Laterality effects in processing tonal and atonal melodies with affective and nonaffective task instructions.

Right-handed university subjects were presented with monaural melodies that either conformed to the rules of the Western tonal system (tonal melodies) or that systematically deviated from it (atonal melodies) while containing similar contours and pitch skips. Subjects were tested under two different task instructions. One group was requested to judge whether each melody sounded correct or not (the nonaffective task); the other group had to judge whether each melody sounded pleasant or not (the affective task). The nonaffective task was found to elicit essentially no ear difference. In contrast, the affective instruction induced opposite and reliable laterality effects, depending on the valence of the response. The pleasant responses were indicative of a left hemisphere predominance and the unpleasant responses of a right hemisphere predominance. The results are consistent with the claim that the left hemisphere is biased toward positive emotions and the right to negative emotions. Moreover, the results suggest that affective appreciation of melodies is dissociable from their nonaffective judgment.