Fear Motivation 43(Jacobs & LoLordo, 1980). These findings suggest that stim-
ulus selection in the laboratory reflects phylogenetic influ-
ences on stimulus selection in the species’ natural niche.
Innate Fear Stimuli
Learned fear stimuli require that an animal have previous ex-
perience with the stimuli to recognize the potential threat. In
contrast, innate fear stimuli are those stimuli that can be iden-
tified as potentially threatening without previous experience.
Animals display these responses without any specific training
experience.
It is difficult to develop unambiguous criteria that classify
innate fear stimuli. For instance, an unlearned fear stimulus
could be defined as a stimulus that elicits defensive behaviors
during its first presentation. With this definition a cat may be
considered an unlearned fear stimulus because laboratory-
reared rats exhibit robust defensive behaviors during their
first encounter with the predator. This behavior suggests that
the rodent’s genome retains information to detect certain in-
nate stimuli and provokes appropriate defensive reactions
(Blanchard & Blanchard, 1972). However, defensive reac-
tions to a cat could also be due to learning. In this alternative
account some aspect of the cat’s movement is the aversive
stimulus, and the rat exhibits defensive behaviors because it
is in an environment that has been paired with an aversive
stimulus. Thus, the rat freezes in the presence of the cat only
because its movement has been paired with other features of
the cat and not because the cat itself is an innately aversive
stimulus. This interpretation is supported by the observation
that a moving cat, dog, or inanimate card can trigger freezing
in the rat, although the sound, smell, or sight of a dead cat
does not (Blanchard, Mast, & Blanchard, 1975).
Also, the fact that a defensive response follows the
first presentation of a stimulus is not sufficient to classify
that stimulus as an innate releaser of fear. This is nicely ill-
ustrated by the analysis of electric shock. Fear responses
such as freezing, defecation, and analgesia follow the first
presentation of shock. However, shock per se does not un-
conditionally provoke these responses. Instead, it rapidly
and immediately conditions fear to the contextual cues pre-
sent before shock, and it is these conditional cues that elicit
the behaviors. Removing these cues before shock (Fanselow,
1986) or after shock (Fanselow, 1980) eliminates the re-
sponses. Similar patterns appear to exist (Blanchard,
Fukunaga, & Blanchard, 1976). Thus, we must exert consid-
erable caution before concluding that something is an innate
trigger of fear. This pattern also raises an important question
about the motivational properties of something like shock,
because although it supports conditioning of fear behavior, it
does not provoke fear itself. This pattern may be similar to
Balleine’s (1992) data, described earlier, suggesting that in-
centive properties of food must be learned.
Although prey species clearly react to predators in the
wild with elaborate defensive responses (Coss & Owings,
1978), these studies cannot control for the ontogenetic
history of the subject. Therefore, the best evidence for fear
reactions to a predator comes from laboratory studies with ro-
dents (Blanchard & Blanchard, 1972; Hirsch & Bolles, 1980;
Lester & Fanselow, 1985). The strongest evidence for phylo-
genetic influences on defensive behavior comes from a study
conducted by Hirsh and Bolles (1980). These investigators
trapped two subspecies of wild deer mice that live in distinct
regions of the state of Washington in the United States. Per-
omyscus maniculatus austeruscomes from the moist forest
regions in western Washington state, and Peromyscus manic-
ulatus gambelifrom an arid grassland region of eastern
Washington state. These animals were bred in the laboratory,
and their first generation of offspring were exposed to several
predators selected from the eastern and western regions.
When tested, P. m. gambeliboth survived more strikes and
survived longer when exposed to a predatory snake from its
niche compared to P. m. austerus. Thus,P. m. austeruswas
more vulnerable to attack by the predator alien to its niche.
Moreover, P. m. gambeliexhibited more fear responses to the
predator snake from its niche, compared to a nonpredatory
snake. Thus, P. m. gambeliwas able to discriminate between
two types of snake. These results suggest that the probability
of surviving an encounter with a predator is related to the
evolutionary selection pressure that that predator exerts on
the prey in their natural niche. Thus, animals adopt unlearned
or innate defensive strategies that allow them to cope with
predation in their niche.
Other observations suggest that a variety of species can in-
nately identify predators from their own niche (see Hirsch &
Bolles, 1980, for review). For example, rats exhibit robust
fear reactions to cats during their first encounter with the
predator, and this fear response does not seem to habituate
rapidly (Blanchard et al., 1998). However, recall from our
earlier discussion that cats are maximally fear provoking
when they are moving. Thus, it is difficult to ascribe the fear-
provoking ability to the cat “concept” when it is possible that
cat-like movements are essential for provoking fear in the rat
(Blanchard et al., 1975). Because a predator is a complex
stimulus, research is needed to isolate what aspects of it have
phylogenetic and ontogenetic fear-producing properties.
Bright light is another possible innate fear stimulus for ro-
dents; rodents avoid it consistently. Presumably, light signals