Frequency decomposition and phase synchronization of the visual evoked potential using the empirical mode decomposition

Abstract

ObjectivesThe phase characteristics of the representative frequency components of the Electroencephalogram (EEG) can be a means of understanding the brain functions of human senses and perception. In this paper, we found out that visual evoked potential (VEP) is composed of the dominant multi-band component signals of the EEG through the experiment.MethodsWe analyzed the characteristics of VEP based on the theory that brain evoked potentials can be decomposed into phase synchronized signals. In order to decompose the EEG signal into across each frequency component signals, we extracted the signals in the time-frequency domain with high resolution using the empirical mode decomposition method. We applied the Hilbert transform (HT) to extract the signal and synthesized it into a frequency band signal representing VEP components. VEP could be decomposed into phase synchronized δ, θ, α, and β frequency signals. We investigated the features of visual brain function by analyzing the amplitude and latency of the decomposed signals in phase synchronized with the VEP and the phase-locking value (PLV) between brain regions.ResultsIn response to visual stimulation, PLV values were higher in the posterior lobe region than in the anterior lobe. In the occipital region, the PLV value of theta band was observed high.ConclusionsThe VEP signals decomposed into constituent frequency components through phase analysis can be used as a method of analyzing the relationship between activated signals and brain function related to visual stimuli.

Intact memory storage but impaired retrieval in visual memory in autism: New insights from an electrophysiological study

“…As alpha and beta desynchronization has been associated with the reactivation of long‐term stored information (Hanslmayr et al, 2012), including semantic memories (Klimesch, 1996; Klimesch et al, 1997) and high‐fidelity representation of episodic memories (Griffiths et al, 2019; Karlsson et al, 2020), this result might suggest a relative preservation of stored information in ASD. By contrast, the conjunction of early reduced theta and delta ERS (150–300 ms), in occipito‐parietal ROIs, may underlie a decrease in visual attention and priming (Freunberger et al, 2007; Karakaş, 2020; Lee et al, 2020). In later time‐windows, reduced theta ERS suggests weaknesses in electrophysiological processes supporting access to and manipulation of both semantic and episodic information (Düzel et al, 2003; Hsieh & Ranganath, 2014; Klimesch et al, 2010; Mitchell et al, 2008; Wynn et al, 2019).…”