Rats smell: odour-mediated local enhancement, in a vertical movement two-action test

In two experiments, hungry rats, Rattus norvegicus, were present in one side of an operant chamber while a conspecific demonstrator in the adjacent compartment moved a single lever either up or down for a food reward. During a subsequent test session, in which these rats were allowed access to the lever for the first time, all responses were rewarded regardless of their direction. In experiment 1, rats that were prevented from observing the direction of lever movement by means of a screen showed a reliable demonstrator-consistent response bias, while rats that had observed the direction of lever movement and in addition had access to any odour cues deposited on the lever did not. In experiment 2, each rat observed another rat (the ‘viewed’ demonstrator) moving a lever either up or down. They were then transferred into the test compartment of a different operant chamber in which another rat (the ‘box’ demonstrator) had moved the lever in the same direction as the viewed demonstrator or in the opposite direction. These observer rats showed a reliable preference for their box demonstrator’s direction, but responded in the opposite direction to their viewed demonstrator. Taken together, the results of these experiments suggest that directional responding by rats in a vertical movement two-action test is influenced by demonstrator-deposited odour cues in addition to visual experience of a demonstrator’s behaviour. Furthermore, while odour-mediated local enhancement gave rise to demonstrator-consistent responding, visual observation of a conspecific appeared to have the reverse effect.