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. 2014 Mar 3;8:99. doi: 10.3389/fnhum.2014.00099

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Copyright © 2014 Roberts, Paulson, Hirschkoff, Pratt, Mascarenas, Miller, Han, Caffrey, Kincade, Power, Murray, Chow, Fisk, Ku, Chudnovskaya, Dell, Golembski, Lam, Blaskey, Kuschner, Bloy, Gaetz and Edgar.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Recordings obtained in the empty MSR. (A,B) show the spectra averaged across all sensor channels. The (A) power spectrum shows several large peaks below 100 Hz. These include the 60 Hz powerline peak as well as a peak at ~24 Hz which reflects noise from the local mass transport/train system. In (B), the reference channels were used to remove external noise, the weights obtained by calculating the covariance between signal and reference channels and then the weights applied to the raw data with no temporal filtering. (B) shows that via spatial filtering most of the noise activity below 100 Hz is removed.