Habit outweighs planning in grasp selection for object manipulation

Area of Science:

• Motor control
• Human movement science
• Cognitive neuroscience

Background:

• Object-directed grasping movements are adapted based on intended interactions.
• The control mechanisms for grasp adjustment (habitual vs. goal-directed) remain unclear.

Purpose of the Study:

• To investigate whether grasp adjustments for object manipulation are primarily habitual or goal-directed.
• To determine the relative contribution of habitual and goal-directed processes in grasp selection.

Main Methods:

• Participants performed a dial rotation task with varying numbers of rotation steps (one, two, or three).
• Grasp posture and end-state arm posture were analyzed during practice and transfer trials.
• Contingency between grasp orientation and arm end-state was manipulated.

Main Results:

• Participants in multi-step rotation groups adapted their grasps to avoid extreme arm postures.
• When performing single-step rotations, participants' grasps reflected previously learned multi-step adjustments.
• The carry-over of learned grasp adjustments was not complete, indicating a mixed control system.

Conclusions:

• Grasp adjustment for object manipulation is controlled by a combination of habitual and goal-directed processes.
• Habitual processes contribute approximately twice as much as goal-directed processes to grasp selection.
• This suggests a significant role for learned, automatic responses in everyday object interaction.