Habituation and Sensitization

Type of psychology: Learning
Field of study: Biological influences on learning
Habituation, a form of behavior modification, is a decrease in behavioral response
that results from repeated presentation of a stimulus. Sensitization is a heightened behavioral
response that results from a stronger stimulus.
Key concepts
• adaptation
• innate
• learning
• neuron
• neurotransmitter
• opponent process theory
• stimulus
• synapse
Habituation and sensitization are the two most fundamental and widespread
forms of learning in the animal kingdom. According to ethologists,
learning is any modification in behavior that results from previous experience,
in some way involves the nervous system, and is not caused by development,
fatigue, or injury. More advanced forms of learning include association,
perceptual or programmed learning, and insight. The two simplest
(nonassociative) forms of learning are habituation and sensitization. These
two processes can be characterized as behavioral modifications that result
from repeated presentation of simple environmental stimuli.
Habituation is a decrease in response to repeated presentation of a stimulus—
an environmental cue that can potentially modify an animal’s behavior
via its nervous system. One of the most widely cited examples of this kind of
learning involves the startle response exhibited by nestling birds in response
to potential predators such as hawks. A young duck, for example, will exhibit
an innate startle response whenever a hawk-shaped model or silhouette is
passed overhead.With repeated presentation of the model, however, the intensity
of the bird’s response will decline as the animal becomes habituated,
or learns that the stimulus bears no immediate significance.
Common throughout the animal kingdom and even among some groups
of protozoans, habituation is important for preventing repeated responses
to irrelevant environmental stimuli that could otherwise overwhelm an organism’s
senses and interfere with other critical tasks. In the case of a nestling
bird, there is a clear advantage to an alarmresponse in the presence of a
potential predator; however, a continued fixed response would result in an
unnecessary expenditure of energy and distraction from other important
activities such as feeding.
In identifying a habituation response, it is necessary to distinguish between true habituation and sensory adaptation and fatigue. These latter two
phenomena involve a waning in responsiveness that is caused by temporary
insensitivity of sense organs or by muscle fatigue and thus are not considered
forms of learning. In contrast, habituation results in a drop in responsiveness
even though the nervous system is fully capable of detecting a signal
and eliciting a muscle response.
In contrast to habituation, sensitization is the heightened sensitivity (or
hypersensitivity) that results from initial or repeated exposure to a strong
stimulus. Examples of sensitization include the increased sensitivity of humans
to soft sounds following exposure to a loud, startling noise such as a
gunshot, or the increased responsiveness and sensitivity of a laboratory animal
to mild (usually irrelevant) tactile stimulation after an electric shock.
Sensitization increases an organism’s awareness and responsiveness to a variety
of environmental stimuli, thereby preparing it for potentially dangerous
situations.