Researcher: Michael ten Caat, PhD

Other supervisor: Jos Roerdink, PhD

Thesis defense: 2008

Electroencephalography (EEG) measures electrical brain activity by electrodes attached to the scalp. Multichannel EEG refers to a measurement with a large number of electrodes. EEG has clinical as well as scientific applications, including neurology, psychology, pharmacy, linguistics, and biology. In particular for multichannel EEG, existing visualizations do not always provide the desired insight. Therefore, this thesis introduces two new multichannel EEG visualization methods.

The first method is suitable for a combination of a large number of electrodes with many time steps. This method shows a schematic overview of all electrode positions, shows measured values for specific time steps, and is provided with a context of the remaining time steps. This new method, referred to as tiled parallel coordinates, is 40% faster than an existing clinical method without loss of information.

The second method visualizes the functional relationship between brain activities in different locations using EEG coherence. Existing visualizations for multichannel EEG coherence are either hypothesis-driven or result in visual clutter. Therefore, a data-driven method was developed which reduces clutter, preserves electrode positions, and presents a clear overview. This method consists of visualizations of so-called functional units for both individual datasets and group data. This results in a summary of an extensive collection of results which otherwise would be very difficult and time-consuming to assess. Results visualize differences in EEG coherence between younger and older adults, and between people in a non-fatigued and fatigued condition.

References

• Lorist MM, Bezdan E, ten Caat M, Span MM, Roerdink JB, Maurits NM. The influence of mental fatigue and motivation on neural network dynamics; an EEG coherence study. Brain Res. 2009 May 13;1270:95-106. PMID: 19306850.
• ten Caat M, Maurits NM, Roerdink JB. Data-driven visualization and group analysis of multichannel EEG coherence with functional units. IEEE Trans Vis Comput Graph. 2008 Jul-Aug;14(4):756-71. PMID: 18467752.
• Ten Caat M, Lorist MM, Bezdan E, Roerdink JB, Maurits NM. High-density EEG coherence analysis using functional units applied to mental fatigue. J Neurosci Methods. 2008 Jun 30;171(2):271-8. PMID: 18486232.
• ten Caat M, Maurits NM, Roerdink JB. Design and evaluation of tiled parallel coordinate visualization of multichannel EEG data. IEEE Trans Vis Comput Graph. 2007 Jan-Feb;13(1):70-9. PMID: 17093337.