Blocking of Stimulus Control

Blocking is an effect that involves compound stimuli as when the first trained stimulus controls responding and not the second one (Kamin, 1969). Blocking is observed in both classical and operant conditioning, in animals as well as in humans (vom Saal & Jenkins, 1970; Williams, 1996; Dittlinger & Lerman, 2011). We carried out a study to investigate the blocking of stimulus control in rats. First, we trained chain pulling for water in the presence of either a tone or a light. Next, we reinforced chain pulling in the presence of a combination of tone and light. Very little stimulus control was evident by the stimulus that had not been established as a discriminative stimulus early during training. Procedures that produce blocking a can have practical impact in applied settings, in attempts to establish complex discrimination for example.