This is a schematic of the masking task. For each trial participants are shown a target letter (row one, column one), followed by a brief inter-stimulus-interval (row one, column two), followed by the mask (row one, column three). Participants then verbally indicate which of four letter options was just presented (row 1, column 4). If the participant is correct (as in trial 1) at the next trial the contrast of the target is reduced (row 2, column 1). This procedure continues until the participant commits and error (as in row 3, column 4) and then the contrast of the target letter is increased (row 4, column 1). This procedure continues until the accuracy criterion is reached.