Dissociating size representation for action and for conscious judgment: Grasping visual illusions without apparent...

Area of Science:

• Cognitive Psychology
• Neuroscience
• Visual Perception

Background:

• Visual illusions highlight the brain's dual processing of sensory information.
• The Ebbinghaus/Titchener illusion shows conscious size misperceptions, while motor responses may use veridical size information.
• Previous research suggests factors beyond perceived size, like perceived obstacles, influence grip scaling.

Purpose of the Study:

• To investigate whether grip size scaling relies on veridical object size or perceived size influenced by visual illusions.
• To test the dual representation theory using a visual illusion that minimizes confounding factors like perceived obstacles.

Main Methods:

• Utilized the diagonal illusion to separate perceived length from actual size, avoiding confounding obstacle effects.
• Experiment 1: Assessed conscious length perception through direct comparisons.
• Experiment 2: Measured grip size scaling (finger-thumb span) based on perceived length.

Main Results:

• Grip size scaling consistently reflected the actual physical size of objects.
• Illusory effects significantly biased conscious perception of length in both direct comparisons and grip span estimations.
• Motor responses (grip scaling) remained veridical, supporting distinct unconscious representations.

Conclusions:

• The findings support the dual representation theory, indicating separate conscious and unconscious visual representations.
• Unconscious visuo-motor systems utilize veridical object size for actions like grip scaling, independent of conscious perceptual distortions.