Structural alpha-relaxation times, tau(alpha), determined by fitting B
rillouin scattering spectra of supercooled liquids to stretched expone
ntial or Cole-Davidson phenomenological relaxation functions can produ
ce values which diverge from the results obtained by other methods as
T approaches the glass transition temperature. This apparent separatio
n of timescales has been shown to arise in CKN from the neglect of bet
a-relaxation. Guided by the mode coupling theory, a memory function wh
ich includes both alpha- and beta-relaxation was constructed empirical
ly from depolarized light scattering spectra. This memory function was
found to fit the data as well as the alpha-relaxation-only models, wi
thout requiring unphysically small tau(alpha) values. It is shown how
the neglect of beta-relaxation generally leads to underestimation of t
au(alpha), and an alternative method of incorporating beta-relaxation
in cases where the empirical model is inapplicable is described. Also,
the question of alpha-scale universality is briefly discussed.