Comparison of Different Methods of Time Shift
Measurement in EEG

P. JIRUŠKA^1,2,3, J. PROKŠ⁴, O. DRBAL⁴, P. SOVKA⁴, P. MARUSIČ⁵, P. MAREŠ<sup>1

1</sup>Institute of Physiology, Academy of Sciences of the Czech Republic, Departments of ²Physiology, ³Pediatric Neurology, and ⁵Neurology, Charles University, Second Faculty of Medicine and ⁴Department of Circuit Theory, Czech Technical University, Faculty of Electrical Engineering, Prague, Czech Republic

Received October 7, 2004
Accepted October 13, 2004
On-line available December 9, 2004

Summary
Digital signal processing techniques are often used for measurement of small time shifts between EEG signals. In our work we tested properties of linear cross-correlation and phase/coherence method. The last mentioned method was used in two versions. The first version used fast Fourier transform (FFT) algorithm and the second was based on autoregressive modeling with fixed or adaptive model order. Methods were compared on several testing signals mimicking real EEG signals. The accuracy index for each method was computed. Results showed that for long signal segments all methods bring comparably good results. Accuracy of FFT phase/coherence method significantly decreased when very short segments were used and also decreased with an increasing level of the additive noise. The best results were obtained with autoregressive version of phase/coherence. This method is more reliable and may be used with high accuracy even in very short signals segments and it is also resistant to additive noise.

Key words
EEG • Time shift • Signal processing • Cross-correlation • Phase/coherence