  We investigate quantitatively the effects of strong electron-electron
coupling onto the dynamics of lattice electrons. To that purpose the
self-consistent version of the bubble-chain approximation at zero temperature
and half filling of the Anderson (Hubbard) model is used. Special attention is
paid to a critical region of an electron-hole correlation function shaping the
transition from weak to strong interaction. We find an analytic solution with
Fermi-liquid properties on the weak-coupling side of the critical region around
the two-particle pole. It is shown that Fermi-liquid theory does not lead to a
consistent behavior of the self-consistent solution on the strong-coupling side
of the critical region.
