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The effect of the stimulus eccentricity on the main component of the steady‐state visual evoked potential
Author(s) -
Solf Benjamin,
Blum MarenChristina,
Klee Sascha
Publication year - 2021
Publication title -
acta ophthalmologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.534
H-Index - 87
eISSN - 1755-3768
pISSN - 1755-375X
DOI - 10.1111/j.1755-3768.2020.0181
Subject(s) - luminance , evoked potential , foveal , stimulus (psychology) , amplitude , visual evoked potentials , eccentricity (behavior) , magnification , physics , electrophysiology , steady state (chemistry) , harmonic , mathematics , optics , audiology , nuclear magnetic resonance , chemistry , medicine , neuroscience , ophthalmology , acoustics , psychology , retinal , social psychology , psychotherapist
Purpose For electrophysiological functional diagnostics, the main component of steady‐state visual evoked potentials (SSVEP) at stimulation frequency (SF) is mainly used. However, some studies reported the main component at the second harmonic of the SF. A possible cause are signal components of the single responses that differ from the SF when the responses overlap during steady‐state stimulations, but the origin is not fully understood. The aim of our study was to investigate the effect of the stimulus eccentricity on the occurrence of the main component of SSVEP. Methods We studied 14 healthy subjects (5 m, 28 ± 5.0 years) using a circular layout (r 1 = 0–1.6°, r 2 = 1.6–3.5°, r 3 = 3.5–6.4°, r 4 = 6.4–10.9°, r 5 = 10.9–18°). The dimensions of the stimuli were scaled according to the cortical magnification. The stimuli (luminance: 350 cd/m 2 , contrast: 99%) were presented in a random order at 7.5Hz for 75 cycles for each eccentricity. This procedure was repeated 10 times in total (750 cycles per eccentricity). A background luminance of 30 cd/m 2 was added to supress foveal stray light effects. The electrodes were placed at Oz (active), FCz (reference) and FPz (ground). The recorded SSVEP were transformed using Fourier analysis. The medians (M) of the normalized amplitude ratios for amplitudes at first and second harmonic were calculated. Friedman's test ( α = 0.05) and the probability of the occurrence of the main component at the second harmonic (P(MCSH)) were used for statistical analysis. Results The normalized amplitude ratios showed a significant difference for the 5 stimulus eccentricities (M r1 = 0.45, M r2 = 0.41, M r3 = 0.72, M r4 = 0.72 M r5 = 0.67; p = 0.0002*). P(MCSH) showed an increase for stimulus eccentricities for ≥r 3 (P(MCSH) r1 = 0.07, P(MCSH) r2 = 0.07, P(MCSH) r3 = 0.36, P(MCSH) r4 = 0.29, P(MCSH) r5 = 0.36). Conclusions The stimulus eccentricity has an influence on the main component of SSVEP. An increase in stimulus eccentricity leads to an increased occurrence of the main component at second harmonic.