Abstract
Forward masking (e.g., paracontrast) is a type of visual masking in which the perceived visibility of a target is modulated by a preceding mask. Although this masking paradigm has been used in vision research, we have a limited understanding of neural correlates. In particular, the ERP components (event-related potentials) associated with this paradigm have not been systematically investigated. Accordingly, we designed two separate studies based on paracontrast masking. In both studies, we recorded EEG (Electroencephalography) activity while observers performed a contour discrimination task on the target. Besides mask-target onset timing (SOA), we manipulated mask-to-target (M/T) contrast ratio in the first study and the contrast polarity of the mask (same vs. opposite polarities) in the second study. The behavioral performance values (reflecting the perceived visibility of the target) indicated significant dependency on the SOA values and revealed strong inhibitions due to mask in the short SOA range. Moreover, the magnitude of these brief inhibitions was significantly modulated by the M/T contrast ratio and mask polarity. The EEG analyses revealed nonlinear mask-target interactions in the P1, N1, and late component ranges that are significantly dependent on SOA. More importantly, the analyses indicated that the M/T contrast ratio significantly modulated the interactions in the P1 and N1 component ranges. To sum up, our findings revealed neural correlates of inhibitory processes involved in paracontrast masking and provide important insights into the ERP components associated with forward masking. They also contribute to the understanding of cortical dynamics underlying perceived visibility.