Thirteen healthy subjects (all right-handed male, age 23.2±4.6 years) with no prior history of neurological injury were enrolled. Before undergoing the examination, they gave their written informed consent to the experimental procedures, which were approved by the local Institutional Ethics Committee. The study consisted of a visual oddball paradigm, with the presentation of 80% of frequent stimuli and 20% of rare stimuli respectively. The subjects were asked to count the rare events and to report their number at the end of the session. The stimuli consisted of yellow (frequent events) and blue (rare events) disks, appearing on a black background with 200 ms duration, and presented in random order every 2.5 s (Supplementary Fig. 1). The visual images were prepared using the Cogent 2000 toolbox (www.vislab.ucl.ac.uk), running in the MATLAB (The Mathworks Inc., Natick, MA, USA) programming environment. They were generated by a NEC projector (NEC Corporation, Tokyo, Japan) working at 60 Hz refreshment rate, projected outside the scanner onto a translucent screen placed at the end of the scanner bore, and visible to the subject via a mirror attached
