Performance on traditional matching to sample, non-matching to sample, and object discrimination tasks by 12- to 32-month-old children. A developmental progression.

Children 12 to 36 months old were tested on DMS, DNMS, and object discrimination tasks in a WGTA with procedures that closely followed those used previously with monkeys. Mastery of DNMS showed a clear developmental progression. The youngest children (12-15 months old) required extensive training, and they failed to reach criterion until they were 15-18 months old. The differentially slower learning of the youngest children cannot be attributed to "performance" deficits (perceptual, motivational, or associational inabilities) or the inability to make 2-part responses, because a test of object discrimination showed that even 12-month-old children can perform with accuracy in the WGTA testing situation. Analysis of learning curves along with additional tests of memory provided evidence that the youngest children are (1) less proficient in learning the novelty-reward rule and (2) less proficient in memory for a particular stimulus item. Furthermore, we found that a task that we think requires learning two rules, a DMS task, was even more difficult for children to master. These results together with data collected on brain-damaged humans and monkeys indicate that the DNMS and DMS tasks, when applied to children, may provide insight into the functional maturation of brain areas responsible for memory, rule-learning, and behavioral inhibition.