The arrangement of stimuli used in Experiment 1. The arrangement is simplified graphically by illustrating all stimuli as squarely-ramped. In the two-interval forced-choice task (see text), one interval (randomly chosen on each trial) contains a 2-kHz 200-ms forward-masker which precedes a much briefer 2-kHz tone. As the latter tone’s presentation time post-masker increases, the intensity for its threshold detection decreases (dashed lines). In the other interval, no tone appears post-masker.