Subjects need to be free of magnetic materials, like coins, watches and other metal items. Underwired bras can be a problem, and even dyes in clothing or hairdye can cause interference.
To track head movements volunteers need to have 4 small coils attached to ther head. 2 will be on the forehead and 2 behind the ears. In addition we normally also attach 5 electrodes to the face to measure eye movements and blinks.
The location of the coils needs to be measured with a 3D digitiser. We also measure 4 landmarks and a number of additional points on the head to indicate headshape and enable easier matching to an MRI structural scan.