Evaluation of Steady-State Visual Evoked Potentials (SSVEP) Stimuli Design for Visual Field Assessment

The Brain-Computer Interface(BCI) technologies can complement with Human-Computer interaction principles enabling personalized assessment and assistance in individual’s mental well-beings. SSVEP BCI modality is not only useful in assistive and communication but also has the potential in vision assessment by leveraging unique frequency tagged responses from the visual cortex. Ocular diseases like glaucoma render necessity to detect early vision loss symptoms. SSVEP shows promising results in assessing abnormality in visual functional defects. But SSVEP characteristics and optimal performance of visual speller differ significantly from visual field assessment application scenarios. But there is no study available yet to evaluate SSVEP stimuli design optimized for visual field assessment in discriminating abnormal from normal vision conditions. So we propose three stimuli designs and evaluate them under different normal and simulated abnormal visual field scenarios. We collected both quantitative and qualitative data from twenty-one healthy subjects according to the experiment protocol. Our evaluation of the layouts considers both their usability and their visual field classification performance. We use features extracted from Canonical Correlation Analysis to evaluate the classification performance among stimuli designs and experiment parameters. Our quantitative evaluation shows the multifocal layout achieved the highest mean accuracy, 86.88±1.47%, to discriminate between normal and two abnormal visual fields. But qualitative ratings representing subjects’ preferences, mainly influenced by visual comfort, favor the concentric design over the others. Therefore, we conclude that SSVEP multifocal layout detects the changes in visual field characteristics and creates comfortable testing scenarios enabling desirable objective visual field assessment.