  To elucidate the role in hadron structure of quark zero modes associated with
instantons, the lowest eigenfunctions of the Dirac operator have been
calculated in quenched QCD, full QCD, and full QCD with cooling. Eigenmodes
associated with a single instanton and an instanton-anti-instanton pair were
studied to understand the role of lattice artifacts for Wilson Fermions. By
truncating the spectral representation of the quark propagator, we show that
the rho and pion contributions to the vector and pseudoscalar correlation
functions are dominated by the zero-mode contributions.
