Modulate Perceptual Learning: Transcranial Direct Current Stimulation (tDCS) reduces the Inversion Effect for faces and checkerboards

Abstract

We report here the results from a large tDCS study (n=120) investigating the effects of anodal stimulation on perceptual learning indexed by the inversion effect for face (Experiment 1a) and checkerboard (Experiment 1b) stimuli. We aimed to characterise the effects of anodal tDCS delivered at Fp3 scalp area, with the return electrode placed at Fp2 (Fp3-Fp2), vs. anodal tDCS also at Fp3, but with the return electrode placed at Cz (Fp3-Cz), and a sham/control group. The study was conducted using a double-blind procedure, where participants were randomly assigned to one of the three groups (Fp3-Fp2, Fp3-Cz, sham) and engaged with two matching task experiments, one testing the face inversion effect (Experiment 1a) and one testing the checkerboard inversion effect (Experiment 1b), presented in a counterbalanced order. The results from the anodal Fp3-Fp2 group revealed a reduced inversion effect for face and checkerboard stimuli compared to that found in the Fp3- Cz and sham groups. No differences were found between the anodal Fp3-Cz and sham groups. Our results contribute to an emerging line of research showing how a specific tDCS procedure (Fp3-Fp2) can modulate perceptual learning indexed by the inversion effect.