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Changing one's focus of attention alters the structure of movement variability
Abbigail L Fietzer1, Carolee J Winstein1, Kornelia Kulig1
1Division of Biokinesiology and Physical Therapy, University of Southern California, 1540 Alcazar St, CHP 155, Los Angeles, CA 90089, USA.
Abstract:
Substantial evidence supports the beneficial effect of an external (vs. internal) focus of attention on task performance during goal-directed movements. Counter-intuitively, an external focus has also been shown to increase joint-level movement variability.
Objective:
To determine whether shifting attentional focus can alter the structure of movement variability, thereby offering a probable mechanistic explanation for how adopting an external focus of attention might confer its benefits.
Methods:
Thirty-five healthy adults (age 23-55) performed unipedal hopping under three different attentional foci: natural (no directed focus), internal focus, and external focus. Uncontrolled manifold analysis was used to examine the structure of movement variability with respect to stabilization of leg orientation and vertical leg length during hopping. Takeoff/landing event bin and stance phase integrals of performance-irrelevant and performance-destabilizing variability were compared across focus conditions.
Results:
Accuracy of hopping in place improved with both external and internal foci compared to the natural condition (.004 ≤ p ≤ .035). External focus, to a greater degree than internal focus, destabilized leg orientation at takeoff and landing compared to the natural condition (.001 ≤ p ≤ .038). External focus increased - but internal focus decreased - leg length stabilization throughout stance compared to the natural condition (p < .001).
Conclusion:
External focus was superior to internal and natural focus conditions in terms of increasing flexibility within the system to orient the leg differently at takeoff and landing to compensate for unintentional drift during hopping. An external focus increased leg length stabilization in stance by preferentially increasing the subset of variability that explores multiple successful performance options. These results provide an understanding of the mechanism underlying external focus benefits - improving movement variability/coordination.