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 and interfering activities and the second only has the interference. This paper compared covariance matrix-based subtraction with conventional waveform-based subtraction, which requires that the waveforms of interference be equal at every time point between the two measurements. Our analysis showed that covariance-subtraction only requires that the time-average of the squared intensity of interference be equal between the two measurements. As a result, the method is still effective when the onset of interference differs or even their measured waveforms differ between the two measurements. The covariance- and waveform-subtraction methods were both applied to remove the interference caused by response-button-pressing finger movements in auditory-evoked MEG measurements. The results of this application demonstrated the superiority of the covariance-subtraction method over the conventional waveform-subtraction method.
Sekihara
K
K
Mind Articulation Project, Japan Science and Technology Corporation, Tokyo.
Poeppel
D
D
Marantz
A
A
Koizumi
H
H
Miyashita
Y
Y
D000465:Algorithms; D001931:Brain Mapping / Q000379:methods*; D004574:Electromagnetic Fields; D005072:Evoked Potentials, Auditory / Q000502:physiology; D005385:Fingers / Q000502:physiology; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods* / Q000592:standards; D009044:Motor Cortex / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D011597:Psychomotor Performance; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted