Habituation

Behavior is often categorized into two fundamental forms: respondent and operant behavior. Respondent behavior is often called elicited behavior because it occurs in reaction to events or stimuli in the environment and is demonstrable in all animals with a nervous system. Respondent behavior includes reflexes (i.e., sucking in an infant when its mother's nipple is presented) and more complex responses such as feeding or reproductive behaviors that are elicited by multiple stimuli in the environment.

Habituation is considered to be an example of the most basic change in behavior that results from experience (i.e., learning). Habituation is defined as a diminution or reduction in responding after repeated presentations of an unconditioned environmental stimulus, and is differentiated from extinction, which involves a reduction in responding to conditioned stimuli. Habituation helps to channel behavioral responses, potentially affected by a barrage of stimuli, by organizing these responses in relation to the most relevant environmental influences. Although thought to be mediated at the level of the shortest neural pathway that connects the sensory apparatus to the muscles involved in making a response (i.e., the reflex arc), habituation is often distinguished from reduced responding as a result of the sense organs becoming temporarily insensitive to stimulation or from muscles becoming incapacitated by fatigue.

The intensity of the eliciting stimulus and the frequency of its presentation affect habituation. In general, the weaker the intensity of the eliciting stimulus and the more frequently an eliciting stimulus is presented, the sooner the organism will habituate a response (i.e., learn not to respond). Habituation is also considered to be “stimulus specific” in that even [Page 878]a minor change in the characteristics of the eliciting stimulus will evoke a response of full strength.

Two types of habituation have been proposed to operate in different experimental conditions. A long-lasting form of habituation occurs when the eliciting stimulus is presented after long pauses (i.e., once daily). The response to the eliciting stimulus gradually becomes smaller in magnitude but is not completely suppressed. When the learning condition includes frequent presentation of the same eliciting stimulus (i.e., every 5 seconds), the response quickly diminishes and is eliminated. This form is often referred to as short-lasting habituation.

As a real-world example of habituation, consider a typical family with two parents and a year-old baby boy named Jack. Russell, the father, had suffered from allergies his whole life and had developed an extremely loud sneeze that has been reportedly heard by neighbors two doors down when it occurs. For those unfamiliar with Russell's sneeze, when it occurred, they would exhibit a rather intense startle response, immediately followed by a strong urge to seek cover. The victims would typically require a few deep breaths to calm themselves down once again. The behaviorally oriented observer, victimized by Russell's explosivesounding sneeze, would soon recognize that he or she was the only person in the home exhibiting a pronounced startle response. Mary, Jack's mother, recalled that over the course of Jack's first few months of development, this same startle response would occur, followed by extended periods of crying. However, by the time Jack was 6 months old, he would barely interrupt his play when Russell sneezed. Jack had no longer reacted to his father's explosive-sounding sneeze and had habituated his startle response. It was as though Jack had learned that the loud sound was now generally an irrelevant stimulus in the environment.

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