Repetition effects in action planning reflect effector- but not hemisphere-specific coding

Area of Science:

• Cognitive Neuroscience
• Motor Control
• Human Movement Science

Background:

• Action planning is influenced by recent and future action states.
• Repetition effects, such as faster response times (RTs) with repeated hand use, suggest effector-specific processing.
• However, the role of hemisphere-specific processing versus effector-specific processing remains debated.

Purpose of the Study:

• To dissociate effector-specific from hemisphere-specific repetition effects in action planning.
• To investigate whether using the same limb or the same hemisphere influences action initiation speed.

Main Methods:

• Participants performed sequential movements using hands and feet.
• Movement directions were specified using egocentric or allocentric reference frames.
• Response times for initiating the second action were measured.

Main Results:

• Successive actions were initiated faster when the same limb executed both movements.
• This 'same-limb advantage' persisted regardless of movement direction (egocentric or allocentric).
• No advantage was observed when using different limbs controlled by the same hemisphere (e.g., left foot-left hand).

Conclusions:

• Repetition effects in action planning are genuinely effector-specific.
• Neural populations encoding effector-specific action plans exhibit persistent changes.
• Findings support a model where action planning involves distinct neural representations for different limbs.