Fig. 2

a) Time domain signal of an OPM sensor during an experimental block assigned to condition 1 (loud high pitch) from the first subject. The black rectangular waveform depicts the trigger signal that marks singing (high values) and silence (low values) intervals. The blue line shows the 10 Hz high-pass filtered signal containing strong heartbeat artifacts. The Magenta line shows the same signal after removing the first PC, which leads to a strong suppression of heartbeat artifacts. The green line shows the low-pass filtered (5 Hz) envelope of the artifact free signals. For visualization purposes, the low passed envelope is mean-removed and magnified by a factor of 10. b) Low-pass filtered (5 Hz) and mean-subtracted envelopes of all channels for the same block as (a). The black waveform depicts the trigger signal. c) PCA analysis of the same block. The top left plot depicts PCA loadings of the first PC, which are mapped to the sensor positions. The time domain activity of this PC (right plots) shows that this PC mainly reflects heartbeat artifacts. The OPM positioned at the bottom left corner, which was closest to the heart, had the highest loading for the first PC. The bottom left plot shows the signal variance explained by different PCs. The first PC explained about 60% of the variance in this block.