Nematic liquid crystals (NLCs) have been widely used in the display industry and other electrooptical fields due to their unique optical and electrical anisotropies. The continuous development of optical communication requires faster electro-optic responses of liquid crystal materials. Here, we systematically explore the electrical modification of the orientation fluctuations and the uniaxial order parameter in six negative NLCs by applying electric fields perpendicular to the average molecular orientation and using a special incidence of light. Experimental results show that the switching-on time and switching-off time of the electro-optic responses are smaller than 350 ns. The field-induced birefringence change rate of NLCs grows as the dielectric anisotropy increases. The maximum field-induced birefringence change rate is proportional to both the applied electric field and the nematic dielectric anisotropy.