Abstract
Although the mechanisms of steady-state visual evoked potentials (SSVEPs) have been well studied, none of them have been implemented with strictly experimental conditions. Our objective was to create an ideal observer condition to exploit the features of SSVEPs. We present here an electroencephalographic (EEG) eye tracking experimental paradigm that provides biofeedback for gaze restriction during the visual stimulation. Specifically, we designed an EEG eye tracking synchronous data recording system for successful trial selection. Forty-six periodic flickers within a visual field of 11.5° were successively presented to evoke SSVEP responses, and online biofeedback based on an eye tracker was provided for gaze restriction. For eight participants, SSVEP responses in the visual field and topographic maps from full-brain EEG were plotted and analyzed. The experimental results indicated that the optimal visual flicking arrangement to boost SSVEPs should include the features of circular stimuli within a 4–6° spatial distance and increased stimulus area below the fixation point. These findings provide a basis for determining stimulus parameters for neural engineering studies, e.g. SSVEP-based brain-computer interface (BCI) designs. The proposed experimental paradigm could also provide a precise framework for future SSVEP-related studies.
Highlights
Steady-state visual evoked potentials (SSVEPs) are periodic visual cortical responses evoked by certain repetitive stimuli with a constant frequency and can be detected from the primary visual cortex[1,2]
Forty-six flickers covering a visual field over an angle of 11.5° were successively delivered to evoke SSVEP responses in a random sequence
The SSVEP responses were computed by the Canonical correlation analysis (CCA) algorithm using eleven channels over the occipital and parietal brain areas (P7, P3, Pz, P4, P8, PO3, POz, PO4, O1, Oz, and O2)
Summary
Steady-state visual evoked potentials (SSVEPs) are periodic visual cortical responses evoked by certain repetitive stimuli with a constant frequency and can be detected from the primary visual cortex[1,2]. Retinotopic and topographic analyses of SSVEP have rarely been used for selecting optimal stimulus properties for SSVEP-BCI design. Fuchs et al investigated competitive neuronal dynamics of early visual processing and found that SSVEP amplitude elicited by stationary stimuli decreased significantly when competing stimulus flickers were in close spatial proximity within a visual angle of approximately 4.5° or less[17]. These experimental results provide a criterion for the minimal distance between adjacent stimulus flickers in SSVEP-BCIs. Vanegas et al proposed a novel www.nature.com/scientificreports/. Recommendations for optimal SSVEP flicking arrangement to boost BCIs were discussed based on the experimental results
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