Carrie M. Clancy, B.A., M.M.
Graduate Student, Department of Speech, Language and Hearing Sciences, University of Arizona
Commonly called “tone deafness”, amusia is defined as the inability to recognize or reproduce musical tones. Amusia can be congenital (present at birth) or acquired sometime later in life, as from brain damage due to stroke or injury. General symptoms of amusia include an inability to distinguish pitch in the context of a given tonality (vs. absolute frequency) or rhythm in the context of a given meter (vs. absolute duration), in the absence of peripheral hearing loss or cognitive disorder.
Stewart et al (2006) address three components of normal music listening: music perception, music cognition, and emotional response. They note that “Music, like any sound, is processed in the ascending auditory pathway to the auditory cortex,” which “includes active analysis of the spectro-temporal structure of the stimulus.” Amusia can be considered a central auditory processing disorder due to the associated lack of appropriate music signal processing in both auditory and cognitive realms.
Amusia is divided into pitch and rhythm domains, both of which can have subtle effects on communication in terms of speech and language understanding. As Sihvonen et al (2017, Tracting the Neural Basis of Music) point out, “the ability to perceive emotions conveyed through speech…relies on multiple acoustic cues,” including pitch, intonation, and rhythm. Clark et al (2015) note that “By convention, the definition implies at least some selectivity of the deficit for music” as opposed to speech; “however, the boundaries of amusia as a clinical entity are rather loosely drawn.”
Audiologically, amusic patients present with normal peripheral hearing, including pure tone and speech audiometry. Acquired amusia could occur separately in a patient with a peripheral hearing loss; however, this would complicate the diagnosis. Electrophysiologic CANS testing reveals normal ABR and MLR, with some evidence of abnormal late potential response. Behavioral CANS testing for amusia has not been extensively explored. Diagnosis is typically achieved through behavioral assessment with the Distorted Tune Test (DTT) or the Montreal Battery for Evaluation of Amusia (MBEA).
Both congenital and acquired amusia present functional, quality of life issues for affected patients. Patients with acquired amusia who previously enjoyed playing or listening to music may no longer be able to participate in those activities. Children with congenital amusia may present with pragmatic speech difficulties or may not be responsive to music as a teaching device in educational or therapeutic settings.
Scholarly discussion of amusia dates back to 1871, when Steinthal first used the term “in reference to deficits of musical perception and production following stroke.” (Clark, et al 2015). Shortly thereafter, Allen (1878) described what he called “note-deafness,” or the phenomenon of people who are “incapable of distinguishing in consciousness between the sounds of any two tones lying within the compass of about half an octave (or even more) from one another.” Twentieth century research focused on establishing hemisphere dominance and specific site of lesion for amusia, while more recent studies have distinguished the etiology and pathology of congenital amusia from the acquired form, as well as defining the neural pathways involved in both congenital and acquired amusia.
Congenital amusia is largely idiopathic. Patient medical history is usually unremarkable, as any hearing loss, cognitive disorder, or acquired brain injury would change the diagnosis. The generally accepted prevalence rate is around 4%; however, Pfeifer and Harmann (2015) argue that the “prevalence of congenital amusia is shown to depend highly on the statistical criterion that is applied as cut-off score and on the number of subtests that is considered for the diagnosis.” In 2017, Peretz and Vuvan suggested a revised prevalence rate of 1.5%, as well as reporting a possible hereditary component to congenital amusia, “with 46% of first degree relatives (of amusic subjects) similarly affected” in their study.
The precise pathology of congenital amusia is still under investigation. Hyde et al (2007) found some evidence of “reduced white matter density and abnormal deactivation in the right inferior frontal gyrus, as well as cortical malformations in the right inferior frontal gyrus and auditory cortex.” More recent investigation implicates abnormalities higher in the central auditory pathway, including frontal cortex dysfunction and reduced connectivity between the auditory cortex and frontotemporal cortex (Chen & Yuan, 2016). Moreau et al (2013) found normal mismatch negativity (MMN) response in amusic subjects, but absent P3b response to small pitch changes, concluding “that the amusic brain responds to small pitch differences at a pre-attentive level of perception, but is unable to detect consciously those same pitch deviances at a later attentive level.”
Incidence of acquired amusia following brain injury is much higher than for congenital amusia. Sihvonen (2016) estimates incidence from 35-69% after middle cerebral artery stroke in either hemisphere. Patient medical history will include a specific incident, such as stroke or injury, and site of lesion can often be visualized through radiologic imaging. Medical management involves addressing the cause of the damage and treatment of immediate symptoms, which may delay assessment for amusia.
Sihvonen’s 2016 study ‘Neural basis of acquired amusia and its recovery after stroke’ found that acquired amusia appears to stem from damage to the right superior temporal gyrus, Heschl’s gyrus, insula, and striatum, but he notes that overall study findings “regarding lesion lateralization (left/right) and type of musical deficit have been mixed.” Individual case studies have shown that amusia can also follow left hemisphere damage, due to differences in music processing between experienced musicians and non-musicians, with experienced musicians processing predominantly in the left hemisphere and non-musicians primarily in the right (Bever and Chiarello, 1974). Peretz (1990) further found that general melodic features such as overall contour and shape are processed in the right hemisphere, while the left hemisphere processes finer details, such as the specific intervallic structure of a melody. As suggested above for congenital amusia, a 1990 case study of acquired amusia by Tramo et al theorizes that “sensory, perceptual, and cognitive functions mediating tonal information processing in music are neurologically dissociable” and that those cognitive functions do not necessarily depend on the integrity of the auditory cortex.
Audiologists should consider patient desires and functional implications in devising treatment strategies for amusia. Audiologic management may involve explicit auditory training for detecting relative changes in frequency and duration. For patients hoping to regain previous musical abilities or enjoyment of music, singing lessons with a qualified voice teacher or music therapy might be appropriate. In cases involving pragmatic speech difficulties, referral to a speech-language pathologist might be warranted. Amusia presents a unique opportunity for professionals across related fields, including neurology, audiology, speech pathology, and music, to network and develop effective diagnostic and treatment practices.
Part 2 of this article will examine current and future research implications for both congenital and acquired amusia. Topics of concern include refinements in diagnosis and prevalence reporting, physiologic and behavioral assessment procedures, further breakdown of the pitch and rhythm domains, and the interaction among genes, environment, and behavior with regard to music.
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Editor’s Note: Carrie Clancy is a graduate student in Audiology at the University of Arizona. She has received Bachelor of Arts degrees in Music and Speech-Language Pathology/Audiology and a Master of Music degree from the University of Nebraska. She will begin the Au.D. program at the University of Arizona in Fall 2018.