I think it doesn't make sense to average several channels. If you wanted to have just one channel, then why did you use a 32 channel montage?

Dear Lydia Girard-Tremblay,

There are multiple ways to average the multiple channels reading into single one. Simplest of them being averaging across channels by keeping the time axis as it is. Averaging increases the SNR of the recorded signals making them discernible and allowing for better interpretation. This has a simple mathematical explanation provided that some simplifying assumptions are made. These assumptions are:

So be aware of consequences as well.

Dear Lydia,

If I understand correctly, the "averaging" you want to perform is not supposed to be a pre-processing step, but a step in visualisation, or in other words: you have 11 channels that constitute your ROI and you want to plot the averaged wavelengths (although 11 channels out of 32 seems quite a large ROI). If that is correct, then the solution in BVA is simple: after all the pre-processing and grand-averaging, simply create a new channel with Formula Evaluator. In more details, go to your secondary files, select the final node you want to visualise, go to Transformations --> Formula Evaluator and create a new channel made up with the average of your ROI channels (e.g. "ROI = (ch1 + ch2 + ch3)/3"). Then you can simply select this new channel in the newly created node and adjust the plot as always.

Hope that helps!