Behavioural contrast does not occur with continuous reinforcement in the positive component

An experiment reported by Jenkins (1961) obtained positive behavioural contrast in a discrimination with continuous reinforcement of the positive stimulus. A large body of research, however, has failed to obtain positive contrast with this type of schedule. Jenkins's experiment was repeated with an added control group matched to the discrimination group in number of nonreinforced components. No positive contrast was obtained, and it was concluded that Jenkins's result could not be interpreted as positive contrast. The implications of this result for some theoretical accounts of positive contrast were discussed.