Early suppression effect in human primary visual cortex during Kanizsa illusion processing: A magnetoencephalographic...

Area of Science:

• Neuroscience
• Visual Perception
• Computational Neuroscience

Background:

• Illusory contour (IC) detection primarily involves the lateral occipital complex.
• The role of the primary visual cortex (V1) in IC processing remains debated, with some evidence suggesting early suppression.
• Iso-oriented luminance borders, key to Kanizsa illusions, may cause surround suppression in V1, reducing initial responses.

Purpose of the Study:

• To investigate the existence, localization, and timing of early suppression effects from Kanizsa figures in the human brain.
• To test the hypothesis that V1 exhibits relative suppression to Kanizsa figures compared to control stimuli.

Main Methods:

• Used magnetoencephalography (MEG), sensitive to V1 and V2 activity, in adult participants under passive viewing conditions.
• Presented two sizes of visual stimuli (4.5° and 9.0°) to probe effects at different eccentricities.
• Analyzed data from the medial occipital area and occipital pole within a 40-120 ms time window post-stimulus onset, employing threshold-free cluster enhancement and permutation statistics.

Main Results:

• Detected a significant "inverted IC effect," characterized by relative suppression of brain responses to Kanizsa figures compared to control stimuli.
• The suppression effect was observed in the early visual processing stages (40-120 ms) within the V1 and V2 regions.
• The findings were consistent across different stimulus sizes and eccentricities.

Conclusions:

• The study confirms early relative suppression in V1 in response to Kanizsa figures, supporting the surround suppression hypothesis.
• This suppression is likely evoked by iso-oriented collinear borders and may relate to the principle of sparse coding.
• This early V1 mechanism is a crucial preliminary step for subsequent object contour detection.