Discrimination and recognition of tonal melodies after unilateral cerebral excisions.

Groups of surgical patients with unilateral temporal- or frontal-lobe lesions and normal control subjects were tested in melodic discrimination and recognition tasks. The discrimination task required detection of a single-note change in a pair of short unfamiliar tonal melodies. The altered note either violated or preserved the contour, the scale, or both, of the original melody. Recognition required that the melodies used in the discrimination task be recognized from among a set of similar foils. Right temporal-lobe patients performed most poorly in discrimination. Further analysis showed that excision of the primary auditory receiving area. Heschl's gyri from either side resulted in a deficit which was independent from, but additive with, the deficit caused by right temporal lobectomy. In the recognition task, both temporal-lobe groups were impaired as compared to control. The use of scale and contour cues was similar for all groups, indicating that the deficits observed are not attributable to failure to process one of these cues. Right frontal-lobe lesioned patients differed from the others in response bias, but performed as well as controls on both tasks. The results are interpreted as evidence for two processes in melodic discrimination, one due to short-term memory mechanisms, the other attributable to a deficit in processing complex auditory patterns.