Performance by Exclusion and Expansion of Functional Classes

Functional classes, formed by the partition of a set of stimuli, can be expanded by the direct training of new stimuli. Unknown, however, is whether new stimuli can be added to classes through indirect training procedures. The present study investigated whether functional classes can be expanded with the inclusion of new stimuli from exclusion procedures. In Study 1, 20 undergraduate students and 20 children learned three simple visual simultaneous discriminations. After successive reversals of the stimulus functions, an exclusion test was conducted with two new stimuli, followed by three class expansion tests, with the presentation of the pair of new stimuli and reversals of the stimulus functions. One third of the two groups exhibited performance by exclusion. Most of the students attributed the new stimuli to the classes in a way that was unrelated to their performance in the exclusion test. The children responded irregularly to the new stimuli in the class expansion tests. In Study 2, an exclusion test was added to the procedure, prior to the successive reversals. The participants, seven undergraduate students, responded by exclusion in the first test, but only three did so in the second test. Participants who responded by exclusion in the second test exhibited expansion of the classes, including the new stimuli into the classes. Successive reversal procedures interfere with the stability of the function of the stimuli in the class, which hinders the performance of participants in exclusion probes. We discuss the implications of studying the expansion of functional classes.