Anticipatory synergy adjustments: preparing a quick action in an unknown direction

Area of Science:

• Motor control
• Neuroscience
• Human-computer interaction

Background:

• Multi-finger actions require complex coordination.
• Visual feedback is crucial for motor adjustments.
• Anticipatory synergy adjustments (ASAs) are proposed feed-forward mechanisms.

Purpose of the Study:

• Investigate ASAs in multi-finger force control.
• Determine sensitivity of ASAs to timing and direction of visual feedback changes.
• Understand the role of ASAs in preparing for altered sensory information.

Main Methods:

• Subjects maintained force with four fingers.
• Visual feedback gain was unexpectedly altered (0.2x or 1.8x).
• Timing and direction of gain change were manipulated (known/unknown).
• Synergy index measured pre- and post-force correction.

Main Results:

• ASAs initiated earlier (250-300 ms) when gain change timing was known.
• ASAs initiated later (<100 ms) when timing was unknown.
• Gain change direction did not affect ASA timing.
• ASA magnitude was larger when gain change direction was unknown.

Conclusions:

• ASAs are a key feed-forward mechanism for preparing actions.
• ASAs can adapt to altered sensory information even without knowing the exact change.
• Motor control exhibits sophisticated multi-finger synergy adjustments.
• Findings support central back-coupling and referent configuration hypotheses.