  The heterogeneous character of the Johari-Goldstein (JG) relaxation is
evidenced by molecular-dynamics simulation of a model polymer system. A
double-peaked evolution of dynamic heterogeneity (DH), with maxima located at
JG and structural relaxation time scales, is observed and mechanistically
explained. {The short-time single-particle displacement during JG relaxation
weakly correlates with the long-time one observed during structural
relaxation}.
