  We present an experimental and theoretical investigation of the Generalized
Einstein Relation (GER), a particular form of a fluctuation-dissipation
relation, in an out-of-equilibrium visco-elastic fluid. Micrometer beads, used
as thermometers, are immersed in an aging colloidal glass to provide both
fluctuation and dissipation measurements. The deviations from the Generalized
Einstein Relation are derived as a function of frequency and aging time. The
observed deviations from GER are interpreted as directly related to the change
in the glass relaxation times with aging time. In our scenario, deviations are
observed in the regime where the observation time scale is of the order of a
characteristic relaxation time of the glass.

Soft Condensed Matter