Distribution of percent correct on the tone discrimination test for discriminators, nondiscriminators, and controls. Lower and upper limits for percent correct intervals: 50 ≤ X <52.5, 52.5 ≤ X <55, 55 ≤ X <57.5, 57.5 ≤ X <60, 60 ≤ X <62.5, etc…., X=100.