Habituation and extinction in an approach–avoidance test: An example with sheep

During a behavioural test, the test animal's perception of the test situation may change, e.g. as a result of habituation. This change can occur within a test or between repetitions of a test. It is particularly important in the arena test because in an approach–avoidance situation, the negative stimulus may not be followed by the negative consequences it is initially associated with (tested ‘in extinction’). In this experiment, we tested single sheep for 10 min in a situation of conflict between either being too close to a negative stimulus (human being) or too far away from a positive stimulus (conspecifics). The test was carried out over four consecutive days, each sheep being tested once a day. We recorded the distance between the test sheep and the conflicting stimuli, the occurrence of urination and rumination and the duration of sniffing during the test. Principal components analysis (PCA) revealed three main components of distance; the average (76%), a linear (11%) and a quadratic change across time (6%). Distances decreased within and across tests and the occurrence of urination decreased, while rumination and sniffing increased across tests. These changes of behaviour across time suggest that extinction of the conditioned response occurred within as well as across tests. These results highlight the importance of choosing the appropriate duration for a test, particularly when the test is carried out in extinction.