A common interpretation of the results of thermally stimulated current experiments is in terms of a fixed set of states present in the system with a range of activation energies, of which specific subsets are selected and identified by thermal slicing (TS) (or fractional polarization) experiments at different polarization temperatures Tp. On the other hand, such an interpretation is not consistent with many current theories of supercooled liquids and of the glass transition. The results are presented of our calculations on thermally activated Fredrickson-Andersen model systems, which indicate that the TS technique does identify the isothermal response of the system at Tp. However, this response need not be associated with specific states present in the system, but can arise for instance from a competition between different relaxation paths for the dipole moments of the individual particles. In addition, the compensation law is found to be obeyed for systems with and without cooperative effects, so that it seems to have no fundamental significance.