|
||||||||
|
|
|
|
|
|
|
|
|
 |
Research Mission Research in the Ashton Graybiel Spatial Orientation Laboratory spans the full spectrum of topics including sensory motor adaptation, motion sickness, perception of human body orientation and the effects of varying force environments on the control of movement, posture, and balance. The Graybiel Laboratory’s experimental program is designed to advance our effort to develop a predictive model of human vestibular orientation, posture, and neural control. Novel human subject experiments are performed to further our understanding of the human body and brain. By researching and examining a wide range of topics we can help to explain and solve practical problems in aeronautics, astronautics, and clinical populations.
|
| Current Research | |
We have previously shown that Coriolis and centripetal forces result when an arm movement is performed during trunk rotation and that these forces produce large trajectory deviations during passive, constant velocity trunk rotation but do not affect movement trajectory during normal, voluntary turn and reach (T&R) movements (Pigeon et al. 2003a,b). Recently, we studied the accuracy of T&R movements when the generated Coriolis forces were augmented by having the subjects hold a 454g object in their hand. The consequence of holding the weight is to magnify the effect of the Coriolis force by increasing the effective inertial mass of the arm. We were also interested in whether there would be equal performance for the left and right arm. The results indicated that compensations for forthcoming Coriolis force variations take into account the dynamic properties of the body and of external objects, as well as the planned velocities of the torso and arm (Pigeon et al. 2008). References: Pigeon P, Bortolami SB, DiZio P, Lackner JR (2003a) Coordinated turn and reach movements. I. Anticipatory compensation for self-generated Coriolis and interaction torques. J. Neurophysiol. 89(1): 276-289. Pigeon P, Bortolami SB, DiZio P, Lackner JR (2003b) Coordinated turn and reach movements. II. Planning in an external frame of reference. J. Neurophysiol. 89(1): 290-303. Pigeon P, Lackner JR, DiZio P (2008) Immediate compensation for variations in self-generated Coriolis forces related to body dynamics and carried objects. Soc Neurosci Abstr, 2008. |
|
| Back to Top | |
|
|
|
We have carried out extensive studies demonstrating that light touch of the hand at mechanically non-supportive force levels attenuates body sway and enhances postural control under a wide variety of circumstances in normal subjects and in patients with bilateral vestibular loss Subjects were tested under six randomly presented experimental conditions involving vision (V) of the test chamber or darkness (D) with either no touch (N), the arms passively by the sides, or precision touch (T), contact of the right index finger at less than 1N (@100 grams) of force, or force contact (F), as much force as desired. Touch forces were measured with full bridge, temperature compensating, semiconductor strain gauges. We calculated the mean sway amplitude (MSA) of the center of foot pressure. Subjects typically applied about 40 grams of force in the touch conditions (DT, VT). Mechanically, 40 grams of force applied at the fingertip can attenuate sway at most by 4% (Holden, Ventura, Lackner, 1987, 1994), but touch contact (DT) reduced sway by 50-60% relative to the no-contact control condition (DN). Forty grams at the fingertip corresponds to the maximal dynamic sensitivity range of the finger’s cutaneous receptors (Westling & Johansson, 1987). This force level thus allows optimal resolution of contact force vectors that provide information about body sway. Clapp and Wing (1999) repeated this study with subjects in a feet side by side stance and replicated our results. Thus, precision touch greatly attenuates body sway and is even more effective than vision by itself. When vision is allowed, precision touch further attenuates sway. Other findings from our Precision Touch experiments include: 1) Precision touch decreases leg muscle EMG activity. Less energy is required to maintain balance when precision touch information about sway is present because sway is detected and corrected earlier. 2) Precision touch contact stabilizes congenitally blind subjects. This means postural destabilization arising from aberrant leg muscle or neck muscle activity can be suppressed by precision touch. 3)Precision touch stabilizes individuals with bilateral vestibular loss. Light touch of the index finger with a stationary surface allows labyrinthine defective subjects to balance as accurately as normal subjects References: Holden M, Ventura J, Lackner JR. Influence of light touch from the hand on postural sway. Society for Neuroscience Abstracts 13(1):348, 1987 Holden M, Ventura J, Lackner JR. Stabilization of posture by precision contact of the index finger, J Vestib. Res. 4:285-301, 1994. Jeka JJ and Lackner JR. The role of haptic cues from rough and slippery surfaces on human postural control. Exp Brain Res 103: 267-276, 1995 Jeka JJ, Easton RD, Bentzen BL, Lackner JR. Haptic cues for orientation and postural control in sighted and blind individuals. Perception & Psychophysics, 58(3):409-423, 1996. Jeka JJ, Lackner JR. Fingertip contact influences human postural control. Exp Brain Res, 100(3): 495-502, 1994. Lackner JR, Rabin E, DiZio P. Stabilization of posture by precision touch of the index finger with rigid and flexible filaments. Exp Brain Res, 139: 454-464, 2001. Lackner JR, DiZio P, Jeka JJ, Horak F, Krebs D, Rabin E. Precision contact of the fingertip reduces postural sway of individuals with bilateral vestibular loss. Exp Brain Res, 126: 459-466, 1999. Rabin E, Bortolami SB, DiZio P, Lackner JR. Haptic stabilization of posture: Changes in arm proprioception and cutaneous feedback for different arm orientations. J Neurophysiol. 82: 3541-3549, 1999 Rabin E, DiZio P, Lackner JR. Time course of haptic stabilization of posture. Exp Brain Res. 170:122-126, 2006 Soeda K, DiZio P, Lackner JR. Balance in a rotating artificial gravity environment. Exp Brain Res, 148: 266-271, 2003 |
|
| Back to Top | |
|
|
|
The Hold and Release Paradigm is a technique designed to study the link between the biomechanics of the human body and the physiology, by evoking a transition from quiet standing to a perturbed stance and recovery. In the hold and release paradigm, subjects actively resist a force applied to their sternum; this force is then suddenly released. The force release provides a planar, pulsatile perturbation that is small enough to evoke postural oscillations from which subjects can recover. Subjects were tested standing on a force plate with feet side-by-side as they attempted to stand as straight and still as possible. The experimenter then pushed steadily against the subject’s sternum with a dynamometer, ~15 N of force, while the subject actively resisted and maintained an erect posture. The experimenter suddenly and without warning withdrew the dynamometer. The subject then propelled forward by the offset between the CoP and the CoM and attempted to regain balance as quickly as possible without shifting or lifting his/her feet or stepping. An Optotrak motion analysis system (Northern Digital, Inc.) monitored infrared emitting diodes (IREDs) attached to the subject’s ankle, knee, hip, and shoulder. A Kistler force plate recorded the A-P CoP. An instrumented dynamometer used to apply the holding force to the subject’s chest provided a signal that indicated the precise moment of release. Data channels were sampled at 120 Hz. With the data collected, our overall goal is to develop a quantitative model, with concrete links to biomechanics and physiology. Continuing research includes conducting the experiment in normal and novel environments. Reference: Bortolami SB, DiZio PA, Rabin E, Lackner JR. Analysis of human postural responses to recoverable falls. Experimental Brain Research, 151: 387-404, 2003. |
|
| Back to Top | |
|
|
|
When multi-joint reaching movements are made within a rotating reference frame, additional interaction torques are generated in the form of Coriolis forces. Coriolis forces are a function of the cross product of the angular rotation of the reference frame, the linear velocity of the arm relative to the reference frame, and the effective mass of the arm. When subjects reach forward during counter-clockwise rotation, there is a rightward Coriolis force on their arm relative to their torso. We have found that subjects seated at the center of a fully enclosed slow rotation room turning at constant velocity (10 rpm) initially make large reaching errors when pointing to targets. Both the paths and the endpoints of their movements are deflected in the direction of the transient Coriolis forces generated by their movements. The Coriolis forces are absent prior to and after the end of a reaching movement, because they are dependent on the linear velocity of the arm relative to the rotating reference frame. When allowed to make repeated movements, the subjects rapidly adapt to the Coriolis forces generated by their movements and again reach in straight paths accurately to the targets (Lackner & DiZio, 1994). Post-rotation, the motor adaptation carries over, resulting in aftereffects of opposite sign. Labyrinthine-defective subjects show patterns of movement disruption similar to those of normal subjects, and they also exhibit trajectory adaptation and post-rotation aftereffects (DiZio & Lackner, 2001). In our rotating room experiments, subjects always feel stationary while reaching. There are no visual cues about rotation because the room is enclosed. The semicircular canals cease signaling rotation after about a minute of rotation at constant velocity. A subject seated over the rotation axis at 10 rpm is only exposed to sub-threshold centripetal forces. In this situation, in the absence of voluntary movements, maintained counterclockwise rotation is perceptually identical to being stationary. The subjects feel stationary and at first do not compensate for the Coriolis force generated on their arm when they make a reach. This pattern indicates that when subjects do not veridically register their body rotation with respect to external space, they do not initially compensate for the Coriolis forces generated during their reaches. Compensation is an automatic, non-conscious process that requires repeated reaches for complete recalibration to occur. Reference: Lackner, J.R., DiZio, P. Rapid adaptation to Coriolis force perturbations of arm trajectory. J. Neurophysiol., 72(1): 299-313, 1994. |
|
| Back to Top | |
|
|
|
|
