The anisotropic EPR signal already observed in x-ray-irradiated yttria-stabilized zirconia is analyzed between 140 and 300 K in samples containing 12% and 24% ${\mathrm{Y}}_{2}$${\mathrm{O}}_{3}$. A temperature-dependent broadening is detected and attributed to spin-lattice interactions whose mechanisms are discussed. The analysis of the data as a function of the concentration of stabilizing oxide contributes to explanation of the stability properties of the center, also studied by means of isochronal and isothermal pulsed annealings. The results confirm the already proposed model and the intrinsic nature of the defect.