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The Influence of the Stimulus Design on the Harmonic Components of the Steady-State Visual Evoked Potential.

ABSTRACT: 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 (r ₁ = 0-1.6°, r ₂ = 1.6-3.5°, r ₃ = 3.5-6.4°, r ₄ = 6.4-10.9°, and r ₅ = 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 M _{0 -1.6^ ?} = 0.45, M _{1.6 -3.5^ ?} = 0.45, M _{3.5 -6.4^ ?} = 0.76, M _{6.4 -10.9^ ?} = 0.72, and M _{10.9 -18^ ?} = 0.48, and the probabilities were P _{0-1.6^ ?} (MCSH) = 0.05, P _{1.6 -3.5^ ?} (MCSH) = 0.05, P _{3.5 -6.4^ ?} (MCSH) = 0.32, P _{6.4 -10.9^ ?} (MCSH) = 0.29, and P _{10.9 -18^ ?} (MCSH) = 0.30. For stimulations without foveal stray light suppression, the medians M were M _{0 -1.6^ ?} = 0.29, M _{1.6 -3.5^ ?} = 0.37, M _{3.5 -6.4^ ?} = 0.98, M _{6.4 -10.9 ^^ ?} = 1.08, and M _{10.9 -18^ ?} = 1.24, and the probabilities were P _{0-1.6^ ?} (MCSH) = 0.09, P _{1.6 -3.5^ ?} (MCSH) = 0.05, P _{3.5 -6.4^ ?} (MCSH) = 0.50, P _{6.4 -10.9^ ?} (MCSH) = 0.55, and P _{10.9 -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.

SUBMITTER: Solf B

PROVIDER: S-EPMC7509136 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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The Influence of the Stimulus Design on the Harmonic Components of the Steady-State Visual Evoked Potential.

Solf Benjamin B Schramm Stefan S Blum Maren-Christina MC Klee Sascha S

Frontiers in human neuroscience 20200909

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 (<i>r</i> <sub>1</sub> = 0- ...[more]

PMID: 33033476

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Project description:Brain-computer interface (BCI) paradigms are usually tested when environmental and biological artifacts are intentionally avoided. In this study, we deliberately introduced different perturbations in order to test the robustness of a steady state visual evoked potential (SSVEP) based BCI. Specifically we investigated to what extent a drop in performance is related to the degraded quality of EEG signals or rather due to increased cognitive load. In the online tasks, subjects focused on one of the four circles and gave feedback on the correctness of the classification under four conditions randomized across subjects: Control (no perturbation), Speaking (counting loudly and repeatedly from one to ten), Thinking (mentally counting repeatedly from one to ten), and Listening (listening to verbal counting from one to ten). Decision tree, Naïve Bayes and K-Nearest Neighbor classifiers were used to evaluate the classification performance using features generated by canonical correlation analysis. During the online condition, Speaking and Thinking decreased moderately the mean classification accuracy compared to Control condition whereas there was no significant difference between Listening and Control conditions across subjects. The performances were sensitive to the classification method and to the perturbation conditions. We have not observed significant artifacts in EEG during perturbations in the frequency range of interest except in theta band. Therefore we concluded that the drop in the performance is likely to have a cognitive origin. During the Listening condition relative alpha power in a broad area including central and temporal regions primarily over the left hemisphere correlated negatively with the performance thus most likely indicating active suppression of the distracting presentation of the playback. This is the first study that systematically evaluates the effects of natural artifacts (i.e. mental, verbal and audio perturbations) on SSVEP-based BCIs. The results can be used to improve individual classification performance taking into account effects of perturbations.

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The Influence of the Stimulus Design on the Harmonic Components of the Steady-State Visual Evoked Potential.

Publications

The Influence of the Stimulus Design on the Harmonic Components of the Steady-State Visual Evoked Potential.

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