International Journal of Comparative Psychology

The hypothesis that exclusion performance is a prerequisite for the stimulus equivalence class formation was assessed in preschoolers of about 5 years of age. In Experiment 1, two groups of children were trained in a set of conditional discriminations in a two-choice matching to sample format, Group 1 in an auditory-visual modality baseline, and Group 2 in a visual-visual modality baseline. Exclusion test trials included an undefined (not previously related) comparison stimulus, and a defined (i.e., related in the baseline) comparison stimulus, in the presence of an undefined sample stimulus. Selection of the undefined comparison was recorded as a correct response. Stimulus equivalence class formation was assessed by way of symmetry and transitivity test trials. Experiment 2 replicated the design of the first experiment, with the difference that exclusion was assessed independently and with a different baseline from symmetry and transitivity. Exclusion scores were higher for the auditory-visual groups than the visual-visual groups. In both modalities symmetry scores were superior to those in transitivity.  Symmetry showed independent from the exclusion performance, but transitivity was presumably dependent from it in the auditory-visual modality.