Anticipatory postural adjustments as a function of response complexity in simple reaction time tasks

Area of Science:

• Neuroscience
• Biomechanics
• Motor Control

Background:

• The central nervous system preplans postural responses, known as anticipatory postural adjustments (APAs), to ensure stability during complex movements.
• APAs are initiated with shorter latency when a startling acoustic stimulus is applied, confirming their preplanned nature.
• While task complexity affects limb movement reaction time (RT), its influence on APA dynamics remains unclear.

Purpose of the Study:

• To investigate whether task complexity modulates APA onset similarly to primary effector movements.
• To determine if APA dynamics are influenced by the sequencing requirements of varying task complexities.

Main Methods:

• 13 participants performed simple (1-target) and complex (2- or 3-target) arm movements while standing on a force plate.
• Reaction times for both arm movements and APAs were recorded.
• APA excursion velocities were analyzed in relation to movement complexity.

Main Results:

• Arm movement RTs were significantly faster in the simple condition compared to the most complex condition.
• APA RTs increased with task complexity, being longer for 3-target movements than for 1- or 2-target movements.
• APA excursion velocities scaled with movement complexity, increasing from simplest to most complex tasks.

Conclusions:

• Anticipatory postural adjustments are sensitive to task complexity.
• APA dynamics, including onset and velocity, are modulated by the preplanned requirements of upcoming movements.
• These findings reinforce the role of APAs in proactive postural stabilization for successful movement execution.