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Data Acquisition and Preprocessing 

Data Acquisition and Preprocessing
Chapter:
Data Acquisition and Preprocessing
Author(s):

Riitta Hari

, and Aina Puce

DOI:
10.1093/med/9780190497774.003.0007
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date: 26 February 2021

This chapter introduces principles of MEG/EEG data acquisition and preprocessing. MEG and EEG are recorded as analog (continuous-value) signals, amplified, and then filtered to remove undesirable components with lower and higher frequencies relative to the signals of interest. The analog signals are transformed to digital form by sampling (also called digitization) at rates that avoid aliasing, a very serious signal distortion described in this chapter; the appropriate sampling frequencies are at least 2 times the highest frequency in the sampled data (so-called Nyquist criterion). Different filter types (lowpass, highpass, bandpass, and notch) and their cut-off frequencies and roll-offs are examined. Examples of pitfalls that can occur with incorrectly selected filters and sampling rates are presented.

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