Chapter 2 - Elicited Behavior, Habituation,
and Sensitization

Elicited behavior is behavior which happens in response to some environmental event. This chapter looks at changes in innate behaviors. Throughout the rest of the course, we will talk about changes in learned behavior.

The Nature of Elicited Behavior

You will see that the the term "reflex" typically refers to innate behaviors that are elicited by stimuli. This first section discusses the simple reflex arc, which consists of a sensory, or afferent, neuron, at least one interneuron, and a motor, or efferent, neuron.

Some types of reflexes can be quite complex and specific to individual species. These are then called modal action patterns (MAPs) or fixed action patterns (the more common, but less preferred name). These reflexes are elicited by sign stimuli, or releasing stimuli, in the environment, and many very cleverly designed experiments have been conducted to determine exactly what the sign stimulus is in any given situation. You would learn more about this in a course on comparative psychology, or ethology.

Effects of Repeated Stimulation

This section introduces the notion that even innate reflexes can be modified by experience. Repeated exposure to the eliciting stimulus can either decrease or increase the size of the response. The section is basically setting the stage for the next section.

The Concepts of Habituation and Sensitization

In general, habituation is a decrease in the size of an innate response to a stimulus resulting from exposure to the stimulus. Sensitization is an increase in the size of the response. We will talk about these processes in detail in class. Be sure to understand the distinction between habituation and sensory adaptation and response fatigue.

Habituation and sensitization are controlled by different mechanisms, as described in the dual-process theory. Habituation is a function of the S-R system, or changes in the neurons controlling the response, whereas sensitization is a function of the state system, or changes in the state of arousal of the organism. Most changes in behavior as a result of repeated exposure to the stimuli are a combination of the two systems.

Characteristics of Habituation and Sensitization

Understand the distinctions between short-term habituation and long-term habituation. The obvious difference is the durability of the habituation; habituation lasts either for a short time or a long time. Long-term habituation is what we typically think of as learning, because it represents a relatively stable and enduring change in behavior. These two types of habituation may be products of different neural mechanisms.

The descriptions of stimulus generalization and stimulus specificity of habituation are important and straightforward.

Dishabituation can occur when the animal's state of arousal is enhanced. If so, we see an increase in the response that had become habituated.

Changes in Complex Emotional Responses

This final section introduces an interesting theory about how emotional states that are elicited by stimuli can change as a result of repeated exposure to the stimuli. We will talk about this theory in class, discussing in detail the interactions of the a and b processes.