Transcranial alternating current stimulation (tACS) is a promising tool for modulating brain oscillations, as well as a possible/ntherapeutic intervention. However, the lack of conclusive evidence on whether tACS is able to effectively affect cortical/nactivity continues to limit its application. The present study aims to address this issue by exploiting the well-known/ninhibitory alpha rhythm in the posterior parietal cortex during visual perception and attention orientation. Four groups of/nhealthy volunteers were tested with a Gabor patch detection and discrimination task. All participants were tested at the/nbaseline and selective frequencies of tACS, including Sham, 6 Hz, 10 Hz, and 25 Hz. Stimulation at 6 Hz and 10 Hz over the/noccipito-parietal area impaired performance in the detection task compared to the baseline. The lack of a retinotopically/norganised effect and marginal frequency-specificity modulation in the detection task force us to be cautious about the/neffectiveness of tACS in modulating brain oscillations. Therefore, the present study does not provide significant evidence for/ntACS reliably inducing direct modulations of brain oscillations that can influence performance in a visual task.