A chiral copolysiloxane was synthesized that exhibited an N* phase in the 9-41 degreesC temperature range. A linear electro-optical response with the applied electric field was detected in the N* phase due to the electroclinic effect. At high electric fields, the linearity of the response was strongly affected by dielectric coupling. It was found, however, that the influence of dielectric coupling on the electro-optical response became zero at a particular temperature (T = 37 degreesC), which was attributed to a sign reversal of the dielectric anisotropy.