Threshold Determination Criterion in Steady-State Visual Evoked Potential-Based Acuity Assessment: A Comparison of Four Common Methods

The steady-state visual evoked potential (SSVEP) visual acuity is usually defined by extrapolating a straight line regressed through significant SSVEP amplitudes plotted versus spatial frequencies to 0 mu V or a noise level floor, or the finest spatial frequency evoking a significant SSVEP. This study aimed to compare the performance of the commonly used threshold determination criteria of the extrapolation technique and the finest spatial frequency technique. Visual acuity was measured both by the Freiburg Visual Acuity Test (FrACT) and SSVEP with vertical sinusoidal reversal gratings in ten adults. The extrapolation technique including three methods of linear extrapolation to zero (C-1), linear extrapolation to noise level baseline (C-2) and linear extrapolation to zero versus log spatial frequency (C-3), and the finest spatial frequency technique with significance determination by canonical correlation analysis (CCA) and "OR'' operation (C-4) were used to determine the SSVEP visual acuity. Bland-Altman method found a pretty good agreement between the SSVEP and FrACT acuity obtained by all the four threshold estimation criteria. One-way repeated-measures ANOVA and Bonferroni post-hoc analysis found that there was no significant difference among visual acuities measured by FrACT and all the four criteria, except for the visual acuity estimated by C-1 slightly higher than that of C-2, demonstrating that these visual acuity estimating methods had a similar performance in evaluating the visual function. The correlation and agreement between subjective FrACT acuity and objective SSVEP acuity measured by four criteria respectively were all pretty good, demonstrating that all of these four threshold estimation criteria had a good performance in SSVEP visual acuity assessment.