The MMN depicted in Figure 12 was measured during a tone series consisting of repetitive standards that were infrequently interrupted by pitch deviants (80%:20% probability; 300 ms duration; 600 ms SOA). Standard tones (either 485, 680, 953 or 1336 Hz) were combined with deviant tones constructed to reflect easy (.67, .75) or difficult (.90, .95) discrimination ratios to create 8 120-trial blocks. Each block consisted of one standard tone and 4 deviant tones (5% each with a lower or higher frequency at each ratio), which were arranged in a pseudo-randomized sequence. During these 8 blocks (960 trials), ERPs were recorded from 8 healthy adults, who were instructed to watch silent movie clips (wildlife scenes) and ignore the tones. For the present purpose, all deviants were pooled and MMN was computed from deviant-minus-standard difference waveforms.
