Results

Figure  shows sections of 9 independent components (IC's) found from the recorded data, corresponding to a 1 min period, starting 1 min after the beginning of the measurements. The first two IC's, with a broad band spectrum, are clearly due to the musclular activity originated from the biting. Their separation into two components seems to correspond, on the basis of the field patterns, to two different sets of muscles that were activated during the process. IC3 and IC5 are, respectively showing the horizontal eye movements and the eye blinks, respectively. IC4 represents cardiac artifact that is very clearly extracted. In agreement with jousmaki, the magnetic field pattern of IC4 shows some predominance on the left.

The breathing artifact was visible in several independent components, e.g. IC6 and IC7. It is possible that, in each breathing the relative position and orientation of the metallic piece with respect to the magnetometer has changed. Therefore, the breathing artifact would be associated with more than one column of the mixing matrix A, or to a time varying mixing vector.

  

Figure: Nine independent components found from the MEG data. For each component the left, back and right views of the field patterns generated by these components are shown -- full line stands for magnetic flux coming out from the head, and dotted line the flux inwards.

To make the analysis less sensible to the breathing artifact, and to find the remaining artifacts, the data were high-pass filtered, with cutoff frequency at 1 Hz. Next, the independent component IC8 was found. It shows clearly the artifact originated at the digital watch, located to the right side of the magnetometer.

The last independent component shown, relating to the first minute of the measurement, shows an independent component that is related to a sensor presenting higher RMS (root mean squared) noise than the others.