ABSTRACT
Three classification designs are considered. In a same-different experiment, a pair of stimuli is presented on each trial, and the observer decides whether they are the same or different. The independent-observation strategy makes covert classifications about the two observations independently, whereas in the difference strategy only the difference between the two observations is used in making a decision. In an ABX experiment, three stimuli are presented on each trial; the third presentation matches one of the first two, and the observer’s task is to decide which. The independent-observation strategy is to assess independently (a) the difference between A and B, and (b) X, whereas for the difference strategy, two differences contribute to the decision: A − X and B − X. In a three-alternative oddity experiment (triangle task), two of the three presentations are the same. The observer must select the “odd” one out. The independent-observation strategy requires covert identification of all presentations, whereas in the difference strategy, the smallest of the three differences is determined and the response corresponds to the stimulus that does not contribute to it.
