Postural and Manual Control During Constrained Tasks

Hoda Salsabili, Purdue University

Abstract

The concurrent control of both standing and manual tasks are sophisticated since redundant, mechanically linked degrees of freedom (DOF) must be coordinated by a control strategy in a manner that affords completion of both tasks (Berret, Chiovetto, Nori, & Pozzo, 2011). In previous studies, a flexible control strategy was typically adopted and presented as the best behavior in the young adults in a task with only a manual task challenge (Kim et al., 2012) or postural task demand (Reisman et al., 2002). For the first study, we argued the flexible control strategy is the byproduct of experimental design with minimal challenge. When both manual and postural tasks are challenging, the motor system may adopt a less flexible control strategy to coordinate joint angles. We aimed in the first study to show that a less flexible control strategy can adapt to the challenges of a postural manual task in young adults. Twelve healthy participants (25 ± 4.2 years) performed a fitting task that required a small block to be transported, fitted, and held in a small or large opening for five seconds while standing on a narrow or wide surface. In addition to the uncontrolled manifold (UCM) analysis (variability spanned in the UCM space (Vucm), orthogonal space (Vort), and coordination metric (DVz) for hand and CoM control, we determined the hand and CoM standard deviation (SD) on 20 error-free trials (no block contact with the opening and no tilting of the surface). We found higher CoM and hand SD as well as invariant CoM and hand Vucm imposed by the narrow surface, which resulted in a reduction of joint-angle variability (less flexible control strategy) while holding a block in the small or large opening. The smaller CoM and hand SD, and greater Vucm, suggested a more flexible control strategy was adopted when standing on a wide surface and attempting the action of fitting the block to the small opening. The strength of the control strategy remained high across these conditions (high DVz). We concluded that a flexible control strategy is not a ubiquitous movement strategy in young adults (at both levels of coordinating joint angles and the variability of end effectors). We argued that the postural constraint (i.e., standing on the narrow surface) is the driving factor in the control strategy throughout a postural manual task. The immobilization of joints and muscle co-contraction were discussed that facilitated the postural task priority. The consequence of postural constraint (i.e., falling) appeared to increase the notion of postural control and explained our findings. Thus, in the first study, we inferred the consequences associated with the tasks (falling and losing precision) might induce higher priority for one task. The direct examination of the task prioritization was investigated in the second study In the second study, we examined task prioritization in a postural manual task. This specific paradigm was chosen because both manual and postural tasks can have consequences if they are not performed properly. In previous studies, posture is often considered to have priority over the concurrent performance of other tasks (Bloem et al., 2002). However, both postural and manual tasks can have consequences if they are executed poorly.

Degree

Ph.D.

Advisors

Haddad, Purdue University.

Subject Area

Aging|Gerontology|Neurosciences|Optics

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