  The observed spectral lags of gamma-ray bursts (GRBs) have been widely used
to explore possible violations of Lorentz invariance. However, these studies
were generally performed by concentrating on the rough time lag of a single
highest-energy photon and ignoring the intrinsic time lag at the source. A new
way to test nonbirefringent Lorentz-violating effects has been proposed by
analyzing the multi-photon spectral-lag behavior of a GRB that displays a
positive-to-negative transition. This method gives both a plausible description
of the intrinsic energy-dependent time lag and comparatively robust constraints
on Lorentz-violating effects. In this work, we conduct a systematic search for
Lorentz-violating photon dispersion from the spectral-lag transition features
of 32 GRBs. By fitting the spectral-lag data of these 32 GRBs, we place
constraints on a variety of isotropic and anisotropic Lorentz-violating
coefficients with mass dimension $d=6$ and $8$. While our dispersion
constraints are not competitive with existing bounds, they have the promise to
complement the full coefficient space.
