44 Motivation
threat because rats are more visible in bright environments.
Thus, negative phototaxis may be an example of defensive
behavior. Walker and Davis (1997) reported that rats display
enhanced startle after they have been exposed to bright light.
These investigators suggested that bright light elicits fear
and that this light-enhanced startle is a manifestation of that
fear. Thus, this phenomenon resembles the fear-potentiated
startle procedure in which startle behavior is enhanced by the
presentation of learned fear stimuli (Davis, 1986).
Recent evidence has also suggested that predator odors
may act as innate releasers of defensive behavior. For exam-
ple, Wallace and Rosen (2000) reported that exposure to a
component of fox feces, trimethylthiazoline (TMT), elicits
freezing behavior in the rat. However, these results may be
related to the intensity of the odor and to the test chamber’s
small dimensions. What is needed in all these cases is a set of
criteria that unambiguously indicate that a stimulus is an in-
nate fear stimulus. We do not have these criteria yet, but we
know from the research with shock that a defensive response
following the first occurrence of a stimulus is not sufficient.
Observational Learning and Fear Stimuli
This third class of fear stimuli has been developed from stud-
ies on social interactions in monkeys. Lab-reared monkeys
normally do not exhibit fear reactions in the presence of a
snake, whereas wild-reared monkeys do (Mineka & Cook,
1988). However, the fear of snakes can be socially transmit-
ted by a phenomenon called observational learning.
In these experiments a lab-reared observer monkey can
view a wild-reared cohort as it interacts with an object. The
object may be a snake, a toy snake, or a flower. If the cohort
is interacting with a toy snake or a flower, the animal does not
exhibit any fear responses, such as fear grimacing or walking
away. When this same monkey interacts with the snake, it
will exhibit fear reactions. Interestingly, when an observer
monkey sees its cohort engaging in fear behaviors when it en-
counters the snake, the observer monkey will later display
fear responses to the snake. Mineka suggests that monkeys
can learn about threats by observing conspecifics interact
with threatening stimuli.
This phenomenon demonstrates a sophisticated means
to learn about threats. Notice that the monkey can learn
to fear the snake without direct experience with the snake.
This phenomenon is distinct from a typical Pavlovian fear-
conditioning session because the animal does not experience
the US directly. It learns fear of the snake through observation.
Regardless, observational learning shares selection processes
that are similar to standard Pavlovian learned fear, and mon-
keys readily learned fear to snakes, but not to flowers, through
observation. Thus, this type of fear may actually be a phylo-
genetically predisposed form of learning as well.Functional Behavior Systems Analysis of
Defensive BehaviorFear elicits defensive behavior in a myriad of species
(Edmunds, 1974). Each species has its own repertoire of de-
fensive behaviors, and similar species such as the rat and
hamster may react to a similar threat in very different ways.
But if a species has a number of defensive behaviors in its
repertoire, how does it select among them?
Throughout much of the twentieth century, the selection of
fear-motivated behavior was most commonly explained
with reinforcement principles. For example, Mowrer and
Lamoreaux (1946) suggested that animals learn to avoid fear-
provoking stimuli because the event ofnotreceiving an aver-
sive stimulus is reinforcing. Thus, rats learn to flee from
predators because the tendency to flee is strengthened by
negative reinforcement when they successfully avoid preda-
tion. Despite their popularity, however, theories like these
provide an inadequate account of fear-motivated behavior
(summarized in Bolles, 1975). Consequently, alternative
accounts that use a behavioral systems approach to explain
these behaviors have been developed. These explanations
acknowledge that different species may use distinct defensive
responses. These explanations of defensive behavior also
deemphasize the importance of reinforcement in response
production and emphasize the primacy of innate defensive
behaviors.
The first data that led to these behavioral systems explana-
tions came from Gibson (1952), who studied defensive
behavior in the goat. She demonstrated Pavlovian condition-
ing of the goat’s leg flexion response and noted that goats
performed many different behaviors such as running away,
turning around, and backing up after the shock was delivered.
Gibson concluded that leg flexion itself was not a defensive
reaction but that it was simply a common component of
the other behaviors that she observed. Thus, leg flexion in
the goat appears to be a component of several defensive
responses.
Akin to Gibson’s findings, Bolles (1970) proposed an
explanation of avoidance behavior known as the species-
specific defensive reaction (SSDR) hypothesis.This hypothe-
sis suggests that every species has its own repertoire of innate
defensive behaviors and that animals perform these behav-
iors unconditionally when they become afraid. For example,
a rat’s SSDRs include fleeing, freezing, fighting, and dark
preference. Thus, when a rat becomes afraid, it will perform
these defensive behaviors unconditionally; it does not learn