Ebbinghaus figures that deceive the eye do not necessarily deceive the hand

Area of Science:

• Cognitive Psychology
• Neuroscience
• Human Motor Control

Background:

• The visual stream dissociation hypothesis proposes separate brain pathways for perception and action.
• Previous studies on visual illusions like the Ebbinghaus figure yielded inconclusive results regarding their effect on motor control ('deceiving the eye but not the hand').

Purpose of the Study:

• To investigate the specific impact of the Ebbinghaus illusion parameters on repetitive aiming movements.
• To determine if motor control is similarly deceived by size illusions as perception is.

Main Methods:

• Participants performed a Fitts' task using Ebbinghaus figures as targets.
• Systematic manipulation of target size, target-context distance, and context circle size was employed.
• Movement dynamics during repetitive aiming were analyzed.

Main Results:

• Movement was significantly affected by the size of the context circles in the Ebbinghaus figure.
• Unlike perceptual judgments, motor control was not influenced by target size or target-context distance.
• This effect was prominent during the approach phase of the movement, irrespective of movement dynamics.

Conclusions:

• Motor control utilizes different visual information than perception, even when perceptual illusions are present.
• The findings support the dissociation between vision-for-perception and vision-for-action, with context size being a key variable for action.
• This research reconciles contradictory findings by highlighting distinct informational bases for perceptual and motor responses to visual stimuli.