Quantification of visual masking, a phenomenon of visual perception which occurs when the visibility of one image, called a target, is reduced by the presence of another, called a mask. Timing arrangements include forward masking, backward masking, and simultaneous masking. Spatial arrangements include pattern masking and metacontrast. Visual masking deficits are potential schizophrenia endophenotypes. The trait is visual masking measurement (EFO_0803378).