Time-to-contact measures capture modulations in posture based on the precision demands of a manual task.

The integration between posture and manual control while performing fitting tasks of varying difficulty was investigated. Participants fit a block into either a small (high precision) or large (low precision) opening while standing on a force plate. Postural time-to-contact was used to quantify changes in posture that occurred during the fitting movement. Results suggest that posture became more stabilized when fitting through the small opening (postural time-to-contact values were higher) compared to when fitting through the large opening. Additionally, when fitting through the small opening, individuals modulated sway based on the instantaneous demands of the task. Specifically, time-to-contact was lower towards the end of a fitting movement (as the individual prepared to fit the block through the opening) compared to the beginning of the movement. These results suggest that the dynamics of postural sway are constantly changing based on the constraints of a concurrent task.

[1]  B. Vereijken,et al.  Free(z)ing Degrees of Freedom in Skill Acquisition , 1992 .

[2]  Jay Hertel,et al.  Deficits in time-to-boundary measures of postural control with chronic ankle instability. , 2007, Gait & posture.

[3]  David A. Winter,et al.  Anticipatory control of center of mass and joint stability during voluntary arm movement from a standing posture: interplay between active and passive control , 2002, Experimental Brain Research.

[4]  Keith Davids,et al.  Movement system variability , 2005 .

[5]  J. Gibson.  The Ecological Approach to Visual Perception , 1979 .

[6]  Karl M. Newell,et al.  Variability and Motor Control , 1993 .

[7]  R. van Emmerik,et al.  Postural orientation: age-related changes in variability and time-to-boundary. , 2002, Human movement science.

[8]  M. Latash,et al.  Muscle synergies involved in shifting the center of pressure while making a first step , 2005, Experimental Brain Research.

[9]  Benoît G. Bardy,et al.  Postural coordination modes considered as emergent phenomena , 1999 .

[10]  M. Latash,et al.  Movement sway: changes in postural sway during voluntary shifts of the center of pressure , 2003, Experimental Brain Research.

[11]  Paul J. Stapley,et al.  Coordination between equilibrium and hand trajectories during whole body pointing movements , 2002, Experimental Brain Research.

[12]  Roger Bartlett,et al.  Movement Systems as Dynamical Systems , 2003, Sports medicine.

[13]  Karl M. Newell,et al.  Virtual Time-to-Collision and Human Postural Control. , 1997, Journal of motor behavior.

[14]  Joseph Hamill,et al.  Evaluation of time-to-contact measures for assessing postural stability. , 2006, Journal of applied biomechanics.

[15]  Richard E.A. van Emmerik,et al.  On the functional aspects of variability in postural control. , 2002 .

[16]  E. Gibson,et al.  An Ecological Approach to Perceptual Learning and Development , 2000 .

[17]  Karl M. Newell,et al.  Virtual time-to-contact of postural stability boundaries as a function of support surface compliance , 2007, Experimental Brain Research.

[18]  M T Turvey,et al.  Specificity of postural sway to the demands of a precision task. , 2000, Gait & posture.

[19]  Richard E. A. Van Emmerik,et al.  Developmental changes in the dynamical structure of postural sway during a precision fitting task , 2008, Experimental Brain Research.

[20]  Joseph Hamill,et al.  Clinical Relevance of Coordination Variability , 2005 .

[21]  P. N. Kugler,et al.  The informational support for upright stance , 1985, Behavioral and Brain Sciences.

[22]  M. Latash,et al.  Muscle synergies during shifts of the center of pressure by standing persons , 2003, Experimental Brain Research.

[23]  Randy J. Pagulayan,et al.  Postural stabilization of looking. , 1999 .

[24]  Suvobrata Mitra,et al.  Effects of explicit sway-minimization on postural--suprapostural dual-task performance. , 2004, Human movement science.

[25]  Steven L. Wolf,et al.  The Effect of Tai Chi Quan and Computerized Balance Training on Postural Stability in Older Subjects , 1997 .