Two-dimensional static manipulation tasks: does force coordination depend on change of the tangential force...

Area of Science:

• Neuroscience
• Biomechanics
• Human Motor Control

Background:

• Grip force (GF) and tangential force (TF) coordination is crucial for object manipulation.
• Coordination is typically high in one-dimensional tasks, relying on feed-forward neural control.
• This coordination degrades in bidirectional tasks where TF direction switches.

Purpose of the Study:

• To investigate grip force and tangential force coordination in multi-dimensional manipulations.
• To test the hypothesis that coordination depends on the number of unidirectional and bidirectional orthogonal components of a two-dimensional TF.
• To explore the neural control mechanisms underlying force coordination in complex tasks.

Main Methods:

• Fourteen subjects performed two-dimensional tasks involving tracing circular TF patterns and orthogonal diameters.
• Subjects exerted static tangential forces while grip force was measured.
• Analysis focused on GF-TF correlations, GF gains, GF/TF ratio, and time lags.

Main Results:

• Unidirectional TF tasks showed significantly higher GF-TF coordination compared to bidirectional tasks.
• Circular tasks generally supported the hypothesis, with higher coordination linked to more unidirectional components.
• Prominent time lags between GF and TF were observed in circular tasks, suggesting feedback involvement.

Conclusions:

• Force coordination in bidirectional, multi-dimensional manipulations is influenced by changes in TF direction along orthogonal components.
• Observed time lags in circular tasks likely stem from sensory afferent activity, not visual feedback or task complexity.
• Findings suggest a shift towards feedback mechanisms in complex force coordination scenarios.