Abstract

A randomized, sham-controlled, double-blind trial was conducted to test the effects of transcranial direct current stimulation (tDCS) to the left prefrontal cortex (PFC). Before and after 20-min anodal stimulation, visual judgment and confidence data were collected in a global dot motion perception task. With a signal detection theoretic analysis on an experimental design of the group as a between-participant factor and the test session as a within-participant factor, we found a significant increase of metacognitive efficiency (Mratio = meta-d’/d’) in the stimulation group, but not in the sham group. Visual judgment accuracy, task difficulty, and confidence ratings did not differ either between groups or between test sessions. These results indicate that prefrontal tDCS selectively enhanced metacognitive performance while not affecting visual judgment and confidence bias. The current study provides empirical evidence for the usefulness of tDCS as a training and rehabilitation tool to enhance metacognition.