Conditional Discriminations by Preverbal Children in an Identity Matching-to-Sample Task.

This study sought to develop methodology for assessing whether children aged 16-21 months could learn to match stimuli on the basis of physical identity in conditional discrimination procedures of the type routinely used in stimulus equivalence research with older participants. The study was conducted in a private room at a daycare center for children and toddlers. The child and the research sat together on the floor facing an apparatus with two windows. Stimuli to be discriminated were toys especially designed to attract the child's attention and maintain continued interest. On simple discrimination and discrimination reversal trials that were programmed in initial training, S+ and S- toys were displayed within the two windows. When the child touched the window containing the toy defined as S+ on a given trial, s/he was allowed to manipulate/play with that toy. Selections of the S- toy ended the trial without a play opportunity. On subsequent identity matching-to-sample trials, the child was first allowed to manipulate a sample toy. Then, S+ (matching) and S- (nonmatching) comparison toys were displayed within the windows, and the selection consequences were the same as on simple discrimination trials. The study provides evidence that preverbal children can master simple and conditional discrimination performances via such procedures, perhaps setting the stage for subsequent studies aimed at establishing procedural control of the discrimination baselines needed to assess the stimulus equivalence potential of children in this age range.