  Preferred frame effects (PFEs) are predicted by a number of alternative
gravity theories which include vector or additional tensor fields, besides the
canonical metric tensor. In the framework of parametrized post-Newtonian (PPN)
formalism, we investigate PFEs in the orbital dynamics of binary pulsars,
characterized by the two strong-field PPN parameters, \alpha_1 and \alpha_2. In
the limit of a small orbital eccentricity, \alpha_1 and \alpha_2 contributions
decouple. By utilizing recent radio timing results and optical observations of
PSRs J1012+5307 and J1738+0333, we obtained the best limits of \alpha_1 and
\alpha_2 in the strong-field regime. The constraint on \alpha_1 also surpasses
its counterpart in the weak-field regime.
