Asked how she has been sleeping, a 34-year-old woman in an elated mood replies, "Sleeping, sheep, I counted sheep, sheep go to the meadow, meadow like the perfume my mother wore, my mother's coming to visit, visit, a visit to the seaside would be lovely wouldn't it," continuing in this vein for several minutes without ever returning to the original question, though each individual link is easy enough to follow. What is this?

This is flight of ideas: a rapid stream of thought with no overall direction, where each link (here, driven by rhyme and word association — sheep/meadow/visit) makes sense on its own but the sequence as a whole goes nowhere. It is not circumstantiality, in which the point is eventually reached by a slow, over-detailed but logically connected route — she never gets back to the original question at all. It is not schizophrenic formal thought disorder, because the individual links here remain, on close inspection, comprehensible, which is a key distinguishing feature. And it is more than simply talking fast, since the defining feature is the chance-driven, directionless linkage between ideas, not speed alone.