The Validity of Steady-State Visual Evoked Potentials as Attention Tags and Input Signals: A Critical Perspective of Frequency Allocation and Number of Stimuli.

Lu Wang,Zhijun Zhang,Zhenhao Zhang,Dan Han,Binbin Qian,Zhifang Liu

doi:10.3390/brainsci10090616

Abstract

Steady-state visual evoked potential (SSVEP) is a periodic response to a repetitive visual stimulus at a specific frequency. Currently, SSVEP is widely treated as an attention tag in cognitive activities and is used as an input signal for brain–computer interfaces (BCIs). However, whether SSVEP can be used as a reliable indicator has been a controversial issue. We focused on the independence of SSVEP from frequency allocation and number of stimuli. First, a cue–target paradigm was adopted to examine the interaction between SSVEPs evoked by two stimuli with different frequency allocations under different attention conditions. Second, we explored whether signal strength and the performance of SSVEP-based BCIs were affected by the number of stimuli. The results revealed that no significant interaction of SSVEP responses appeared between attended and unattended stimuli under various frequency allocations, regardless of their appearance in the fundamental or second-order harmonic. The amplitude of SSVEP suffered no significant gain or loss under different numbers of stimuli, but the performance of SSVEP-based BCIs varied along with duration of stimuli; that is, the recognition rate was not affected by the number of stimuli when the duration of stimuli was long enough, while the information transfer rate (ITR) presented the opposite trend. It can be concluded that SSVEP is a reliable tool for marking and monitoring multiple stimuli simultaneously in cognitive studies, but much caution should be taken when choosing a suitable duration and the number of stimuli, in order to achieve optimal utility of BCIs in the future.

Highlights

Steady-state visual evoked potential (SSVEP) is an elapsed period of electroencephalography (EEG) activity produced by constant-frequency visual stimulation [1,2]
The present study explored the independence of SSVEP, in terms of the frequency allocation and the number of stimuli
It was shown that the performance of SSVEP-based brain–computer interfaces (BCIs) varies with the duration of stimuli; that is, the recognition rate was not affected by the number of stimuli when the duration of stimuli was long enough, while information transfer rate (ITR) had an opposite trend

Summary

Introduction

Steady-state visual evoked potential (SSVEP) is an elapsed period of electroencephalography (EEG) activity produced by constant-frequency visual stimulation [1,2]. The study of SSVEP was first conducted for the information processing of luminance, largely for the measurement of spatial acuity and contrast sensitivity, where the paradigm was referred to as sweep visual evoked potential [3]. SSVEP has been widely adopted in feature attention [4,5], working memory [6,7], binocular competition [8,9], facial processing [10,11], biological motion [12,13], and so on. SSVEP includes fundamental frequency components to examine low-level visual processing, harmonic frequency components to characterize high-level cognitive processing, and intermodulation frequency components to measure the interaction of the nervous system [14]. SSVEP can be applied to investigate the cognitive processing mechanisms of infants or other groups with some incapacities [19,20]

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