ROC curve analysis to determine effects of repetition on the criteria for same–different and A Not-A tests

Judges performed over 2000 same–different tests followed by over 2000 A Not-A tests, to distinguish between ‘threshold’ sodium chloride solutions and purified water. Fitting ROC curves to the data indicated that three out of four judges used a τ-strategy for the same–different test. The hypothesis that judges might, with experience, start to categorize the stimuli and switch to a β-strategy was generally not confirmed. On changing to the A Not-A method, half the judges appeared to continue initially to use the τ-strategy. The hypothesis that judges might make comparisons with the preceding stimulus rather than the standard stimulus, because of prior extensive experience with the same–different test, was generally not confirmed. Yet, in all cases there were exceptions.