Illusions as a tool to study the coding of pointing movements.

Area of Science:

• Visual perception and psychophysics
• Motor control and visuomotor adaptation

Background:

• Pictorial illusions can influence judgments of visual attributes.
• Pointing tasks can utilize either vector coding (direction/distance) or position coding (final location).

Purpose of the Study:

• To investigate which visual attributes guide pointing movements under the influence of the Brentano illusion.
• To determine how varying visual feedback (hand/target visibility) affects reliance on different coding strategies.

Main Methods:

• Utilized the Brentano illusion, a length distortion illusion.
• Tested pointing movements in various conditions manipulating hand and stimulus visibility.
• Analyzed pointing trajectories to differentiate between position and vector coding contributions.

Main Results:

• The Brentano illusion influenced pointing movements along the illusion's axis but not perpendicular to it.
• Increased illusion influence was observed when the hand and/or target were not visible during movement.
• Pointing strategies showed varying relative contributions of position and vector coding depending on visual conditions.

Conclusions:

• Pointing movements are guided by a combination of position and vector coding, with position coding often dominating.
• Visual feedback significantly modulates the reliance on different coding strategies during visually guided pointing.
• The Brentano illusion's impact on pointing is dependent on the specific visual attributes engaged by the task and feedback conditions.