Retroactive inhibition as a function of the conceptual structure of original and interpolated lists

Subjects learned either a hierarchically structured serial list of concept instances or a list made up of the same words but without structure. These two original lists were followed by one of four interpolated lists varying in number of hierarchical levels and consisting of new instances of the concepts which occurred in the original lists. Recall of the original structured list showed heavy retroactive inhibition, with the magnitude being independent of the number of conceptual levels in the interpolated lists. For the unstructured original list, retroactive inhibition decreased as the number of conceptual levels in the interpolated list increased. Some mechanisms believed involved in producing these outcomes were discussed.