Biomedical subjects

L J Smart

Publications and source records attributed to L J Smart.

4 recordsLinked to original sources

PubMed2001

Postural dynamics: clinical and empirical implications.

OBJECTIVE: To provide a rationale for the examination of posture from a dynamic (behavioral) perspective and to relate the vertebral subluxation to postural instability and motion sickness via inefficiency. DATA COLLECTION: A manual search of available reference texts and a computer search of literature from Index Medicus, PsycINFO, and ISI Science Citation Index Expanded were collected with an emphasis on postural dynamics, vertebral subluxation, and motion sickness. RESULTS: Evidence linking behavioral and health research has emerged from the study of posture and postural dynamics. Studies examining the relation between postural control and motion sickness have shown that motion sickness is preceded and predicted by postural instability. Motion sickness is characterized by maladaptive response to unusual motion events. The symptoms are nonspecific and variable. Although the Postural Instability theory of motion sickness predicted that instability should precede sickness, it did not make any claims regarding the symptoms associated with it. Chiropractic literature has emphasized the effects of vertebral subluxation on neurologic dysfunction. Vertebral subluxation is a condition that is postulated to interfere with neurologic processes and may influence organ system function and general health. As in the case of motion sickness, symptoms are nonspecific and variable (and in some instances the person may have no symptoms). So what do these disorders have in common? In each instance the disruptions lead to inefficiency in the system. CONCLUSION: Given this potential commonality, we propose that some of the methods used by behavioral researchers to study postural dynamics may also be of great utility to health care practitioners and psychologists alike. Furthermore we propose that this link will provide a framework that will allow scientists to address seemingly intractable problems such as motion sickness or subluxation.

Biomechanical Phenomena↗

PubMed2000

Postural instability and motion sickness in a fixed-based flight simulator.

We evaluated the prediction that postural instability would precede the subjective symptoms of motion sickness in a fixed-base flight simulator. Participants sat in a cockpit in a video projection dome and were exposed to optical flow that oscillated in the roll axis with exposure durations typical of flight simulation. The frequencies of oscillation were those that characterize spontaneous postural sway during stance. Head motion was measured prior to and during exposure to imposed optical flow. Of 14 participants, 6 were classified as motion sick, either during or after exposure to the optical oscillation. Prior to the onset of subjective symptoms, head motion among participants who later became sick was significantly greater than among participants who did not become motion sick. We argue that the results support the postural instability theory of motion sickness. Actual or potential applications include the prevention or mitigation of motion sickness in virtual environments.

Adult↗

PubMed1998

Postural instability precedes motion sickness.

We evaluated the hypothesis that postural instability precedes the onset of motion sickness. Subjects standing in a "moving room" were exposed to nearly global oscillating optical flow. In the experimental condition, the optical oscillations were a complex sum-of-sines between 0.1 and 0.3 Hz, with an excursion of 1.8 cm. This optical motion was of such low frequency and magnitude that it was sometimes not noticed by subjects. However, in two experiments, exposure to the moving room produced significant increases in scores on a standard motion sickness questionnaire. In addition, approximately half of subjects reported motion sickness. Analysis of postural motion during exposure to the moving room revealed increases in postural sway before the onset of subjective motion sickness symptoms. This confirms a key prediction of the postural instability theory of motion sickness.

Adaptation, Physiological↗

PubMed1998

Self-induced motion sickness in unperturbed stance.

Motion sickness typically occurs when the body is subjected to externally imposed motions, but there are situations in which sickness occurs in the absence of imposed motion. We report a new and unanticipated instance of the latter. Subjects in a study of spontaneous standing postural sway sometimes reported dizziness and motion sickness. Reports of sickness were correlated with changes in postural sway. We consider possible implications of these findings for two current theories of motion sickness etiology: the sensory conflict theory and the postural instability theory.

Adaptation, Physiological↗