Steady-state visual evoked potentials (ssVEPs) are commonly used for functional objective diagnostics. In general, the main response at the stimulation frequency is used. However, some studies reported the main response at the second harmonic of the stimulation frequency. The aim of our study was to analyze the influence of the stimulus design on the harmonic components of ssVEPs. We studied 22 subjects (8 males, mean age ± SD = 27 ± 4.8 years) using a circular layout (r1 = 0–1.6°, r2 = 1.6–3.5°, r3 = 3.5–6.4°, r4 = 6.4–10.9°, and r5 = 10.9–18°). At a given eccentricity, the stimulus was presented according to a 7.5 Hz square wave with 50% duty cycle. To analyze the influence of the stimulus eccentricity, a background luminance of 30 cd/m2 was added to suppress foveal stray light effects; to analyze the influence of simultaneous foveal and peripheral stimulations, stimulations are performed without stray light suppression. For statistical analysis, medians M of the amplitude ratios for amplitudes at the second harmonic to the first harmonic and the probability of the occurrence of the main response at the second harmonic P(MCSH) are calculated. For stimulations with foveal stray light suppression, the medians were M0 –1.6^ ∘ = 0.45, M1.6 –3.5^ ∘ = 0.45, M3.5 –6.4^ ∘ = 0.76, M6.4 –10.9^ ∘ = 0.72, and M10.9 –18^ ∘ = 0.48, and the probabilities were P0–1.6^ ∘(MCSH) = 0.05, P1.6 –3.5^ ∘(MCSH) = 0.05, P3.5 –6.4^ ∘(MCSH) = 0.32, P6.4 –10.9^ ∘(MCSH) = 0.29, and P10.9 –18^ ∘(MCSH) = 0.30. For stimulations without foveal stray light suppression, the medians M were M0 –1.6^ ∘ = 0.29, M1.6 –3.5^ ∘ = 0.37, M3.5 –6.4^ ∘ = 0.98, M6.4 –10.9 ^^ ∘ = 1.08, and M10.9 –18^ ∘ = 1.24, and the probabilities were P0–1.6^ ∘(MCSH) = 0.09, P1.6 –3.5^ ∘(MCSH) = 0.05, P3.5 –6.4^ ∘(MCSH) = 0.50, P6.4 –10.9^ ∘(MCSH) = 0.55, and P10.9 –18^ ∘(MCSH) = 0.55. In conclusion, the stimulus design has an influence on the harmonic components of ssVEPs. An increase in stimulation eccentricity during extrafoveal stimulation leads to a transition of the main response to the second harmonic. The effect is enhanced by a simultaneous foveal stimulation.

中文翻译：

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刺激设计对稳态视觉诱发电位谐波分量的影响

稳态视觉诱发电位 (ssVEP) 通常用于功能客观诊断。通常，使用刺激频率下的主要响应。然而，一些研究报告了刺激频率的二次谐波处的主要响应。我们研究的目的是分析刺激设计对 ssVEP 谐波分量的影响。我们使用圆形布局（r1 = 0–1.6°，r2 = 1.6–3.5°，r3 = 3.5–6.4°，r4 = 6.4–10.9°）研究了 22 名受试者（8 名男性，平均年龄 ± SD = 27 ± 4.8 岁） ，并且 r5 = 10.9–18°）。在给定的离心率下，根据占空比为 50% 的 7.5 Hz 方波呈现刺激。为分析刺激偏心率的影响，增加了30 cd/m2的背景亮度以抑制中心凹杂散光效应；为了分析同时进行中央凹和外周刺激的影响，在没有杂散光抑制的情况下进行刺激。为了进行统计分析，计算二次谐波与一次谐波幅度比的中值 M 和二次谐波出现主响应的概率 P(MCSH)。对于中心凹杂散光抑制刺激，中位数为 M0 –1.6^ ∘ = 0.45，M1.6 –3.5^ ∘ = 0.45，M3.5 –6.4^ ∘ = 0.76，M6.4 –10.9^ ∘ = 0.72，和M10.9 –18^ ∘ = 0.48，概率为 P0–1.6^ ∘(MCSH) = 0.05, P1.6 –3.5^ ∘(MCSH) = 0.05, P3.5 –6.4^ ∘(MCSH) = 0.32 , P6.4 –10.9^ ∘(MCSH) = 0.29，P10.9 –18^ ∘(MCSH) = 0.30。对于没有中央凹杂散光抑制的刺激，中位数 M 为 M0 –1.6^ ∘ = 0.29，M1.6 –3.5^ ∘ = 0.37，M3.5 –6.4^ ∘ = 0.98，M6.4 –10。9 ^^ ∘ = 1.08, M10.9 –18^ ∘ = 1.24, 概率为 P0–1.6^ ∘(MCSH) = 0.09, P1.6 –3.5^ ∘(MCSH) = 0.05, P3.5 – 6.4^ ∘(MCSH) = 0.50，P6.4 –10.9^ ∘(MCSH) = 0.55，P10.9 –18^ ∘(MCSH) = 0.55。总之，刺激设计对 ssVEP 的谐波分量有影响。中心凹外刺激期间刺激偏心率的增加导致主要响应向二次谐波的转变。同时进行中央凹刺激可增强效果。中心凹外刺激期间刺激偏心率的增加导致主要响应向二次谐波的转变。同时进行中央凹刺激可增强效果。中心凹外刺激期间刺激偏心率的增加导致主要响应向二次谐波的转变。同时进行中央凹刺激可增强效果。