Abstract
Electroencephalography (EEG), e.g., steady-state visual evoked potentials (SSVEPs), has been used as an alternative method to estimate visual acuity objectively over 40 years. By varying the spatial frequency of the visual stimuli, visual acuity can be measured by establishing the mathematical model between spatial frequency and SSVEP signals. Previous studies have found that SSVEPs are affected by stimulus orientation, and its influence also shows the difference to visual stimuli with various spatial frequencies, while the visual acuity threshold determination criterion is based on the relationship between SSVEP amplitude and spatial frequency. However, to date, little is known about the effect of stimulus orientation on SSVEP visual acuity assessment. Here, based on the vertical orientation, the mainly used visual stimulus in SSVEP visual acuity, the sinusoidal gratings, can form four different types of vertical, 45º, horizontal, and 135º orientations by rotating clockwise per 45º. Six logarithmically equidistant spatial frequency steps of 3.0, 4.8, 7.5, 12.0, 19.0, and 30.0 cycles per degree (cpd) corresponding to the visual acuity optotypes of 1.0, 0.8, 0.6, 0.4, 0.2, and 0.0 logMAR (log minimum angle of resolution) were presented to ten subjects for all these four visual stimuli to evoke SSVEPs. Taking the SSVEP amplitude and SNR of the fundamental reversal frequency as signal characteristics, both the SSVEP amplitude and SNR at 3.0 cpd among four stimulus orientations had no significant difference. Besides, the SSVEP visual acuity obtained by the threshold estimation criterion for all four visual stimuli also showed no significant difference. This study demonstrated that the SSVEPs induced by all these four visual stimuli had a similarly good performance in evaluating visual acuity, and the stimulus orientation had little effect on SSVEP response as well as the SSVEP visual acuity.