We recently discovered that shearing particle-reinforced rubbers in oscillation at a frequency f(a) at a small strain y(a) (e.g., similar to 1% strain) for time t(a) can often produce a spectrum hole or drop in the strain-dependent dissipation spectra of the materials. The location of the hole (or localized perturbation in the loss modulus or loss tangent) depends on the aging strain amplitude y(a). The depth of this hole is influenced by both the oscillatory aging frequency f(a) and the aging duration t(a), and follows a simple power relationship of the product of f(a) and t(a). The exponent for the power relationship is a function of filler concentration. These attributes of the spectral hole in filled rubbers are not sensitive to the frequency used to postanalyze the hole. This new memory effect occurs at very small strains and involves material stiffening during the strain aging, and both of those features are quite different from the Mullins effect in filled elastomers. We interpret this newly discovered memory character of filled rubbers from a much broader concept of structure pinning in a condensed frustrated system and consider that the agglomeration of filler particles in rubber matrix shares common physics with granular materials and glass-forming materials. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 859-869, 2010