P3-evoking wrong notes: Unexpected, awaited, or arousing?

The effect of melodic deviance on P3 was investigated. In one condition, the opening phrases of well-known melodies were presented. Melodies ended in the midst of the phrases, either properly or with a deviant tone, as in the study of Besson and Macar (1987). In the other condition, ending phrases of melodies were presented, with the final tone either having its proper pitch or a deviant one. It was predicted that not only deviant tones of openings would evoke P3s, as in Besson and Macar's study, but also both deviant and normal tones of endings because all these tones unambigously marked the end of the present epoch. Contrary to prediction, late positive components were evoked by deviant tones only. However, it was in the endings condition only that these components displayed a parietal maximum, as P3s do. It is concluded that two factors were necessary for evoking P3s in this paradigm, one factor that was associated with deviance, the other associated with endings. It is argued that the first factor is arousal, the second factor is subjects' expectation of the closing stimulus.