Parity is one source of automatic reinforcement that increases the probability of verbal behavior that conforms to models provided by the verbal community. Parity as a conditioned reinforcer could explain the acquisition of grammar in the absence of direct, explicit reinforcement. This possibility has been explored in previous research on children's use of tacts with passive-voice autoclitic frames. In this study, we assessed the effects of modeling on the emission of passive-voice autoclitic frames using a pre- and post-test design with multiple training and testing phases. Thirteen children, aged 3 to 5 years, participated in the study and were randomly assigned to either a control, model-only, or model-plus-vocal-imitation group. None of the participants in the control group emitted tacts with passive-voice autoclitic frames. Eighty percent of the participants in the model-only and model-plus-vocal-imitation groups emitted passive-voice autoclitic frames, but the degree of change varied across participants. We measured whether participants attempted to echo the experimenter's passive-voice model in training, and participants in the model-only condition were much more likely to echo the model than participants in the model-plus-vocal-imitation group; nevertheless, participants in the model-plus-vocal-imitation group emitted more tacts with passive-voice autoclitic frames during testing phases. We discuss the results and mechanisms, including parity, which may account for these differences.
