A biomagnetometer measures the magnetic field produced by the brain as a result of a visual stimulus delivered by a display device such as a cathode ray tube (CRT). The output signal of the biomagnetometer is filtered to remove noise introduced by the operation of the display device itself, such as the repetitive scan signal of the CRT, and the CRT monitor is otherwise operated from DC power to minimize periodic variations that can interfere with the detection of brain signals. The filtering is preferably accomplished using a comb-notch filter. Cancellation coils and shielding are also preferably used to remove a portion of the noise introduced by the display device. <IMAGE>
Measurement of visually induced biomagnetic responses.