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Human achromatic flickers and phosphenes thresholds under extremely low frequency electric stimulations
Nicolas Bouisset1,2, Andres Carvallo3, Maorie Laporte3
1Human Threshold Research Group, Lawson Research Institute, London, ON, Canada. nbouisset@lawsonimaging.ca.
Scientific Reports
|July 3, 2025
Summary
Extremely low-frequency electric fields can cause visual phosphenes. This study found phosphene perception thresholds varied by frequency, being lowest at 20 Hz and undetectable at 100 Hz, informing safety guidelines.
Area of Science:
- Biophysics
- Neuroscience
- Electromagnetic Field Exposure
Background:
- Extremely low-frequency (ELF) electric and magnetic fields (EMFs) induce visual phosphenes, a stroboscopic perception.
- Phosphene induction is a primary basis for international guidelines limiting human exposure to ELF EMFs.
Purpose of the Study:
- To estimate the phosphene perception locus and threshold at various frequencies (20, 50, 60, 100 Hz) during electric current stimulation.
- To estimate the associated in-situ electric field in the retina.
Main Methods:
- Non-invasive transcranial alternating current stimulation (0-2 mA) was applied to 20 volunteers at 20, 50, 60, and 100 Hz.
- Binary logistic regressions analyzed perceptual responses to determine phosphene perception probabilities.
- Dosimetry analysis quantified the in-situ electric field induced in the retina.
Main Results:
- Stimulation current significantly influenced phosphene perception predictions across all tested frequencies.
- Phosphene perception thresholds were lowest at 20 Hz.
- No perceptible phosphenes were observed at 100 Hz.
Conclusions:
- Findings support the retinal origin of phosphenes.
- The study provides crucial data for understanding phosphene induction mechanisms.
- Observed thresholds and trends will inform updates to international EMF exposure guidelines and standards.
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