Fig. 1

Visual oddball paradigm. The paradigm included the frequent neutral (NT; 75 %), and infrequent angry (ANG; 6.25 %) and happy (HAP; 6.25 %) gray-scaled faces, which were represented by self-making illustrations, and white circle targets (12.5 %). These stimuli were pseudo-randomly presented in the center of random-dot backgrounds so that the ANG and HAP faces or targets did not appear successively in each of the three blocks (160 stimuli for each block). Participants were instructed to press a button with their right index finger as rapidly as possible, when targets appeared. All stimuli were presented for 200 ms with the stimulus-onset-asynchrony (SOA) fixed at 500 ms. Response times for targets appearing immediately after the ANG and HAP faces were averaged to examine interference effects on button responses. Averaged event-related potential (ERP) waveforms were produced separately for the NT, ANG, and HAP faces