On the generality of choice ordering in object retrieval by Norway rats

These studies examined choices made in the course of object retrieval when more than one kind of object was available. During a retrieval session, or `trial', a rat could (repeatedly) retrieve either of two types of object drawn from a set of three, when each type of object was located in one arm of a Y-maze connected to the home cage. In Experiment 1 objects varied in degree of partibility, i.e. their capacity to be taken apart by gnawing. Experiment 2 included sweet and partible objects. In both studies, after a series of trials, each rat developed a stable preference hierarchy, in terms of relative numbers of objects retrieved, that depended on choices distributed through most of the retrieval sequence. As in studies with sweet objects, responsiveness to the middle object in a hierarchy was higher when it was paired with the less- than with the more-preferred object. After preferences stabilized, each trial began with a period of sampling, followed by rapid shifts in responsiveness in favor of the preferred object. This work shows that the capacity to order choices and retrieval preferences holds for different object features and across motivational boundaries.