Abstract
Components of visual cognition are consistently related to brain rhythms of different frequencies. Transcranial alternating current stimulation (tACS) offers an opportunity to directly modulate brain rhythms of specific frequencies and potentially influence behavior. However, studies using tACS to investigate the nature of visual cognition in healthy humans have yet to be systematically reviewed, and it is unclear what stimulation parameters may be most effective at changing cognitive performance. Here, we conducted a meta-analysis of all peer-reviewed, sham-controlled, tACS studies seeking to modulate human cognitive performance on visual tasks. As of November 2019, 48 publications met our inclusion criteria. Effect size (Hedge's g) and 95% confidence interval were calculated for all primary outcome measures (n = 129) to evaluate differences between active versus sham stimulation. Pooled effect sizes were calculated for each targeted cognitive domain, demonstrating a significant effect of tACS on working memory (k = 42, g = 0.280, p < 0.001), executive control (k = 21, g = 0.374, p < 0.005), attention (k = 16, g = 0.5196, p < 0.0001), learning (k = 16, g = 0.713, p < 0.0001), and general intelligence (k = 13, g = 0.497, p < 0.001). Effect sizes were calculated separately for studies that sought to impair visual cognitive performance (k = 17, g = -0.377, p = 0.05). The parameters of frequency band and stimulation location were significantly predictive of effect size magnitude. The results indicate that tACS may be an effective approach for bidirectionally steering visual cognitive performance in humans by capitalizing on the spatial and spectral properties of large-scale population activity.