BINOCULAR DISPARITY DEMONSTRATION
A technique that allows individuals to monitor their own physiological processes so they can learn to control them.
Biofeedback originated with the field of psychophysiology, which measures physiological responses as a way of studying human behavior. Types of behavior that may be studied in this way range from basic emotional responses to higher cognitive functions. Today, biofeedback is also associated with behavioral medicine, which combines behavioral and biomedical science in both clinical and research settings. In biofeedback training, the monitoring of physiological responses is performed for therapeutic instead of (or in addition to) investigative
BINOCULAR DISPARITY DEMONSTRATION
This simple experiment demonstrates binocular disparity. Hold a pencil about 12 inches (30 cm) from your face. With one eye closed, align the pencil with the edge of a doorway, window, or other vertical line in the room. Close the eye, open the other, and observe the position of the pencil: it will have jumped. Binocular disparity describes this phenomenon of different images of the pencil in each eye.
purposes. Biofeedback has been applied with success to a variety of clinical problems, ranging from migraine headaches to hypertension.
The technique provides people with continuous information about physiological processes of which they are normally unaware, such as blood pressure or heart rate. Through special equipment, these processes are recorded, and the information is relayed back to the person through a changing tone or meter reading. With practice, people learn strategies that enable them to achieve voluntary control over the processes involved. For example, persons trying to control their blood pressure levels may see a light flash whenever the pressure drops below a certain level. They may then try to remember and analyze what their thoughts or emotions were at that moment and deliberately repeat them to keep the pressure level low. Initially, they may simply be asked to try and keep the light flashing for as long as possible and given verbal reinforcement for their efforts.
The biofeedback training may continue for several days or weeks, with the subjects trying to keep the light flashing for longer periods in subsequent sessions. Eventually they will need to produce the desired response without electronic feedback, a goal which can be accomplished through various methods. They may practice the learned response at the end of the training session or at home between sessions. There can also be random trials without feedback during the sessions. An alternate strategy is the gradual and systematic removal of the feedback signal during the training sessions over a period of time. After the initial training is completed, subjects may return to the biofeedback facility to assess their retention of the skills they have learned or for additional training.
Biofeedback training has been used in treating a number of different clinical problems. Monitoring of patients' heart rates has been used with some success to help people suffering from heartbeat irregularities, including premature ventricular contractions (PVCs) and tachycardia, while hypertensive individuals have been
able to control high blood pressure through the use of biofeedback. Clinicians have been particularly successful in their use of neuromuscular feedback to treat complaints arising from tension in specific muscles or muscle groups. Tension headaches have been alleviated through the reduction of frontalis (forehead) tension, and relaxation of the face and neck muscles has been helpful to stutterers. Feedback from muscle groups has been helpful in the rehabilitation of stroke patients and other persons with neuromuscular disorders such as foot drop. These patients may be unable to relax or contract muscles at will, and biofeedback can make them aware of small, otherwise imperceptible changes in the desired direction and allow them to repeat and eventually increase such changes.
In addition to its alleviation of physical complaints, neuromuscular biofeedback has been an effective tool in the treatment of chronic anxiety, even when it has resisted psychotherapy and medication. By learning deep muscle relaxation, anxious patients, including those suffering from related conditions such as insomnia, have seen a reduction in their symptoms. Even for patients who have been able to achieve relaxation through other means, such as meditation or progressive relaxation, biofeedback can be a valuable supplementary technique that offers special advantages, such as allowing a therapist to track closely the points at which a patient tenses up and try to learn what thoughts are associated with the tension. Biofeedback-induced relaxation of forehead muscles has also been effective in treating asthma.
Another type of biofeedback involves the monitoring of brain activity through electroencephalographs (EEGs). A reduction of seizures in epileptics has been reported through biofeedback techniques involving EEG activity near the sensorimotor cortex, known as sensory motor rhythm. Brain wave activity has also been of interest in connection with alpha waves, which are thought to characterize a desirable state of relaxed alertness. Patients have been taught to increase their alpha rhythms in three or four 30-minute conditioning sessions.
Andreassi, John L. Psychophysiology: Human Behavior and Physiological Response. New York: Oxford University Press, 1980.
Beatty, J., and H. Legewie, eds. Biofeedback and Behavior. New York: Plenum Press, 1977.
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