By “perseveration” is intended the lag or persistence (“inertia”) of a mental process. That is, perseveration refers to process-lag as a function of the individual. It is probably best studied in terms of the effect of its presence on another immediately subsequent process. It is indirectly manifested in the realm of mental content, and the effect is usually appreciated as “interference”, “inhibition” or “carry-over”, which are symptoms of its presence.