’s studies of how Pavlov-
ian conditioning improves the reproductive success of
Japanese quail (reviewed in Domjan & Hollis, 1988),
Kamil’s studies of how the laws of learning facilitate the
feeding systems of different species of birds (reviewed in
Kamil, 1983), and Timberlake’s studies of how different
components of rats’ behavior, each governed by general laws
of learning, are organized to yield functional feeding behav-
ior in quasi-naturalistic settings (reviewed in Timberlake &
Lucas, 1989).
Although this chapter focuses on the content of learning
and the conditions that favor its occurrence and expression
rather than the function of learning, it is important to empha-
size that the capacity for learning evolved because it enhances
an animal’s biological fitness (reviewed in Shettleworth,
1998).The vast majority of instances of learning are clearly
functional.However, there are many documented cases in
which specific instances of learned behavior are detrimental
to the well-being of an organism (e.g., Breland & Breland,
1961; Gwinn, 1949). Typically, these instances arise in situa-
tions with contingencies contrary to those prevailing in the
animal’s natural habitat or inconsistent with its past expe-
rience (see this chapter’s section entitled “Predispositions:
Genetic and Experiential”). An increased understanding of
when learning will result in dysfunctional behavior is cur-
rently contributing to contemporary efforts to design im-
proved forms of behavior therapy.
This chapter selectively reviews research on both Pavlovian
(i.e., stimulus-stimulus) and instrumental (response-stimulus)
learning. In many respects, an organism’s response may be
functionally similar to a discrete stimulus, as demonstrated
by the fact that most phenomena identified in Pavlovian condi-
tioning have instrumental counterparts. However, one impor-
tant difference is that Pavlovian research has generally studied
qualitative relationships (e.g., whether the frequency or mag-
nitude of an acquired response increases or decreases with a
specific treatment). In contrast, much instrumental research