What metacontrast masking tells us about the difference between foveal and peripheral vision

Metacontrast masking is a visual phenomenon in which the visibility of a target stimulus is reduced by the presentation of a subsequent non-overlapping mask. The strength of this effect depends on the temporal interval between the target and mask, known as stimulus onset asynchrony (SOA), and may reflect different visual processing mechanisms. The present study investigated metacontrast masking in central (foveal) and peripheral vision using a symmetry discrimination task. The aim was to examine whether masking patterns differ across visual field locations in accordance with the Central–Peripheral Dichotomy (CPD) hypothesis, which proposes stronger feedback processing in central vision and greater reliance on feedforward processing in peripheral vision. Participants completed experimental blocks in foveal and peripheral conditions (9° eccentricity). An adaptive procedure was used to adjust stimulus size across conditions, followed by a constant-stimulus task in which SOA varied across nine levels (0–200 ms), including a no-mask baseline condition. Results showed distinct masking patterns across visual field locations. Foveal vision produced an inverted U-shaped masking function, consistent with Type B masking, whereas peripheral vision showed strongest masking at short SOAs followed by a monotonic recovery pattern, consistent with Type A masking. These findings support the Central-Peripheral Dichotomy framework, suggesting that feedback mechanisms play a stronger role in foveal vision while peripheral vision relies more on feedforward processing.