The "consonance effect" and the hemispheres: a study on a split-brain patient

The association between musical consonance and pleasantness, and between musical dissonance and unpleasantness ("consonance effect") is well established. Furthermore, a number of studies suggest the main involvement of the left hemisphere in the perception of dissonance and that of the right hemisphere in the perception of consonance. In the present study, the consonance effect was studied in a callosotomized patient, D. D. C. and in a control group. In binaural presentations, the patient did not attribute different pleasantness judgements to consonant and dissonant chords, differently from the control group who showed the consonance effect. However, in dichotic presentations (e.g. a chord in one ear and white noise in the other ear), a trend towards the consonance effect was found in D. D. C., but only when chords were presented in his right ear (left hemisphere), whereas the control group confirmed the known hemispheric asymmetry in labelling the pleasantness of consonant and dissonant chords. These results suggest that the right-hemispheric superiority in appreciating consonance might hide the inability of the right hemisphere to classify dissonant chords as unpleasant in the split-brain, whereas the left hemisphere seems capable to differently label the pleasantness of consonant and dissonant chords, even if it is more sensitive to dissonance.