Improving the homogeneity of the magnetic field in the magnetic search coil technique.

The magnetic search coil technique is used to obtain accurate eye-movement measurements. For the data analysis it must be assumed that the magnetic field does not change over time (apart from the required modulation). To comply with this assumption either no translational movements of the eye coil(s) are allowed or the magnetic field has to be perfectly homogeneous. Both are normally not the case, i.e., measurement errors occur. These errors can be minimized by keeping the magnetic field as homogeneous as possible. Larger field coils are typically chosen to achieve this aim. However, sometimes the experimental setup imposes limitations on the size of the configuration. We present a method for improving the homogeneity of the magnetic field by adding supplementary field coils without changing the size of the configuration.