dc.description.abstract | In this thesis, we applied the Holo-Hilbert spectral analysis (HHSA) method to analyze heart rhythm variability (HRV) in ECG. Human Auditory steady-state response analysis (ASSR) Canonical Correlation Analysis (CCA) combined with Holo-Hilbert spectral analysis (HHSA) was also performed using canonical correlation analysis. CCA is used to extract ASSR-related signal features, and the extracted ASSR response is decomposed into amplitude modulation (AM) components and frequency modulation (FM) components using Holo-Hilbert spectral analysis (HHSA), where FM frequency represents a rapidly changing intra-mode frequency, AM frequencies represent slowly varying intermodal frequencies. In the analysis of heart rhythm variability (HRV), Holo-Hilbert spectral analysis (HHSA) intends to interpret the measured heartbeat interval (IBI) signal as a combination of a multiplicative oscillatory signal (carrier wave) and a modulating signal (envelope wave). Instantaneous frequency analysis (IFA) was used to calculate the frequency of frequency modulation (FM) and amplitude modulation (AM) at each time point. The FM-AM distribution probabilities of the entire measured IBI signal are accumulated and displayed on the Holographic-Hilbert Spectrum (HHS).
Twenty healthy subjects were recruited for our ECG study. Each subject was asked to watch two video clips, including a relaxing video clip and a horror video clip. We observed that the VHF band was modulated by ~0.05 Hz AM frequency on Holo-Hilbert spectral analysis(HHSA). VHF power values were significantly lower when watching a horror video clip compared to watching a relaxing video clip. We also found reduced power on both the VHF and high frequency (HF) bands when watching horror video clips.
In the ASSR analysis, we aimed to study the ASSR responses to 37 Hz, steady-state auditory stimuli in the AM and FM spectra.
Twenty-five healthy subjects were recruited to participate in this study, and each subject was asked to participate in two auditory stimulation experiments, including one right ear and one left ear, and a steady-state auditory stimulus for one ear. Hearing responses at 37 Hz (fundamental frequency) and 74 Hz (first harmonic frequency) were successfully extracted in the Holo-Hilbert spectral Analysis (HHSA) graph. Examining the AM spectrum, the 37 Hz and 74 Hz auditory responses are modulated by different AM spectra, each with at least three composite frequencies. Contrary to the results of conventional Fourier spectroscopy, frequency division occurs at 37 Hz, and in Fourier spectroscopy, the spectral peak is blocked at 74 Hz. The proposed method effectively corrects the frequency division problem caused by time-varying amplitude changes.
Finally, Holo-Hilbert spectral Analysis (HHSA) provides a new perspective to analyze HRV and Steady State Response (SSR), and thus is a useful analytical interpretation tool, in Steady State Response (SSR), avoidance can be reduced, since False, or misleading interpretations caused by amplitude modulation in conventional Fourier spectrum.
Keywords: Heart rhythm variability、Auditory steady-state response、Canonical correlation analysis, Holo-Hilbert spectral Analysis
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