Illusion effects on grasping are temporally constant not dynamic

Area of Science:

• Cognitive Psychology
• Motor Control
• Visual Perception

Background:

• The Ebbinghaus illusion demonstrates how surrounding context influences perceived object size.
• Previous research suggested visual illusions could be corrected during the late stages of grasping movements.
• This correction was thought to support specific models of action planning and control.

Purpose of the Study:

• To investigate whether the Ebbinghaus illusion's effect on grasping is corrected during the late phases of movement.
• To re-evaluate previous findings and identify potential artifacts in earlier studies.
• To refine understanding of motor control theories.

Main Methods:

• Participants (N=52 no-vision, N=48 full-vision) performed grasping movements towards a target.
• Grasp aperture was measured under different visual conditions.
• Statistical analyses were performed to identify movement corrections.

Main Results:

• Grasp aperture was not corrected for the Ebbinghaus illusion in either no-vision or full-vision conditions.
• Previous reports of correction were attributed to artifacts, including late time points and erroneous statistics.
• The central evidence for the Glover and Dixon (2001a) planning-control model was invalidated.

Conclusions:

• The Ebbinghaus illusion does not influence the late phases of grasping movements.
• Methodological artifacts in prior studies led to incorrect conclusions about motor correction.
• Classic online-control theories remain viable, while specific planning-control models are challenged.