  We measure the renormalized effective mass (m*) of interacting
two-dimensional electrons confined to an AlAs quantum well while we control
their distribution between two spin and two valley subbands. We observe a
marked contrast between the spin and valley degrees of freedom: When electrons
occupy two spin subbands, m* strongly depends on the valley occupation, but not
vice versa. Combining our m* data with the measured spin and valley
susceptibilities, we find that the renormalized effective Lande g-factor
strongly depends on valley occupation, but the renormalized conduction-band
deformation potential is nearly independent of the spin occupation.
