Habituation is a psychological learning process where there is a gradual reduction of a behavioral response following repeated exposure to a stimulus. It occurs when an individual learns to tune out a stimulus that is neither harmful nor rewarding after determining that the stimulus is inconsequential. An example of this might involve a person who initially responds to a loud noise, but over time, learns to ignore it if the noise has no direct impact on them.
Desensitization, on the other hand, is a therapeutic technique aimed at reducing anxiety or fear associated with a particular stimulus or situation. The process involves controlled repeated exposure to the stimulus that elicits an unwanted response, with the goal of reducing the intensity of emotional reactions.
Desensitization often incorporates relaxation techniques and is progressively applied; it assumes that fear is learned and can, therefore, be unlearned through exposure. Both mechanisms entail a decrease in response, but while habituation does not necessarily require a systematic approach, desensitization is a structured process typically guided by a therapist or a structured program.
Principles of Habituation
When a stimuli is presented repeatedly, the response to it decreases. Habituation, a type of non-associative learning, is also suggested to be a type of implicit learning, as is frequent with repeatedly presented stimuli. This is congruent with the notion of habituation as a method, but in order to validate habituation as a process, additional qualities must be demonstrated.
There has also been evidence of spontaneous recovery. That is, a habitual response to a stimulus recovers (increases in amplitude) when a large period of time (hours, days, weeks) has passed between stimulus presentations.
Some habituation processes tend to result in a habituation period of many days or weeks. This is classified as long-term habituation. It lasts for an extended period of time (with little or no spontaneous recovery).
When spontaneous recovery tests are given frequently, “potentiation of habituation” occurs. In this phenomena, the decline in responding after spontaneous recovery accelerates with each test of spontaneous recovery. It was also found that increasing the frequency of stimulus presentation (i.e., shortening the interstimulus interval) speeds up habituation.
Habituation is important in psychiatry and psychopathology because a number of neuropsychiatric conditions, such as autism, schizophrenia, migraine, and Tourette’s, cause reductions in habituation to a wide range of simple and complex stimulus types.
Principles of Desensitization
Systematic desensitization is a procedure pioneered by psychologist Mary Cover Jones in the 1920’s that helps people unlearn phobias and fears. Later, psychiatrist Joseph Wolpe devised a method of creating a hierarchical list of anxiety-inducing stimuli in order of intensity, allowing individuals to adjust.
Although medication is available for people suffering from anxiety, fear, or phobias, empirical evidence suggests that desensitization has a high cure rate, especially in patients with depression or schizophrenia.
The client and therapist work together to create a hierarchical list of fears or phobias, starting with the least upsetting and progressing to the most frightening. The therapist and the phobic patient then develop a list of escalating exposure scenarios.
Second, the client is taught strategies for profound relaxation. This is continued until the hierarchy part no longer evokes worry or terror, and then the next scenario is shown.
The process is repeated until the client completes the hierarchy. It is impossible to feel both anxiety and relaxation at the same time, thus guiding the client into deep relaxation helps to reduce anxiety.
Systematic desensitization can then be accomplished by gradually approaching the frightened stimulus while remaining relaxed. Desensitization is most effective when people are directly exposed to the stimuli and situations they dread, thus anxiety-inducing stimuli are combined with inhibitory reactions.
This is accomplished either by having clients perform in real-life scenarios (vivo desensitization) or, if it is not practicable to directly carry out the steps of the hierarchy, by witnessing models performing the feared behavior (vicarious desensitization). Clients progress slowly up the hierarchy, repeating performances if needed, until the final item on the list is completed without fear or anxiety.
According to habituation theory, when exposure to a stimulus increases, the phobic subject’s response decreases. Empirical evidence suggests that in vivo exposure reduces general phobia reactions in those who have specific phobias. However, because habituation is reversible and temporary, evidence does not support it as an explanation for desensitization.
Neurological Aspects of Habituation and Desensitization
Nerve fatigue refers to a temporary decline in the ability of a neuron to respond to a stimulus after a period of repeated exposure. This phenomenon is a fundamental component of habituation, and it is distinct from neurological damage as it is reversible. The process occurs as the nervous system selectively filters out redundant information, which helps organisms focus on novel information in their environments.
The alterations in synaptic transmission that occur during habituation have been widely studied in the Aplysia gill and siphon withdrawal response. Habituation has been shown in almost every species of mammal, at least one species of plants (Mimosa pudica), and in isolated neuronally-differentiated cell-lines.
Desensitization can be associated with changes in receptor activity, particularly the NMDA (N-methyl-D-aspartate) receptors, which play a critical role in synaptic plasticity and memory formation. NMDA receptor antagonists can induce desensitization by preventing calcium influx into the neuron, thereby dampening the excitability of the neuron in response to subsequent stimuli. This process is more complex and involves not just a reduction in response but an alteration of the neural circuitry underlying the response.
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