Processing of local and global musical information by unilateral brain-damaged patients

Melody processing in unilaterally brain-damaged patients was investigated by manipulating the availability of contour and metre for discrimination in melodies varying, respectively, on the pitch dimension and the temporal dimension. On the pitch dimension, right brain-damaged patients, in contrast to left brain-damaged patients and normal controls, were found to be little affected by the availability of contour as a discrimination cue. However, both brain-damaged groups were impaired on tasks requiring consideration of pitch interval structure. These findings are consistent with hierarchical contribution of the cerebral hemispheres, with the right hemisphere being primary in representing the melody in terms of its global contour and the left hemisphere by filling in the intervallic structure. On the temporal dimension, only the discrimination of durational values (the rhythm) was found to be impaired by a lesion in either hemisphere, which spared, however, the metric interpretation of the musical sequences. These latter results are discussed in the light of current models of temporal processing. Finally, evidence of double dissociation between the processing of the pitch dimension and the processing of rhythm was obtained, providing further support for the need to fractionate musical perceptual abilities in order to arrive at a theory as to how the two hemispheres cohere to produce a musical interpretation of the auditory input.