PSYC 2330 Chapter Notes - Chapter 2: Startle Response, Supernormal Stimulus, Habituation
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Chapter 2: Elicited Behavior, Habituation, and Sensitization
- Is behavior totally flexible or is it subject to constraints set by the organism’s
o Locke (empiricist) favoured the view that experience and learning
can shape behavior in virtually any direction.
o Descartes (nativist) believed in innate contents of the mind (the
impact of learning is constrained by previous existing behavior
- Neuroscientists today favour more of the nativist approach, saying that
behavior is not infinitely flexible, to move in any way the trainer may push it,
but rather organisms are born with pre-existing behavior systems and
tendencies that set limits on how learning occurs and what the impact of
learning can be.
The Nature of Elicited Behavior
- All animals react to the events in their environment.
The Concept of Reflex
- I.e. a loud noise causes a startle reaction, a light puff of air directed at the
cornea makes the eye blink, and a tap just below the knee causes the leg to
- A reflex involves two closely related events: an eliciting stimulus and a
o The response and the stimulus are linked.
o A response rarely occurs in the absence of the stimulus.
- The relation between a stimulus and a response is a consequence of the
organization of the nervous system.
- In vertebrates, simple reflexes are mediated by three neurons.
o The environmental reflex activates a sensory neuron (afferent
neuron), which transmits the sensory message to the spinal cord.
o The neural impulses are relayed to the motor neuron (efferent
neuron), which activates muscles involved in the reflex response.
o Sensory and motor neurons are not directly in communication; rather
the impulses are relayed through at least one interneuron.
o This restricted wiring results in a particular reflex response elicited
only by a restricted set of stimuli.
o All these neurons together form the reflex arc.
- The respiratory occlusion reflex is stimulated by a reduction of air flow to the
baby, which can be caused by a cloth covering the baby’s face, or
accumulation of mucus in the nasal. In response the baby’s first reaction is to
pull her head back or even crying.
- The availability of milk in the breast is determined by the milk-letdown-
o Triggered by the infant’s suckling behavior. Or time cues such as time
of day or the baby crying when hungry.
Modal Action Patterns
- Response sequences, such as those involved in infant feeding, that are typical
of a particular species are referred to as modal action patterns (MAPs).
o Species-typical modal action patterns have been identified in many
aspects of animal behavior, including sexual behavior, territorial
defense, aggression and prey capture.
o I.e. Ringdoves begin their sexual behavior with a courtship interaction
that culminates in the selection of a nest site and the cooperative
construction of the nest by the male and female.
- An important feature of modal action patterns is that the threshold from
eliciting such behavior varies.
o The same stimulus can have wide variety of different effects
depending on the physiological state of the animal and its recent
o I.e. a male Stickleback will not court a female who is ready to lay eggs
until he has completed building the nest. And after the female has
deposited her eggs, the male will chase her away rather than court her
as he did earlier.
o These sexual and territorial responses will only occur when
environmental cues induce physiological changes that are
characteristic of the breeding season in both males and females.
Eliciting Stimuli for Modal Action Patterns
- The stimulus responsible for a modal action pattern can be more difficult to
isolate if the response occurs in the course of complex social interactions.
o I.e. (herring-gull chick) to get fed the chick has to peck the parent’s
beak to stimulate the parent to regurgitate. But what stimulates the
chick’s pecking response?
o Pecking by the chicks may be elicited by the color, shape, or length of
the parent’s bill, the noises the parent makes, the head movements of
the parent, or some other stimulus. From studies, researchers found
that the parent gull model had to be a long, thin, moving object that
was pointed downward and had a contrasting red patch near the tip.
o The specific features that are required to elicit a certain behavior
(pecking) are called, the sign stimulus (releasing stimulus) for this
o Once a sign stimulus has been identified, it can be exaggerated to elicit
an especially vigorous response, called a supernormal stimulus.
- Sign stimulus also plays a major role in the control of human behavior.
o Responding effectively to danger has been critical in the evolutionary
history of all animals, including human beings.
Those that did not respond accordingly did not pass their
genes on to future generations.
o Therefore, traumatic events have come to elicit strong defensive
modal action patterns.
The Sequential Organization of Behavior
- Responses do not occur in isolation of one another, rather, individual actions
are organized into functionally effective behavior sequences.
o I.e. to obtain food, a squirrel has to take a look around for potential
food sources, such as a pecan tree with nuts. Then it climbs the tree
and reaches for one of the nuts. After obtaining the nut, it cracks the
shell, extracts the meat, and chews and swallows.
o All motivated behavior involves systematically organized sequences
o Ethologists called early components of a behavior sequence
appetitive behavior and the end components consummatory
Consummatory = completion of a species typical response
Appetitive = serve to bring the organism into contact with the
stimuli that will release the consummatory behavior.
i.e. hitting and biting an opponent are actions that consummate
Appetitive behavior (i.e. preparing food) usually differs across
cultures, while consummatory behavior (chewing and
swallowing food) is usually the same regardless of culture.
o Learning theorists are becoming increasingly aware of the importance
of considering natural behavior sequences, and have expanded on the
appetitive and consummatory distinction made by early ethologists.
o In considering how animals obtain food, for example, it is now
common to characterize the foraging response sequence as starting
with a general search mode, followed by a focal search mode, and
ending with a food handling and ingestion mode.
Effects of Repeated Stimulation
- Contrary to Descartes, elicited behavior is not invariant.
- Alterations in the nature of elicited behavior often occur simply as a result of
repeated presentations of eliciting stimulus.
Salivation and Hedonic Ratings of Taste in People
- The taste of food elicits salivation as a reflex response.
All animals react to the events in their environment. I. e. a loud noise causes a startle reaction, a light puff of air directed at the cornea makes the eye blink, and a tap just below the knee causes the leg to kick. A reflex involves two closely related events: an eliciting stimulus and a corresponding response: the response and the stimulus are linked, a response rarely occurs in the absence of the stimulus. The relation between a stimulus and a response is a consequence of the organization of the nervous system. The respiratory occlusion reflex is stimulated by a reduction of air flow to the baby, which can be caused by a cloth covering the baby"s face, or accumulation of mucus in the nasal. In response the baby"s first reaction is to pull her head back or even crying. The availability of milk in the breast is determined by the milk-letdown- reflex: triggered by the infant"s suckling behavior.