Backward masking has several meanings.The original meaning of the term, in psychoacoustics, refers to temporal masking of quiet sounds that occur moments before a louder sound.A similar meaning, in use in cognitive psychology, refers to a phenomenon wherein presenting one visual stimulus (a "mask" or "masking stimulus") immediately after another brief (≤ 50 ms) "target" visual stimulus leads to a failure to consciously perceive the first stimulus.