Symmetric Matching to Sample in 2-Year-Old Children

The emergence of symmetric matching to sample was studied in fourteen 2-year-old children. Three two-choice, arbitrary matching-to-sample tasks were arranged successively. Each task was followed by a test of symmetric responding. The behavior required by the tasks was taught with sample stimulus-control shaping (Zygmont, Lazar, Dube, & McIlvane, 1992). Five children did not learn identity matching, which is required for sample stimulus-control shaping. Two others showed a deterioration of baseline responding when the first test was given. The participation of these seven children was stopped. The others showed symmetric responding on all tests. These results demonstrate generalized symmetric matching to sample (one aspect of stimulus equivalence) in 2-year-old children.