A Study of SSVEP Responses in Case of Overt and Covert Visual Attention with Different View Angles

Standard automated perimetry is a common visual field test in clinical practices. But the test effectiveness relies on responses from subject and technician experience in operating the test equipment. Therefore, it calls for a more objective way of measuring visual field; as such we consider SSVEP as potential suitable technique. SSVEP is extensively studied in the context of a brain-computer interface, where successful SSVEP detection relies on fovea vision. But peripheral vision is more critical in assessing the effective field of view in Glaucoma patients. So this study investigates how SSVEP responses exhibit with different view angles and subject's visual attention in peripheral vision. We designed an experiment with single flickering stimulus at three view angles horizontally. Subject performed overt, covert and no visual attention at each stimulus position, while EEG and eye tracking data are recorded simultaneously. We used spectral power amplitude ratio and maximum canonical correlation coefficients to evaluate SSVEP responses. By applying 1-way and 2-way ANOVA tests, there is no statistical significant difference among SSVEP responses when subject paid overt or covert visual attention with different view angles. This might suggest that SSVEP can be a usable approach to measure visual fields when subject oriented with covert visual attention. So reliable SSVEP responses highly depend on the choice of stimulus frequency but do not depend significantly on different visual attention and view angles.