Grand average difference waves in the psychological increment condition.
Difference waves were created by subtracting frequently occurring 80–80 dB SPL standard pairs in the oddball decrement condition (80–80…80–80…80–60…80–80) from deviant occurrences of these pairs in the psychological increment condition (80–60…80–60…80–80…80–60). The onset of the second stimulus (when deviance from the standard pattern occurs) is set at 0 ms in this figure. A large amplitude MMN was evident over fronto-central areas of the scalp between 150 and 200 ms following presentation of the psychological increment. The MMN inverted in polarity at the mastoids. However, this inversion failed to reach significance at either the M1 or M2 electrode sites. A centrally maximum non-significant P3a-like wave is evident at approximately 280 ms.