Some combinations of musical notes sound pleasing and are termed “consonant,” but others sound unpleasant and are termed “dissonant.” The distinction between consonance and dissonance plays a central role in Western music, and its origins have posed one of the oldest and most debated problems in perception. In modern times, dissonance has been widely believed to be the product of “beating”: interference between frequency components in the cochlea that has been believed to be more pronounced in dissonant than consonant sounds. However, harmonic frequency relations, a higher-order sound attribute closely related to pitch perception, has also been proposed to account for consonance. To tease apart theories of musical consonance, we tested sound preferences in individuals with congenital amusia, a neurogenetic disorder characterized by abnormal pitch perception. We assessed amusics’ preferences for musical chords as well as for the isolated acoustic properties of beating and harmonicity. In contrast to control subjects, amusic listeners showed no preference for consonance, rating the pleasantness of consonant chords no higher than that of dissonant chords. Amusics also failed to exhibit the normally observed preference for harmonic over inharmonic tones, nor could they discriminate such tones from each other. Despite these abnormalities, amusics exhibited normal preferences and discrimination for stimuli with and without beating. This dissociation indicates that, contrary to classic theories, beating is unlikely to underlie consonance. Our results instead suggest the need to integrate harmonicity as a foundation of music preferences, and illustrate how amusia may be used to investigate normal auditory function.
http://www.pnas.org/content/109/48/19858.full.pdf+html
Congenital amusia, often referred to as “tone deafness,” is a neurological condition characterized by a deficit in the perception of pitch and music. While individuals with congenital amusia typically have difficulty recognizing melodies, detecting pitch differences, and distinguishing between consonant and dissonant sounds, research on this condition has provided valuable insights into the basis of musical consonance.
1. **Pitch Perception Deficits**: Individuals with congenital amusia exhibit impairments in pitch perception, making it challenging for them to detect subtle differences in pitch between notes. This difficulty extends to identifying consonant intervals, such as perfect fifths and octaves, which are typically perceived as harmonious due to their simple mathematical ratios.
2. **Sensitivity to Dissonance**: Research has shown that individuals with congenital amusia are less sensitive to dissonant intervals, such as minor seconds and tritones, compared to individuals with typical pitch perception abilities. This suggests that the perception of dissonance may be influenced by neural mechanisms that are impaired in individuals with congenital amusia.
3. **Brain Imaging Studies**: Neuroimaging studies of individuals with congenital amusia have revealed differences in the structure and function of brain regions involved in pitch processing, such as the auditory cortex and inferior frontal gyrus. These findings suggest that congenital amusia may be associated with atypical neural development in areas responsible for processing musical stimuli.
4. **Role of Musical Training**: While congenital amusia is believed to have a genetic basis, research has shown that musical training can influence the severity of pitch perception deficits in individuals with this condition. Some studies have found that individuals with congenital amusia who undergo musical training show improvements in pitch perception and music recognition abilities, although these improvements may be limited compared to individuals without amusia.
Overall, research on congenital amusia has shed light on the neural mechanisms underlying musical consonance and dissonance. By examining how individuals with pitch perception deficits perceive and process musical stimuli, scientists have gained valuable insights into the cognitive and neural processes involved in the perception of harmony and dissonance in music.