  We study the influence of polarization effects in streaking by combined atto-
and femtosecond pulses. The polarization-induced terms alter the streaking
spectrum. The normal streaking spectrum, which maps to the vector potential of
the femtosecond pulse, is modified by a contribution following the field
instead. We show that polarization effects may lead to an apparent temporal
shift, that needs to be properly accounted for in the analysis. The effect may
be isolated and studied by angle-resolved photoelectron spectroscopy from
oriented polar molecules. We also show that polarization effects will lead to
an apparent temporal shift of 50 as between photoelectrons from a 2p and 1s
state in atomic hydrogen.
