Exploring the response code in a compatibility effect between physical size and left/right responses: The hand is...

Area of Science:

• Cognitive Psychology
• Neuroscience
• Human-Computer Interaction

Background:

• The spatial-size association of response codes (SSARC) effect describes improved performance when left-hand responses are made to small stimuli and right-hand responses to large stimuli.
• Existing research suggests a link between spatial coding and response selection, but the precise nature of this coding remains debated.
• Understanding the basis of SSARC effect is crucial for theories of magnitude representation and sensorimotor control.

Purpose of the Study:

• To investigate the underlying response coding mechanisms responsible for the spatial-size association of response codes (SSARC) effect.
• To determine whether response coding is primarily based on anatomical body position or external spatial location.
• To explore the influence of effector-body relationship on the SSARC effect.

Main Methods:

• Comparison of the SSARC effect using response selection between hands versus between fingers of a single hand.
• Investigation of the SSARC effect with parallel versus crossed arm configurations.
• Utilizing both keypress and reaching tasks to differentiate between external spatial position and effector-based coding.

Main Results:

• The SSARC effect was observed when selecting between hands but not between fingers, indicating body midline-based coding.
• The effect was present with parallel arms but not crossed arms, suggesting contributions from both effector anatomy and external position.
• In a reaching task, the SSARC effect tracked the arms, favoring an effector-based (anatomical) coding over external spatial position.

Conclusions:

• The findings strongly support an anatomically or body-based coding system for the SSARC effect.
• These results challenge the notion of a generalized magnitude system using a common external spatial metric.
• The study suggests that response codes underlying the SSARC effect are categorical rather than continuous.