Object retrieval by Norway rats as a framework for preference and choice

Object retrieval by Norway rats consists of locomotion to an object, object seizure, carriage to a refuge and release. These studies examined choices in this sequence and object preferences (relative numbers retrieved) for objects varying in sweetness. In Experiment 1, rats could retrieve two types of object on each trial, drawn from a set of three, each placed in quantity in one arm of a Y-maze connected to the home cage. After a period of learning, a stable preference hierarchy was demonstrated that depended on choices in different parts of the retrieval sequence i.e. decision making was broadly distributed. For the middle object in the hierarchy, response probabilities varied with object pairing, suggesting that rats responded in terms of object-sets. Preferences also involved rapid updating at the beginning of each trial (working memory) manifested in shifts in responding in all segments that supported consistent choices. Experiments 2–3, with an empty arm as an extra alternative, indicated that visits to an arm with less-preferred objects represented exploration interspersed with retrieval. Preference and choice are fundamental to object retrieval in this species and choice consistency in a dynamic environment is based on learning and memory.