Distinct Contributions of Alpha and Beta Oscillations to Context-Dependent Visual Size Perception

Area of Science:

• Neuroscience
• Cognitive Psychology
• Visual Perception

Background:

• The Ebbinghaus illusion, a visual phenomenon, is attributed to contour interaction and size contrast mechanisms.
• The neural basis of these cognitive mechanisms underlying the Ebbinghaus illusion remains largely uninvestigated.

Purpose of the Study:

• To explore the neural underpinnings of contour interaction and size contrast in the Ebbinghaus illusion.
• To investigate how manipulating binocular depth affects the Ebbinghaus illusion and its neural correlates.

Main Methods:

• Introduced binocular depth cues into the Ebbinghaus illusion setup, varying the relative depth of the central target and surrounding inducers.
• Measured neural oscillations, specifically alpha-band (8-13 Hz) and beta-band (14-25 Hz) power, in response to the illusion under different depth conditions.
• Correlated changes in neural activity with the magnitude of the Ebbinghaus illusion effect.

Main Results:

• The Ebbinghaus illusion effect was significantly reduced when binocular depth cues were present, although the illusion persisted.
• Early alpha-band power (0-100 ms) at centroparietal sites decreased with larger perceived target size, regardless of depth, and was negatively correlated with the illusion effect.
• Late beta-band power (200-300 ms) over occipito-parietal regions increased with larger perceived target size in the no-depth condition, positively correlating with the illusion effect when depth effects were removed.

Conclusions:

• Neurophysiological evidence supports distinct neural mechanisms for the Ebbinghaus illusion: early alpha power is linked to low-level contour interaction, and late beta power is associated with high-level size contrast.
• Neural oscillations in different frequency bands dynamically support distinct aspects of visual processing, contributing to complex perceptual phenomena like the Ebbinghaus illusion.