Effect of response-contingent vs. noncontingent shock on ducklings’ preference for novel imprinting stimuli

Individual ducklings received electrical shock in the presence of an imprinting stimulus whenever they pecked at food. Other ducklings received an identical series of shocks in the presence of an imprinting stimulus, but for them shock delivery was independent of their pecking behavior. In a subsequent session, the use of shock was discontinued and all birds were afforded the opportunity to approach either the imprinting stimulus (i.e., the stimulus previously present during shock) or a novel imprinting stimulus that was simultaneously presented. Ducklings that were shocked when they pecked at food either exhibited no preference or they preferred the original imprinting stimulus. In contrast, birds for whom shock was independent of their feeding behavior preferred the novel stimulus. These findings imply that the delivery of shock in the presence of an imprinting stimulus can endow the stimulus with conditioned aversive properties. They also imply that the stimulus will acquire little or no aversiveness if shock delivery is contingent upon a specific response such as pecking.