Accounting for Timing Drift and Variability in Contemporary Electroencepholography (EEG) Systems

Report No. ARL-TR-5945
Authors: W. David Hairston
Date/Pages: March 2012; 30 pages
Abstract: Electroencepholography (EEG) data acquisition technology is rapidly advancing. Because it is now more feasible to use in operational environments, its use in Army-relevant applications has also increased. However, integration of EEG with other systems requires the synchronization of multiple data modalities and identification of potential sources of error. Here, we assess the degree of stimulus timing drift and encoding jitter associated with several contemporary EEG systems. The measured amount of drift and jitter is then applied to several waveforms, including simulated, real evoked potentials, and data from a "phantom" head model for the sake of assessing the functional impact of each variable. Results show a wide range of drift across systems and particularly high timing variance in one; simulations show the potential for a dramatic distortion of signals if unaccounted for within those systems with more than 0.01% drift relative to an external clock. Additional simulations show a severe impact of encoding variance. We discuss a correction algorithm, with evidence that it not only alleviates distortion caused by drift but can also improve the results yielded from signal-averaging analyses in the case of high-variance systems.
Distribution: Approved for public release
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Last Update / Reviewed: March 1, 2012