Ensemble Empirical Mode Decomposition Analysis of EEG Data Collected during a Contour Integration Task

Abstract

We discuss a data-driven analysis of EEG data recorded during a combined EEG/fMRI study of visual processing during a contour integration task. The analysis is based on an ensemble empirical mode decomposition (EEMD) and discusses characteristic features of event related modes (ERMs) resulting from the decomposition. We identify clear differences in certain ERMs in response to contour vs noncontour Gabor stimuli mainly for response amplitudes peaking around 100 [ms] (called P100) and 200 [ms] (called N200) after stimulus onset, respectively. We observe early P100 and N200 responses at electrodes located in the occipital area of the brain, while late P100 and N200 responses appear at electrodes located in frontal brain areas. Signals at electrodes in central brain areas show bimodal early/late response signatures in certain ERMs. Head topographies clearly localize statistically significant response differences to both stimulus conditions. Our findings provide an independent proof of recent models which suggest that contour integration depends on distributed network activity within the brain.

Combined EMD-sLORETA Analysis of EEG Data Collected during a Contour Integration Task

“…Many different source configurations can generate the same distribution of potentials and magnetic fields on the scalp [10, 11]. Thus, the analysis of such EEG data is quite involved, encompassing machine learning and signal processing techniques like feature extraction [4, 12] and inverse modeling [13]. For timely accounts of recent advancements and actual challenges in dynamic functional neuroimaging techniques, including electrophysiological source imaging, multimodal neuroimaging integrating fMRI with EEG/MEG, and functional connectivity imaging see the reviews of Bin He [14] and Jatoi et al [15].…”

“…EMD thus adaptively and locally decomposes any non-stationary signal into a sum of intrinsic mode functions (IMFs) which represent zero-mean, amplitude- and (spatial-) frequency-modulated components, henceforth called modes. IMFs are referred to as event-related modes (ERMs) in case of a decomposition of event-related potentials (ERPs), i. e. averages over many trials, of EEG data [4]. In a recent comparative study we analyzed combined EEG/fMRI data sets with with a combination of EEMD and ICA techniques.…”

“…The experimental paradigm used in our previous study [3, 4] was a contour integration task, applied to a group of 19 probands and 300 trials each. A large set of Gabor stimuli was presented repeatedly which occasionally contained a contour made up by a subset of collinearly oriented Gabor patches.…”

“…In our recent study [4], brain electrodes have been distinguished according to the timing of their stimulus response. Early responses were recorded at electrodes localized in the occipital and parietal areas of the brain, while late responses were located in frontal and medio-temporal areas of the brain.…”

“…These components represent the first and second prominent ERP peaks with latencies of roughly 100 [ ms ] and N 200 [ ms ] after stimulus onset. It has been shown in [4] that the event-related modes ERM5 most closely reflected the dominant oscillation of the grand average EEGs of the various subjects.…”