Network dynamics underlying alterations in apparent object size

Area of Science:

• Neuroscience
• Visual Perception
• Cognitive Psychology

Background:

• The Ebbinghaus illusion, where context circles alter perceived target size, involves both early and high-level visual processing.
• The precise interaction between these visual regions in generating the illusion remains incompletely understood.

Purpose of the Study:

• To investigate the neural network mechanisms underlying the Ebbinghaus illusion.
• To explore how manipulating attention affects the neural processing of illusory size perception.

Main Methods:

• Utilized functional magnetic resonance imaging (fMRI) to measure brain activity.
• Employed dynamic causal modeling (DCM) to analyze effective connectivity within neural networks.
• Manipulated participants' focus of attention on specific illusory configurations.

Main Results:

• Behavioral data confirmed the Ebbinghaus illusion.
• fMRI activity in the extrastriate cortex correlated with perceived size (larger activation for apparently larger circles).
• Reduced self-inhibition in the extrastriate cortex and increased feedback connectivity from the precuneus to the extrastriate cortex were observed.

Conclusions:

• Apparent object size representation is modulated by feedback projections from higher-level to lower-level visual areas.
• Top-down signaling plays a critical role in conscious visual perception and the generation of visual illusions like the Ebbinghaus effect.