Sofía, only 18 months of age, is learning to use the toilet. First, her parents give her smiles and hugs when Sofia walks into the bathroom. Then they give her songs and praise when she points to the potty. When she agrees to sit on the potty seat, her parents sing and dance, making her smile and laugh. Finally, when she begins to actually use the potty, her parents give her some candy that she loves. Sofía is being taught to use the potty through which of the following processes?