The Osgood surface for transfer in human associative learning is introduced (Osgood, 1949). It describes the relationship between stimulus and response similarities and transfer of learning. In this paradigm, first a list A is learned, then a list B, followed by retesting on list A. Simulation results indicate that three-layer networks with backpropagation do not only show 'catastrophic interference' but also 'hypertransfer'. Two-layer networks do not suffer from this. Hypertransfer is explained with reference to hidden-layer representations formed during learning. Since it cannot account for this very general trait of human behavior, backpropagation's role as a tool for models of human memory must be watched very carefully.