  The first quantum correction to the IIA string effective action arises at the
eight-derivative level and takes the schematic form (t_8 t_8 - 1/8
\epsilon\epsilon)R^4 + B_2 \wedge X_8. This correction, however, cannot be
complete by itself, as it is neither supersymmetric nor T-duality covariant. We
reexamine these eight-derivative couplings and conjecture that the simple
replacement R -> R(\Omega_+), where \Omega_+ = \Omega + 1/2 H is the connection
with torsion, nearly completely captures their dependence on the B-field. The
exception is in the odd-odd spin structure sector, where additional terms are
needed. We present here a complete result at the level of the five-point
function and a partial one for the six-point function. Further evidence for
this conjecture comes from considering T-duality as well as heterotic/IIA
duality beyond leading order. Finally, we discuss the eleven-dimensional lift
of the modified one-loop type IIA couplings.
