7.4: The Fundamental Goal of EEG Preprocessing

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This chapter and the following two chapters describe EEG preprocessing steps that are used to deal with problem in the data, such as bad channels and artifacts. First, we need to think about what our goal is for these steps. I find that most people haven’t thought clearly about what they are trying to achieve in their preprocessing pipeline, and this leads to pipelines that are less than ideal.

So, what is the goal of EEG preprocessing? It’s simple: our fundamental goal is to accurately answer the scientific question that the experiment was designed to address. If we include bad channels or large artifacts, this will likely move us away from this goal. However, if throw out a lot of trials or participants, this will also tend to move us away from our goal by reducing our statistical power. Most preprocessing steps—such as interpolating bad channels or rejecting trials with artifacts—have both costs and benefits, and we need to ask whether the benefits of a given processing step outweigh the costs in terms of answering the scientific question that the experiment was designed to address. We will discuss how to assess these costs and benefits as we go through this chapter and the next two chapters.