Adaptation to altered support and visual conditions during stance: patients with vestibular deficits

Abstract

Patients whose deficits were limited to clinically well qualified vestibular disorders have been exposed to a number of altered support surface and visual environments while standing unsupported. A six-degrees-of-freedom platform employing movable support surfaces for each foot and a movable visual surround deprived patients of normal inputs derived from a fixed level support surface and from an immobile surround. Various tests employing EMG, force, and body movement recording identified quantitative changes in the patients' strategy for the relative weighting of proprioceptive, vestibular, and visual inputs. The most dramatic performance deficit of patients was their inability to suppress the influence of visual and proprioceptive inputs appropriately whenever motions of external surface disturbed the orientation information provided by these inputs. Thus, the more mildly afflicted patients experienced instability not so much because of the loss of vestibular inputs directly to posture but because of their inappropriate responses to proprioceptive inputs and vision. Discussion is centered on the role of vestibular input as an internal reference system for orientation about which adaptive changes in proprioceptive and visual inputs are made.

Reliability of postural control measures in children and young adolescents

“…Appropriate postural control is necessary to maintain an upright position and to maintain balance during most daily life activities; furthermore, it is the fundamental prerequisite for the motor development of children. Postural control requires the organization and integration of somatosensory, visual and vestibular inputs by the central nervous system and the motor control process involved in executing musculoskeletal responses that keep the body within its limits of stability [1]. children's balance control is less developed as compared to adults and postural stability improves progressively with age from childhood to adulthood [2][3][4][5][6][7][8][9][10][11].…”

Effect of treadmill gait training on static and functional balance in children with cerebral palsy: a randomized controlled trial

“…It is the complex ability of an individual to maintain the center of the gravity of the body over the support base 2 , when an individual is standing still (static balance), in motion (dynamic, functional balance), preparing to perform a movement or preparing to end a movement 1 . Postural control depends on the delicate integration of vision, vestibular and proprioceptive sensations, commands from the central nervous system and neuromuscular responses, particularly muscle strength and reaction time 3,4 . The quantification of displacement of the center of pressure through a stabilometric analysis is often used for the assessment of static balance (stability in a static position) 5 and the Berg Balance Scale 6 is used for the assessment of functional balance (postural stability during the performance of functional motor activities).…”

Direct perception of global invariants is not a fruitful notion

“…In such cases, the patterns in different arrays are said to conflict with one another (e.g., Bushnell & Weinberger 1987;Harris 1965;McGurk & MacDonald 1976;Nashner et al 1982); we refer to this as input conflict (Stoffregen & Riccio 1991). 4 Consider driving a car at constant velocity.…”

“…It is widely believed that there is erroneous or illusory perception of self-motion. To underscore the importance of the concept of perceptual error, Dichgans and Brandt (1978, p. 755) began their chapter with these words: "The sensation of self motion is a common visual illusion"; this interpreta- tion has been accepted generally (e.g., Howard 1982;Lee & Lishman 1975;Nashner et al 1982;Wertheim 1994). In these cases the error may be with the experimenter's assumption of an "absolute" referent for motion, and not with participants' percepts (cf.…”

“…Consider stance on a platform that can rotate around an axis parallel to the ankle joint (e.g., Nashner et al 1982). When the platform is stationary relative to the direction of balance, ankle rotation will have a fixed relation to head displacement, so that somatosensory and vestibular stimulation will be redundant.…”