1) An observer repeats the action that is performed by a model.

2) behaviour that duplicates some properties of the behaviour of a model. In-dtation need not involve the matching of stimulus features (e.g., when one child imitates the raised hand of another, the felt position of the child's own limb has different stimulus dimensions than the seen position of the other child's).

3) The behaviour of the imitator is under stimulus control of the behaviour of the model and matches the behaviour of the model.

4) Matching the behaviour of a model, or engaging in a behaviour similar to that observed.