Cortical deafness to dissonance

Ordinary listeners, including infants, easily distinguish consonant from di ssonant pitch combinations and consider the former more pleasant than the l atter. The preference for consonance over dissonance was tested in a patien t, I.R., who suffers from music perception and memory disorders as a result of bilateral lesions to the auditory cortex. In Experiment 1, I.R. was fou nd to be unable to distinguish consonant from dissonant versions of musical excerpts taken from the classical repertoire by rating their pleasantness. I.R.'s indifference to dissonance was not due to a loss of all affective r esponses to music, however, since she rated the same excerpts as happy or s ad, as normal controls do. In Experiment 2, I.R.'s lack of responsiveness t o varying degrees of dissonance was replicated with chord sequences which h ad been used in a previous study using PET, in examining emotional response s to dissonance, A CT scan of I.R.'s brain was co-registered with the PET a ctivation data from normal volunteers. Comparison of I.R.'s scan with the P ET data revealed that the damaged areas overlapped with the regions identif ied to be involved in the perceptual analysis of the musical input, but not with the paralimbic regions involved in affective responses. Taken togethe r, the findings suggest that dissonance may be computed bilaterally in the superior temporal gyri by specialized mechanisms prior to its emotional int erpretation.