Kammer, T., Beck, S., Erb, M., & Grodd, W. (2001). The influence of current direction on phosphene thresholds evoked by transcranial magnetic stimulation. Clinical Neurophysiology, 112, 2015-2021. Retrieved from http://www.sciencedirect.com/science?_ob=ArticleURL_udi=B6VNP-448YK7H-5_user=29041_coverDate=112F302F2001_rdoc=5_fmt=summary_orig=browse_srch=23toc2361842320012399887998823269228!_cdi=6184_sort=d_docanchor=_acct=C000003178_version=1_ur.