Among the wide range of potential practical applications of stimulated Raman scattering (SRS), the generation of high-power coherent radiation at frequencies inaccessible to conventional lasers remains topical. With the emergence of new and the expansion of existing applications for ultrashort light pulses the efficient conversion of such pulses via SRS has become a significant area of interest. In our study on the SRS of subpicosecond laser pulses in a barium tungstate crystal, we experimentally observed and subsequently interpreted two phenomena previously considered impossible in solid-state media: (a) constructive interference between SRS and self-phase modulation (SPM) effects, and (b) an orientational Kerr nonlinearity with a subpicosecond relaxation time. It is shown that, due to this nonlinearity, the spectral broadening of the pump pulse, arising from SPM, provides a strong Stokes seed for SRS process at the peak of the pump pulse. This results in an anomalously high SRS conversion efficiency for ultrashort pulses (20% for the fundamental vibrational mode and 35% for the secondary vibrational mode) within a simple, single-pass SRS interaction configuration. Since the orientational nonlinear response observed in barium tungstate stems from lattice defects, which are inevitable in real crystals, similar response should be expected in other crystalline materials.