Biomedical subjects

C L Shupert

Publications and source records attributed to C L Shupert.

22 records · Page 2Linked to original sources

PubMed1982

Autokinesis and peripheral stimuli: implications for fixational stability.

The reduction in autokinesis of a fixated stimulus was determined as a function of the eccentricity of an identical second stimulus. When the stimuli were separated by 1 deg, autokinesis was reduced by approximately 50% but with increasing separation the attenuation was diminished. The results are interpreted in terms of fixational stability models of autokinesis. It is suggested that autokinesis as well as other examples of apparent movement result from fixational instability.

Adult↗

PubMedDate not supplied

Components of postural dyscontrol in the elderly: a review.

The concept of a generalized aging effect on a generalized balance mechanism is discussed, and an alternative, multicomponent approach to understanding the heterogeneity of postural dyscontrol in the elderly is presented. Neural sensorimotor components of normal postural control mechanisms are identified and discussed. The effects of Parkinson's disease, hemiplegia, cerebellar degeneration, peripheral vestibular loss, and other disorders on the components of postural control are summarized. Quantitative posturography is advocated to detect preclinical manifestation of multiple musculoskeletal and neuromuscular pathologies and reduced compensatory abilities in posturally unstable elderly adults.

Aged↗

PubMedDate not supplied

Hip sway associated with vestibulopathy.

We identify a population of patients with vestibular complaints who show excessive hip sway and center of gravity movement during clinical balance testing. To determine the postural control strategy used by these patients, the body movement and muscle activation patterns of 9 patients responding to backward support surface translations were studied. Patients' responses were compared to those of normal subjects tested both under the same conditions and while using hip sway to balance across a narrow beam. Unlike normal subjects responding to translations of a flat support surface, all patients showed hip movement patterns that kinematically resembled the movements of normal subjects balancing across a beam. Although all patients showed the same body movement patterns, they showed two different muscle activation patterns, neither of which was similar to those of normal subjects responding to flat support surface translations. Four patients showed bursts in abdominal and/or quadriceps muscles characteristic of active hip flexion to move the center of mass, although the timing of these bursts was variable. The remaining 5 patients showed minimal activation of any proximal muscles, suggesting a failure to control upper body motion resulting from activation of ankle muscles. To determine whether the excessive hip sway observed in these patients could be a voluntary response to platform translation, the patients' responses were compared to those of a second group of normal subjects voluntarily responding to backward support surface translations with hip sway. Unlike the patients, all normal subjects responding voluntarily consistently activated abdominal muscles slightly later than ankle muscles. It is therefore unlikely that the patients' responses to platform translations were simply voluntary responses. Thus, vestibular deficits can result in abnormally coordinated postural movement strategies that result in excessive hip sway.

Adolescent↗

PubMedDate not supplied

Effects of vestibular loss on head stabilization in response to head and body perturbations.

Control of head position during postural responses is important to facilitate both the interpretation of vestibular signals and the stabilization of gaze. In these experiments, we compared head stabilization for two different postural tasks: 1) in response to perturbations at the head, and 2) in response to perturbations induced at the support surface, which perturb both body and head position. To determine whether normal vestibular function is necessary for head stabilization in these two tasks, responses to forward and backward mechanical perturbations of the head and body were compared for 13 normal subjects and 4 patients with profound bilateral vestibular loss (two with vestibular loss in adulthood and two in infancy). Normal subjects showed little neck muscle activity for body perturbations, but large, early activations in both neck extensors and flexors for head perturbations. In contrast, vestibular patients showed excessive neck muscle activation for body perturbations and reduced or absent neck muscle activity for head perturbations. Patients with vestibular loss in adulthood also showed increased head acceleration in response to both head and body perturbations, but patients with vestibular loss in infancy showed more normal head accelerations. For body perturbations, the differences in head acceleration between patients and normals were greater for later head acceleration peaks, indicating poor head control during the execution of the postural response. Trunk angle changes were also higher in the patients for forward body perturbations, indicating that poorer control of trunk position could have contributed to their poorer head stabilization. These results indicate that the vestibular system plays an important role in head and trunk stabilization for both head and body perturbations. However, the more normal head accelerations of the patients with infant vestibular loss also indicate that other mechanisms, possibly involving neck reflexes, can at least partially substitute for the vestibular system to provide head and trunk stabilization.

Adolescent↗