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Feedforward Processing in Early Visual Cortex Underlies the Ebbinghaus Illusion
Song Zhao1, Yi Fang1, Mengdie Zhai1
1Department of Psychology, School of Education, Soochow University.
Cognitive Science
|August 3, 2026
Summary
The Ebbinghaus size illusion, impacting visual perception, originates in the primary visual cortex (V1) during the initial feedforward processing stage. This research provides strong evidence for early visual cortex involvement in this size illusion.
Area of Science:
- Neuroscience
- Visual Perception
- Cognitive Psychology
Background:
- The Ebbinghaus illusion demonstrates how surrounding context influences perceived size.
- Previous research implicated low-level occipital regions, including V1, in this illusion.
- The precise timing of V1's involvement (feedforward vs. feedback) remained unclear.
Purpose of the Study:
- To determine if the Ebbinghaus illusion is processed at the feedforward stage in the visual cortex.
- To investigate the role of the primary visual cortex (V1) in the early stages of this illusion.
Main Methods:
- Event-related potentials (ERPs) were recorded from human participants viewing the Ebbinghaus illusion.
- Specific analysis focused on the C1 component, an index of V1 activity.
- Granger causality analysis assessed information flow between visual processing areas.
Main Results:
- A significant, illusion-specific lateralization of the C1 component was observed, indicating V1 activity.
- This C1 lateralization was replicated and not attributable to attentional bias.
- Granger causality confirmed a feedforward information transfer from V1 to extrastriate areas.
Conclusions:
- The findings provide strong evidence that the Ebbinghaus illusion is initiated at the feedforward stage of cortical visual processing.
- This supports the contour interaction theory's prediction of early V1 involvement.
- The study clarifies the temporal dynamics of visual processing in size perception illusions.
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