Planning to reach for an object changes how the reacher perceives it

Area of Science:

• Cognitive psychology
• Visual perception
• Action planning

Background:

• The Ebbinghaus illusion demonstrates how surrounding context influences perceived size.
• Previous research suggested distinct visual pathways for perception versus action.
• This distinction was based on reduced illusion effects during grasping.

Purpose of the Study:

• To investigate the Ebbinghaus illusion's impact on size judgments preceding different motor responses.
• To test the hypothesis of separate visual systems for perception and action.
• To explore the relationship between action planning and perceptual judgments.

Main Methods:

• Three experiments were conducted involving size judgments before verbal, grasping, or touch responses.
• Participants judged the size of a central circle (target) surrounded by other circles.
• The magnitude of the Ebbinghaus illusion was measured across different response conditions.

Main Results:

• The Ebbinghaus illusion's magnitude was similarly reduced for grasping and judgments preceding grasping.
• A comparable reduction in the illusion was observed before reaching to touch targets.
• The illusion's effect persisted in verbal judgments even when a touch task was anticipated.
• Reduced illusion effects from a prior grasping task carried over to subsequent verbal judgments.

Conclusions:

• Perceptual judgments and action planning are strongly interconnected.
• The findings challenge the strict separation of visual systems for perception and action.
• Action planning appears to influence, and be influenced by, perceptual size judgments.