Comparison of covariance-based and waveform-based subtraction methods in removing the interference from button-pressing finger movements

A covariance matrix-based subtraction method has recently been proposed to remove interference using two MEG measurements: The first has both target a nd interfering activities and the second only has the interference. This pa per compared covariance matrix-based subtraction with conventional waveform -based subtraction, which requires that the waveforms of interference be eq ual at every time point between the two measurements. Our analysis showed t hat covariance-subtraction only requires that the time-average of the squar ed intensity of interference be equal between the two measurements. As a re sult, the method is still effective when the onset of interference differs or even their measured waveforms differ between the two measurements. The c ovariance- and waveform-subtraction methods were both applied to remove the interference caused by response-button-pressing finger movements in audito ry-evoked MEG measurements. The results of this application demonstrated th e superiority of the covariance-subtraction method over the conventional wa veform-subtraction method.