Biomedical subjects

J Jeka

Publications and source records attributed to J Jeka.

3 recordsLinked to original sources

PubMed2000

Multisensory information for human postural control: integrating touch and vision.

Despite extensive research on the influence of visual, vestibular and somatosensory information on human postural control, it remains unclear how these sensory channels are fused for self-orientation. The focus of the present study was to test whether a linear additive model could account for the fusion of touch and vision for postural control. We simultaneously manipulated visual and somatosensory (touch) stimuli in five conditions of single- and multisensory stimulation. The visual stimulus was a display of random dots projected onto a screen in front of the standing subject. The somatosensory stimulus was a rigid plate which subjects contacted lightly (<1 N of force) with their right index fingertip. In each condition, one sensory stimulus oscillated (dynamic) in the medial-lateral direction while the other stimulus was either dynamic, static or absent. The results qualitatively supported five predictions of the linear additive model in that the patterns of gain and variability across conditions were consistent with model predictions. However, a strict quantitative comparison revealed significant deviations from model predictions, indicating that the sensory fusion process clearly has nonlinear aspects. We suggest that the sensory fusion process behaved in an approximately linear fashion because the experimental paradigm tested postural control very close to the equilibrium point of vertical upright.

Adult↗

PubMed1999

Precision contact of the fingertip reduces postural sway of individuals with bilateral vestibular loss.

Contact of the hand with a stationary surface attenuates postural sway in normal individuals even when the level of force applied is mechanically inadequate to dampen body motion. We studied whether subjects without vestibular function would be able to substitute contact cues from the hand for their lost labyrinthine function and be able to balance as well as normal subjects in the dark without finger contact. We also studied the relative contribution of sight of the test chamber to the two groups. Subjects attempted to maintain a tandem Romberg stance for 25 s under three levels of fingertip contact: no contact; light-touch contact, up to 1 N (approximately 100 g) force; and unrestricted contact force. Both eyes open and eyes closed conditions were evaluated. Without contact, none of the vestibular loss subjects could stand for more than a few seconds in the dark without falling; all the normals could. The vestibular loss subjects were significantly more stable in the dark with light touch of the index finger than the normal subjects in the dark without touch. They also swayed less in the dark with light touch than when permitted sight of the test chamber without touch, and less with sight and touch than just sight. The normal subjects swayed less in the dark with touch than without, and less with sight and touch than sight alone. These findings show that during quiet stance light touch of the index finger with a stationary surface can be as effective or even more so than vestibular function for minimizing postural sway.

Aged↗

PubMed1998

Position and velocity coupling of postural sway to somatosensory drive.

Light touch contact of a fingertip to a stationary surface provides orientation information that enhances control of upright stance. Slight changes in contact force at the fingertip lead to sensory cues about the direction of body sway, allowing attenuation of sway. In the present study, the coupling of postural sway to a moving contact surface was investigated in detail. Head, center of mass, and center of pressure displacement were measured as the contact surface moved rhythmically at 0.1, 0.2, 0.4, 0.6, and 0.8 Hz. Stimulus amplitude decreased with frequency to maintain peak velocity constant across frequency. Head and body sway were highly coherent with contact surface motion at all frequencies except 0.8 Hz, where a drop-off in coherence was observed. Mean frequency of head and body sway matched the driving frequency </=0.4 Hz. At higher frequencies, non-1:1 coupling was evident. The phase of body sway relative to the touch plate averaged 20-30 degrees at 0.1-Hz drive and decreased approximately linearly to -130 degrees at 0.8-Hz drive. System gain was approximately 1 across frequency. The large phase lags observed cannot be accounted for with velocity coupling alone but indicate that body sway also was coupled to the position of the touch plate. Fitting of a linear second-order model to the data suggests that postural control parameters are not fixed but adapt to the moving frame of reference. Moreover, coupling to both position and velocity suggest that a spatial reference frame is defined by the somatosensory system.

Adaptation, Physiological↗