Spatial Vector-based Approach to the ERP Analysis as Applied to an EEG-based Discrimination of Traffic Light Signals

Abstract

The purpose of the study was to assess the utility of the spatial vector-based representation of multichannel electroencephalography (EEG; when each spatial vector denotes an "instantaneous" sample of cortical activation evolving over time) in the analysis of cortical responses to visual stimulation-as opposed to the traditional, temporal vector-based approach, when vectors are associated with distinct EEG channels. This representation was used in the analysis of EEG collected in the virtual traffic light environment with the attempt to determine the color of traffic light perceived by four participants. Kruskal-Wallis (K-W) analysis of variance was implemented for selected EEG electrodes. To utilize all available information, discrimination value was evaluated next for 32dimensional EEG spatial vectors followed by modified "k nearest neighbors" (knn) classification. K-W test indicated that EEG samples at selected electrodes are different between different colors of traffic light and when observed for specific latencies. The average accuracy of a modified three-class knn classifier was approaching 60% (the random assignment would yield approximately 33%) for the specific poststimuli latencies. The proposed technique allows analyzing stimulation-synchronized cortical activity with the temporal resolution generally determined by the sampling rate of the neuroimaging modality. The discrimination value appears instrumental for predicting the clusterability of data assessed. Stimulation-evoked cortical responses are often of interest in studies of human cognition. The proposed technique may overcome the low signal-to-noise limitation of the traditional evoked response potential (ERP) analysis and possibly provide means to assess such responses under the real-time constraint.

An “Instantaneous” Response of a Human Visual System to Hue: An EEG-Based Study

“…We have previously illustrated that an EEG epoch can be alternatively viewed as a sequence of “instantaneous” spatial vectors that evolve over time. This approach was shown to be instrumental for the VEP analysis [ 16 ] and appears suitable for studying the timing of stimulation-locked cortical activities with higher accuracy. Therefore, we will adopt the underlying concepts for the present study.…”

“…The temporal vector concept can be used to estimate the VEPs. We suggest that the spatial vector representation “may be more adequate for the analysis of the perception-related alterations in the temporal distribution of the cortical activity” [ 16 ]. We also maintain that a spatial EEG vector can be viewed as an “instantaneous” snapshot of cortical activity taken from all available (or pre-selected) EEG channels.…”