Habituation and Sensitization Habituation refers to decreases in responses by repeated presentation of a known stimulus; sensitization is the opposite and refers to increased responses, with both types of change resulting from previous experience. Both occur in many situations, but always require repeated exposure to a stimulus. They are necessary in designing control procedures in classical conditioning and have a role in operant conditioning (Domjan, 2003). Habituation is the only non-associative form of learning and considered the simplest. Habituation is a process that allows individuals the ability to filter out large amounts of sensory stimuli that bombard us continually, allowing an individual the ability to focus their attention to more relevant information. The dual-process theory of habituation and sensitization proposes that both habituation and sensitization processes are not "mutually exclusive" and that both may be activated at the same time with the underlying outcome dependent on the strength of either process. In other words, both processes compete to control behavior (Domjan, 2003). The theory suggests habituation and sensitization processes "occur in different parts of the nervous system" (Domjan, 2003). According to this theory, habituation processes occur in the "S-R system." The S-R system provides the "shortest neural path" connecting the sense organs activated by the eliciting stimulus and the muscles related to the response. This process is defined as a "reflex arc" (Domjan, 2003). The continuous presentation of a sensory stimulus activates the S-R system causing the habituation effect. Habituation is one of several ways to change dog’s behavior. According to Burch and Bailey (1999), habituation can be called "adaptation" because the subject animal begins to adapt having less reaction to a given stimulus after being repeatedly exposed several times. Using the reflexive startle response as an example, a gun dog might show a decrease in startle response after repeated gunfire exposure. However, habituation can be temporary if exposure to the eliciting stimulus is not maintained at sufficient levels.

Sensory Adaptation and Response Fatigue Compared to Habituation

The most important characteristic of habituation is a declining response to a previously elicited stimulus. There are other reasons why a response to a particular stimulus would decline other than habituation. In order to understand the difference, we must reconsider reflexes.

Sensory or afferent neurons that send messages to the brain may become temporarily "insensitive" to stimulation due to a blinding light or temporary hearing loss after attending a rock concert. These decreases in sensitivity are referred to as sensory adaptation.

The motor or efferent neurons responsible for sending messages away from the brain and spinal cord and controlling muscles may become ineffective due to response fatigue. Both sensory adaptation and response fatigue impede response, acting outside the nervous system in "sense organs and muscles," and for this reason are different from habituation (Domjan, 2003).

It is assumed neurophysiological changes prevent or assist communication of the sensory neurons to the motor neurons through habituation or sensitization. Even though an organism is able to respond to a stimulus using the appropriate muscles they fail to respond due to habituation, which apparently blocks the sensory neural impulses to the motor neurons (Domjan, 2003).

Sensory adaptation is distinguished from habituation when it can be determined that habituation is "response-specific" and "an organism may stop responding to a stimulus in one aspect of its behavior while continuing to respond to the stimulus in other ways" says Domjan (2003).

Sensitization

Sensitization is the opposite of habituation in that it produces increases in responsiveness, rather than decreasing responses. However, like habituation sensitization does not usually have lasting effects. According to Domjan (2003), "in all response systems the duration of sensitization effects is determined by the intensity of the sensitizing stimulus" with the greater the stimulus the greater responsiveness and the more intense the stimuli, the longer the duration the sensitizing effects will persist.

The Dual-Process theory suggests sensitization processes take place in the "state system" (Domjan, 2003). This system is responsible for other parts of the nervous system, maintaining arousal levels, and activated by arousing stimuli and emotional experiences. Drugs "such as stimulants or depressants" are able to alter the state system changing levels of response. The highly emotional state of fear is controlled by the state system.

Applying a sensitization process to dog training might include relaxation training; establishing hierarchies of stimulus presentations beginning with the least intrusive, as we slowly increase the level of tolerance, at the same time applying counter-conditioning using a reinforcer. Understanding the short duration associated with a sensitization process, a fearful dog for example should be continually exposed to a previous fearful stimulus to maintain the newly established positive response and to generalize the behavior to multiply conditions.

Habituation and sensitization are respondent conditioning processes, and related to biology and reflexes and sometimes overlapped by operant learning. When working with dogs and fear issues, we are commonly working with respondent conditioning, because fear responses are reflexive changing one’s biological condition and reflected by increased heart rate and respiration. However, these responses may also be due to some type of operant learning experience, causing avoidance behavior associated with fear and anxiety.

Finally, both habituation and sensitization processes are limited in their application and only involve responses already in the animals behavioral repertoire and do not include "learning new responses or responses to new stimuli" and usually involve just one type of stimuli, according to Domjan (2003).

References

Burch, Mary R., & Bailey, Jon S. (1999). How Dogs Learn.
New York: Howell

Taflinger, M., & Wilkinson, J. (Eds.). (2003). The Principles of Learning and Behavior . (5th ed.).
CA: Wadsworth/Thompson

Reid, Pamela J. (1996). Excel-erated Learning .
CA: James & Kenneth

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