Investigating the Effect of Brain Stimulation on Motivated Reasoning

Confirmation bias, the tendency to accept information more readily when it fits existing beliefs, is well documented behaviorally but poorly understood at the neural level. Recent neuroimaging links the temporoparietal junction (TPJ) to this bias, though such work is correlational. This research proposal applies transcranial direct current stimulation (tDCS) over the TPJ to test whether altering its activity reduces confirmation bias when evaluating politically-charged claims. Each participant first completes a survey of their political views, and then judges a mixture of true and false statements that either agree or disagree with those views. Each claim is presented through a purpose-built mock short-video platform ("SlopSpace") with veracity drawn from fact-checked datasets (PolitiFact) and synthetic presenter faces (SFHQ) assigned at random so appearance is unrelated to content. Participants receive active or sham stimulation, and functional near-infrared spectroscopy (fNIRS) assesses physiological target engagement. Repeated testing measures how long any effect lasts.