I have just started reading through the paper of Cattani–Kaplan–Schmid — Degeneration of Hodge structures (Annals of Mathematics, 123 (1986), 457–535). For the purposes here, take $f : X to S$ to be a surjective holomorphic map from a compact Kähler manifold onto a complex manifold $S$ of strictly lower dimension. In fact, just take $S$ to be a curve. Let $V_s : = f^{-1}(s)$ denote the fibre over $s in S$.

On the first page of the CKS paper, the authors write that the Hodge subspaces $$H^{p,q}(V_s)$$ do not vary holomorphically. Is there a nice way of seeing this? I would have thought that the Hodge bundle was a holomorphic vector bundle given the amount of time spent on studying *holomorphic vector bundles with integrable connections*.

I apologise in advance for my ignorance. Thank you for your time.