Stimuli.

<p>Schematic depiction of a trial. In a two-interval auditory intensity discrimination task, the two target tones (<i>T₁</i> and <i>T₂</i>) were combined with two forward maskers (<i>M₁</i> and <i>M₂</i>). All tone levels were independently and randomly perturbed. The gray horizontal lines show the mean levels for maskers (µM), standard (µ_S), and standard-plus-increment (µ_S+I). The level increment (µ_S+I−µ_S = 5 dB in this example trial) was individually selected for percent correct in the range from 70% to 85%. It was presented in either the first or the second interval with equal probability. The dotted rectangles depict the randomly selected tone levels in the example trial (<i>L</i>_M1 to <i>L</i>_T2).