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A practical introduction to wavelet analysis in electroretinography
Yousif J Shwetar1, David S Lalush2, Alice Y Zhang3
1Joint Department of Biomedical Engineering, University of North Carolina and North Carolina State University, Chapel Hill, NC, USA. yousif_shwetar@med.unc.edu.
Purpose:
To provide a conceptual understanding of the continuous and discrete wavelet transforms (CWT, DWT) for clinical electroretinography (ERG) analysis, and how these methods uncover time-frequency features that complement traditional time-domain analysis.
Methods:
A technical overview without the use of mathematical formula describing the basics of CWT and DWT and implementation considerations. We also review an example of four standard ISCEV full-field ERG (ffERG) recordings from a healthy 32-year-old male.
Results:
Wavelet analysis uncovered time-frequency signatures absent in raw traces. In DA 0.01 cd s/m2 DWT scalogram, energy localized in the 2-5 Hz range, with CWT scalograms corroborating these findings. In DA 3.0 cd s/m2, a broader frequency response is seen across 10, 20 and 40 Hz center frequencies. A similar progression was found in the LA 3.0 cd s/m2, with additional low energy indices at 80 and 160 Hz. For the LA 30 Hz flicker, all frequency and time-frequency profiles effectively replicated the 30 Hz response of the cone system.
Conclusions:
CWT and DWT provide complementary and objective insight into ERG responses. Open-source MATLAB toolkit and step-by-step tutorial provided herein lower technical barriers and enable use by the broader community.
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