Exploring variants of amusia: tone deafness, rhythm impairment, and intonation insensitivity

The term congenital amusia describes a disorder of music processing that cannot readily be explained by acquired brain injury or other environmental factors. Cases of congenital amusia in the absence of other processing difficulties imply that there are music-specific neural networks that can be selectively compromised by a congenital anomaly. Research on amusia has identified individuals with impaired pitch and temporal aspects of music, as well as individuals who have selective difficulties with the pitch dimension of music. Some evidence suggests that these deficits are specific to music. For example, individuals with difficulties in musical pitch processing can differentiate questions and statements among spoken phrases that vary in intonation (pitch variation) but are otherwise identical. This paper further examines the question of whether amusia is restricted to impairment on the pitch dimension of music. The logic behind two studies conducted in our laboratory is described, along with preliminary results. In one study, a form of rhythm impairment was identified in which individuals suffer from a disproportionate impairment on the rhythmic dimension of music with no impairment on pitch-related tasks. In another study, individuals with pitch-related amusia performed worse than unimpaired individuals on tests of sensitivity to emotional prosody. The latter evidence suggests that impairments associated with amusia may not be restricted to music, but may reflect a deficit at a stage of auditory processing that is relevant to music and speech.