An ongoing debate in III-V compound semiconductors has focused on whether state mixing occurs between the light-hole and heavy-hole valence bands. This question has led to the proposal of two distinct sets of interband optical transition selection rules: one assuming the presence of state mixing and the other assuming its absence. In this letter, we aim to experimentally determine the validity of these two selection rules by performing wavelength-dependent circular dichromatic differential transmission dynamic measurements on intrinsic and n-doped GaAs films. Ultimately, we demonstrate that both sets of selection rules may be valid but apply to different regions of k-space within the Γ valley. A quantitative criterion is given out. Further, spin relaxation time of holes in split-off valence band is obtained for the first time as ~30.6 femtoseconds.