Download Appendix 9 - 11 - COMET

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February 6, 2004
Mismapping Scalp EEG Channels
If scalp EEG channels are mismapped, looking at the EEG traces when subjects blink will alert
you to errors if they occur in the anterior-posterior direction (eg. F3 and P3) but errors in leftright placement (eg F3-F4) will not be detectable. The tap test will alert you to errors in this
dimension. In the example below, you should be able to see that F3 and P3 have been mismapped
because the amplitude of the blink on the F3 trace is much smaller than expected (remember, it
should be roughly the same as that seen on FZ and F4). Additionally, the amplitude of the blink
on P3 is larger than expected – remember, blink artifacts on posterior channels should be smaller
than those on more anterior channels, and in this example, the blink on P3 is larger than that on
Cz. Compare this figure to the correct mapping shown in Figure 2).
F3 and P3
mismapped. Blinks
on F3 are unusually
small, and blinks on
P3 are unusually
large.
Figure 11. F3 and P3 incorrectly mapped. Note that the amplitude of the blink is not decreasing regularly
from the front to the back of the head. The blink on F3 is unusually small, that on P3 is unusually large.
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