Amusia
Encyclopedia
Amusia is a musical disorder that appears mainly as a defect in processing pitch, but it also encompasses musical memory and recognition. Two main classifications of amusia exist: acquired amusia, which occurs as a result of brain damage, and congenital amusia, which results from a music processing anomaly at birth.
Studies have shown that congenital amusia is a deficit in fine-grained pitch discrimination and that 4% of the population suffers from this disorder. Acquired amusia, on the other hand, may take several forms. Patients with brain damage may experience the loss of ability to produce musical sounds while sparing speech, much like aphasics lose speech selectively but can sometimes still sing. Other forms of amusia may affect specific sub-processes of music processing. Current research has demonstrated dissociations
between rhythm, melody and emotional processing of music, and amusia may include impairment of any combination of these skill sets.
. Also, infants are able to differentiate between consonant and dissonant
intervals. These perceptual skills indicate that music-specific predispositions exist.
Prolonged exposure to music develops and refines these skills. Extensive musical training does not seem to be necessary in the processing of chords
and keys
. The development of musical competence most likely depends on the encoding of pitch along musical scales and maintaining a regular pulse, both of which are key components in the structure of music and aid in perception, memory, and performance. Also, the encoding of pitch and temporal regularity are both likely to be specialized for music processing. Pitch perception is absolutely crucial to processing music. The use of scales and the organization of scale tones around a central tone (called the tonic
) assign particular importance to notes in the scale and cause non-scale notes to sound out of place. This enables the listener to ascertain when a wrong note is played. However, in individuals with amusia, this ability is either compromised or lost entirely.
Music-specific neural networks exist in the brain for a variety of music-related tasks. It has been shown that Broca's area
is involved in the processing of musical syntax. Furthermore, brain damage can disrupt an individual's ability to tell the difference between tonal and atonal music and detect the presence of wrong notes, but can preserve the individual's ability to assess the distance between pitches and the direction of the pitch. The opposite scenario can also occur, in which the individual loses pitch discrimination capabilities, but can sense and appreciate the tonal context of the work. Distinct neural networks also exist for music memories, singing, and music recognition. Neural networks for music recognition are particularly intriguing. A patient can undergo brain damage that renders him/her unable to recognize familiar melodies that are presented without words. However, the patient maintains the ability to recognize spoken lyrics or words, familiar voices, and environmental sounds. The reverse case is also possible, in which the patient cannot recognize spoken words, but can still recognize familiar melodies. These situations overturn previous claims that speech recognition and music recognition share a single processing system. Instead, it is clear that there are at least two distinct processing modules: one for speech and one for music.
, and the inability to detect wrong or out-of tune notes. Clinical, or expressive, symptoms include the loss of ability to sing, write musical notation
, and/or play an instrument. A mixed disorder would be a combination of expressive and receptive impairment.
Clinical symptoms of acquired amusia are much more variable than those of congenital amusia and are determined by the location and nature of the lesion. Brain injuries may afflict motor or expressive functioning, including the ability to sing, whistle, or hum a tune (oral-expressive amusia), the ability to play an instrument (instrumental amusia or musical apraxia), and the ability to write music (musical agraphia). Additionally, brain damage to the receptive dimension affects the faculty to discriminate tunes (receptive or sensorial amusia), the ability to read music (musical alessia), and the ability to identify songs that were familiar prior to the brain damage (amnesic amusia).
Research suggests that patients with amusia also have difficulty when it comes to spatial processing. Amusics performed more quickly than normal individuals on a combined task of both spatial and musical processing tasks, which is most likely due to their deficit. Normal individuals experience interference due to their intact processing of both musical and spatial tasks, while amusics do not. Pitch processing normally depends on the cognitive mechanisms that are usually used to process spatial representations.
Those with congenital amusia show impaired performance on discrimination, identification and imitation of sentences with intonational
differences in pitch direction in their final word. This suggests that amusia can in subtle ways impair language processing.
, musical scales, pitch interval
s, rhythm
, meter, and memory. An individual is considered amusic if he/she performs two standard deviations below the mean obtained by musically-competent controls. This musical pitch disorder represents a phenotype that serves to identify the associated neuro-genetic factors. Both MRI-based brain structural analyses and electroencephalography (EEG) are common methods employed to uncover brain anomalies associated with amusia (See Neuroanatomy
). Additionally, voxel-based morphometry (VBM) is used to detect anatomical differences between the MRIs of amusic brains and musically intact brains, specifically with respect increased and/or decreased amounts of white and grey matter.
, refers to a musical disability that cannot be explained by prior brain lesion, hearing loss, cognitive defects, or lack of environmental stimulation, and it affects about 4% of the population. Individuals who suffer from congenital amusia seem to lack the musical predispositions that most people are born with. They are unable to recognize or hum familiar tunes even though they have normal audiometry
and above average intellectual and memory skills. Also, they do not show sensitivity to dissonant chords in a melodic context, which, as discussed earlier, is one of the musical predispositions exhibited by infants. The hallmark of congenital amusia is a deficit in fine-grained pitch discrimination, and this deficit is most apparent when congenital amusics are asked to pick out a wrong note in a given melody. If the distance between two successive pitches is small, congenital amusics are not able to detect a pitch change. As a result of this defect in pitch perception, a lifelong musical impairment may emerge due to a failure to internalize musical scales. A lack of fine-grained pitch discrimination makes it extremely difficult for amusics to enjoy and appreciate music, which consists largely of small pitch changes.
(MCA) infarction one week, three months, and six months after the stroke occurred. Amusic subjects were identified one week following their stroke, and over the course of the study, amusics and non-amusics were compared in both brain lesion location and their performances on neuropsychological tests.
Results showed that there was no significant difference in the distribution of left and right hemisphere lesions between amusic and non-amusic groups, but that the amusic group had a significantly higher number of lesions to the frontal lobe
and auditory cortex. Temporal lobe
lesions were also observed in patients with amusia. Amusia is a common occurrence following an ischemic MCA stroke, as evidenced by the 60% of patients who were found to be amusic at the one week post-stroke stage. While significant recovery takes place over time, amusia can persist for long periods of time. Test results suggest that acquired amusia and its recovery in the post-stroke stage are associated with a variety of cognitive functions, particularly attention, executive functioning, and working memory.
, secondary auditory cortex, and limbic system
are responsible for this faculty, while more recent studies suggest that lesions in other cortical areas, abnormalities in cortical thickness, and deficiency in neural connectivity and brain plasticity may contribute to amusia. While various etiologies of amusia exist, some general findings that provide insight to the brain mechanisms involved in music processing are discussed below.
(pitch direction) and interval (frequency ratio between successive notes) information. The right superior temporal gyrus recruits and evaluates contour information, while both right and left temporal regions recruit and evaluate interval information. In addition, the right anterolateral part of Heschl's gyrus (primary auditory cortex) is also concerned with processing pitch information.
. While not studied as thoroughly as language, music and visual processing were also studied. In 1888-1890, August Knoblauch produced a cognitive model for music processing and termed it amusia. This model for music processing was the earliest produced.
In order to determine if Monica's disorder is amusia, she was subjected to the MBEA series of tests. One of the tests dealt with Monica's difficulties in discriminating pitch variations in sequential notes. In this test, a pair of melodies was played, and Monica was asked if the second melody in the pair contained a wrong note. Monica's score on this test was well below the average score generated by the control group. Further tests showed that Monica struggles with recognizing highly familiar melodies, but that she has no problems in recognizing the voices of well-known speakers. Thus, it appears that Monica's deficit seems limited to music. Interestingly, a later study showed that not only do amusics experience difficulty in discriminating variations in pitch, but they also exhibit deficits in perceiving patterns in pitch.
This finding led to another test that was designed to assess the presence of a deficiency in pitch perception. In this test, Monica heard a sequence of five piano tones of constant pitch followed by a comparison sequence of five piano tones in which the fourth tone could be the same pitch as the other notes in the sequence or a completely different pitch altogether. Monica was asked to respond "yes" if she detected a pitch change on the fourth tone or respond "no" if she could not detect a pitch change. Results show that Monica could barely detect a pitch change as large as two semitones, or half steps. While this pitch-processing deficit is extremely severe, it does not seem to include speech intonation. This is because pitch variations in speech are very coarse compared with those used in music. In conclusion, Monica's learning disability arises from a basic problem in pitch discrimination, which is viewed as the origin of congenital amusia.
Overall, test results support the view that congenital amusia is hereditary. It is likely to be influenced by several genes that interact to increase an individual's susceptibility to its development. However, the fact that the offspring have a lower risk of developing congenital amusia shows that it can be less prevalent when the musical environment is enriched. This stresses the importance that experience-dependent tuning has in the musical pitch system.
s that were written in the music. However, many of the amusic testing subjects were able to sing with the correct rhythm
. The results confirmed that the amusics' ability to detect pitch changes influences their level of singing proficiency. The subjects who struggled the most with pitch perception were the most unstable in producing the correct pitch and made several pitch interval and contour
errors. However, there were some remarkable exceptions. A couple of amusic individuals were able to sing proficiently despite extremely impaired pitch perception.
It is also interesting to compare the results of singing with the lyrics and singing on the syllable "la". Although most of the amusic subjects struggled with maintaining the correct pitch when singing with lyrics, they were able to complete the task. However, when singing the same song on the syllable "la", more than half of the amusic subjects could only sing a few notes. This is due to a poor memory of the musical component of songs. Overall, it was concluded that singing deficiency in amusic individuals might be a result of their pitch perception deficit. However, the existence of amusic individuals who are able to sing proficiently suggests that there may be separate neural pathways for auditory perception and action.
and other similar disorders. Research has been shown that amusia may be related to an increase in size of the cerebral cortex
, which may be a result of a malformation in cortical development. Diseases such as dyslexia
and epilepsy
are due to a malformation in cortical development and also lead to an increase in cortical thickness, which leads researchers to believe that congenital amusia may be caused by the identical phenomenon in a different area of the brain.
Amusia is also similar to aphasia
in that they affect similar areas of the brain
near the temporal lobe
. Most cases of those with amusia do not show any symptoms of aphasia. However, a number of cases have shown that those who have aphasia can exhibit symptoms of amusia, especially in acquired aphasia. The two are not mutually exclusive and having one does not imply possession of the other. In acquired amusia, inability to perceive music correlates with an inability to perform other higher-level functions. As musical ability improves, so too do the higher cognitive functions which suggests that musical ability is closely related to these higher-level functions, such as memory
and learning
, mental flexibility, and semantic fluency.
Amusia can also be related to aprosody
, a disorder in which the sufferer's speech is affected, becoming extremely monotonous. It has been found that both amusia and aprosody can arise from seizures occurring in the non-dominant hemisphere. They can also both arise from lesions to the brain, as can Broca's aphasia come about simultaneously with amusia from injury. There is a relation between musical abilities and the components of speech, however, they are not understood very well.
, the rest of an amusic's brain remains normal. The only effect is on the ability to tell different notes apart due to the separation of two key areas in the brain. Most sufferers of amusia describe music as unpleasant. Others simply refer to it as noise and find it annoying. This can have social implications because amusics often try to avoid music, which in many social situations is not an option. In China
and other countries in which identical words have different meanings based on pitch, amusia may have a much more pronounced social and emotional impact; difficulty in speaking and understanding the language.
.
Studies have shown that congenital amusia is a deficit in fine-grained pitch discrimination and that 4% of the population suffers from this disorder. Acquired amusia, on the other hand, may take several forms. Patients with brain damage may experience the loss of ability to produce musical sounds while sparing speech, much like aphasics lose speech selectively but can sometimes still sing. Other forms of amusia may affect specific sub-processes of music processing. Current research has demonstrated dissociations
Dissociation (neuropsychology)
In neuropsychology, dissociation involves identifying the neural substrate of a particular brain function through identification of case studies, neuroimaging, or neuropsychological testing.-Single dissociation:...
between rhythm, melody and emotional processing of music, and amusia may include impairment of any combination of these skill sets.
Basics of music processing
Neurologically intact individuals appear to be born musical. Even before they are able to talk, infants show remarkable musical abilities that are similar to those of adults in that they are sensitive to musical scales and a regular tempoTempo
In musical terminology, tempo is the speed or pace of a given piece. Tempo is a crucial element of any musical composition, as it can affect the mood and difficulty of a piece.-Measuring tempo:...
. Also, infants are able to differentiate between consonant and dissonant
Consonance and dissonance
In music, a consonance is a harmony, chord, or interval considered stable, as opposed to a dissonance , which is considered to be unstable...
intervals. These perceptual skills indicate that music-specific predispositions exist.
Prolonged exposure to music develops and refines these skills. Extensive musical training does not seem to be necessary in the processing of chords
Chord (music)
A chord in music is any harmonic set of two–three or more notes that is heard as if sounding simultaneously. These need not actually be played together: arpeggios and broken chords may for many practical and theoretical purposes be understood as chords...
and keys
Key (music)
In music theory, the term key is used in many different and sometimes contradictory ways. A common use is to speak of music as being "in" a specific key, such as in the key of C major or in the key of F-sharp. Sometimes the terms "major" or "minor" are appended, as in the key of A minor or in the...
. The development of musical competence most likely depends on the encoding of pitch along musical scales and maintaining a regular pulse, both of which are key components in the structure of music and aid in perception, memory, and performance. Also, the encoding of pitch and temporal regularity are both likely to be specialized for music processing. Pitch perception is absolutely crucial to processing music. The use of scales and the organization of scale tones around a central tone (called the tonic
Tonic (music)
In music, the tonic is the first scale degree of the diatonic scale and the tonal center or final resolution tone. The triad formed on the tonic note, the tonic chord, is thus the most significant chord...
) assign particular importance to notes in the scale and cause non-scale notes to sound out of place. This enables the listener to ascertain when a wrong note is played. However, in individuals with amusia, this ability is either compromised or lost entirely.
Music-specific neural networks exist in the brain for a variety of music-related tasks. It has been shown that Broca's area
Broca's area
Broca's area is a region of the hominid brain with functions linked to speech production.The production of language has been linked to the Broca’s area since Pierre Paul Broca reported impairments in two patients. They had lost the ability to speak after injury to the posterior inferior frontal...
is involved in the processing of musical syntax. Furthermore, brain damage can disrupt an individual's ability to tell the difference between tonal and atonal music and detect the presence of wrong notes, but can preserve the individual's ability to assess the distance between pitches and the direction of the pitch. The opposite scenario can also occur, in which the individual loses pitch discrimination capabilities, but can sense and appreciate the tonal context of the work. Distinct neural networks also exist for music memories, singing, and music recognition. Neural networks for music recognition are particularly intriguing. A patient can undergo brain damage that renders him/her unable to recognize familiar melodies that are presented without words. However, the patient maintains the ability to recognize spoken lyrics or words, familiar voices, and environmental sounds. The reverse case is also possible, in which the patient cannot recognize spoken words, but can still recognize familiar melodies. These situations overturn previous claims that speech recognition and music recognition share a single processing system. Instead, it is clear that there are at least two distinct processing modules: one for speech and one for music.
Symptoms
Symptoms of amusia are generally categorized as receptive, clinical, or mixed. Symptoms of receptive amusia, sometimes referred to as "musical deafness", include the inability to recognize familiar melodies, the loss of ability to read musical notationMusical notation
Music notation or musical notation is any system that represents aurally perceived music, through the use of written symbols.-History:...
, and the inability to detect wrong or out-of tune notes. Clinical, or expressive, symptoms include the loss of ability to sing, write musical notation
Musical notation
Music notation or musical notation is any system that represents aurally perceived music, through the use of written symbols.-History:...
, and/or play an instrument. A mixed disorder would be a combination of expressive and receptive impairment.
Clinical symptoms of acquired amusia are much more variable than those of congenital amusia and are determined by the location and nature of the lesion. Brain injuries may afflict motor or expressive functioning, including the ability to sing, whistle, or hum a tune (oral-expressive amusia), the ability to play an instrument (instrumental amusia or musical apraxia), and the ability to write music (musical agraphia). Additionally, brain damage to the receptive dimension affects the faculty to discriminate tunes (receptive or sensorial amusia), the ability to read music (musical alessia), and the ability to identify songs that were familiar prior to the brain damage (amnesic amusia).
Research suggests that patients with amusia also have difficulty when it comes to spatial processing. Amusics performed more quickly than normal individuals on a combined task of both spatial and musical processing tasks, which is most likely due to their deficit. Normal individuals experience interference due to their intact processing of both musical and spatial tasks, while amusics do not. Pitch processing normally depends on the cognitive mechanisms that are usually used to process spatial representations.
Those with congenital amusia show impaired performance on discrimination, identification and imitation of sentences with intonational
Intonation (linguistics)
In linguistics, intonation is variation of pitch while speaking which is not used to distinguish words. It contrasts with tone, in which pitch variation does distinguish words. Intonation, rhythm, and stress are the three main elements of linguistic prosody...
differences in pitch direction in their final word. This suggests that amusia can in subtle ways impair language processing.
Diagnosis
The diagnosis of amusia requires individuals to detect out-of-key notes in conventional but unfamiliar melodies. A behavioral failure on this test is diagnostic because there is typically no overlap between the distributions of the scores of amusics and controls. Such scores are generally obtained through the Montreal Battery of Evaluation of Amusia (MBEA), which involves a series of tests that evaluate the use of musical characteristics known to contribute to the memory and perception of conventional music. The battery comprises six subtests which assess the ability to discriminate pitch contourPitch contour
In linguistics, speech synthesis, and music, the pitch contour of a sound is a function or curve that tracks the perceived pitch of the sound over time....
, musical scales, pitch interval
Interval (music)
In music theory, an interval is a combination of two notes, or the ratio between their frequencies. Two-note combinations are also called dyads...
s, rhythm
Rhythm
Rhythm may be generally defined as a "movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions." This general meaning of regular recurrence or pattern in time may be applied to a wide variety of cyclical natural phenomena having a periodicity or...
, meter, and memory. An individual is considered amusic if he/she performs two standard deviations below the mean obtained by musically-competent controls. This musical pitch disorder represents a phenotype that serves to identify the associated neuro-genetic factors. Both MRI-based brain structural analyses and electroencephalography (EEG) are common methods employed to uncover brain anomalies associated with amusia (See Neuroanatomy
Neuroanatomy
Neuroanatomy is the study of the anatomy and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defined nervous systems, and thus we can begin to speak of...
). Additionally, voxel-based morphometry (VBM) is used to detect anatomical differences between the MRIs of amusic brains and musically intact brains, specifically with respect increased and/or decreased amounts of white and grey matter.
Classifications
There are two general classifications of amusia: congenital amusia and acquired amusia.Congenital amusia
Congenital amusia, commonly known as tone deafnessTone deafness
Tone deafness is the lack of relative pitch, or the inability to distinguish between musical notes that is not due to the lack of musical training or education...
, refers to a musical disability that cannot be explained by prior brain lesion, hearing loss, cognitive defects, or lack of environmental stimulation, and it affects about 4% of the population. Individuals who suffer from congenital amusia seem to lack the musical predispositions that most people are born with. They are unable to recognize or hum familiar tunes even though they have normal audiometry
Audiometry
Audiometry is the testing of hearing ability, involving thresholds and differing frequencies. Typically, audiometric tests determine a subject's hearing levels with the help of an audiometer, but may also measure ability to discriminate between different sound intensities, recognize pitch, or...
and above average intellectual and memory skills. Also, they do not show sensitivity to dissonant chords in a melodic context, which, as discussed earlier, is one of the musical predispositions exhibited by infants. The hallmark of congenital amusia is a deficit in fine-grained pitch discrimination, and this deficit is most apparent when congenital amusics are asked to pick out a wrong note in a given melody. If the distance between two successive pitches is small, congenital amusics are not able to detect a pitch change. As a result of this defect in pitch perception, a lifelong musical impairment may emerge due to a failure to internalize musical scales. A lack of fine-grained pitch discrimination makes it extremely difficult for amusics to enjoy and appreciate music, which consists largely of small pitch changes.
Acquired amusia
Acquired amusia is a musical disability that shares the same characteristics as congenital amusia, but rather than being inherited, it is the result of brain damage. It is also more common than congenital amusia. While it has been suggested that music is processed by music-specific neural networks in the brain, this view has been broadened to show that music processing also encompasses generic cognitive functions, such as memory, attention, and executive processes. A recent study was conducted to investigate the neural and cognitive mechanisms that underlie acquired amusia and contribute to its recovery. The study was performed on 53 stroke patients with a left or right hemisphere middle cerebral arteryMiddle cerebral artery
-External links:*...
(MCA) infarction one week, three months, and six months after the stroke occurred. Amusic subjects were identified one week following their stroke, and over the course of the study, amusics and non-amusics were compared in both brain lesion location and their performances on neuropsychological tests.
Results showed that there was no significant difference in the distribution of left and right hemisphere lesions between amusic and non-amusic groups, but that the amusic group had a significantly higher number of lesions to the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
and auditory cortex. Temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
lesions were also observed in patients with amusia. Amusia is a common occurrence following an ischemic MCA stroke, as evidenced by the 60% of patients who were found to be amusic at the one week post-stroke stage. While significant recovery takes place over time, amusia can persist for long periods of time. Test results suggest that acquired amusia and its recovery in the post-stroke stage are associated with a variety of cognitive functions, particularly attention, executive functioning, and working memory.
Overview
Many research studies of individuals with amusia show that a number of cortical regions appear to be involved in processing music. Some report that the primary auditory cortexPrimary auditory cortex
The primary auditory cortex is the region of the brain that is responsible for the processing of auditory information. Corresponding roughly with Brodmann areas 41 and 42, it is located on the temporal lobe, and performs the basics of hearing—pitch and volume...
, secondary auditory cortex, and limbic system
Limbic system
The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix, which seemingly support a variety of functions including emotion, behavior, long term memory, and olfaction. The term "limbic" comes from the Latin...
are responsible for this faculty, while more recent studies suggest that lesions in other cortical areas, abnormalities in cortical thickness, and deficiency in neural connectivity and brain plasticity may contribute to amusia. While various etiologies of amusia exist, some general findings that provide insight to the brain mechanisms involved in music processing are discussed below.
Pitch relations
Studies suggest that the analysis of pitch is primarily controlled by the right temporal region of the brain. The right secondary auditory cortex processes pitch change and manipulation of fine tunes; specifically, this region distinguishes the multiple pitches that characterize melodic tunes as contourPitch contour
In linguistics, speech synthesis, and music, the pitch contour of a sound is a function or curve that tracks the perceived pitch of the sound over time....
(pitch direction) and interval (frequency ratio between successive notes) information. The right superior temporal gyrus recruits and evaluates contour information, while both right and left temporal regions recruit and evaluate interval information. In addition, the right anterolateral part of Heschl's gyrus (primary auditory cortex) is also concerned with processing pitch information.
Temporal relations
The brain analyzes the temporal (rhythmic) components of music in two ways: (1) it segments the ongoing sequences of music into temporal events based on duration, and (2) it groups those temporal events to understand the underlying beat to music. Studies on rhythmic discrimination reveal that the right temporal auditory cortex is responsible for temporal segmenting, and the left temporal auditory cortex is responsible for temporal grouping. Other studies suggest the participation of motor cortical areas in rhythm perception and production. Therefore, a lack of involvement and networking between bilateral temporal cortices and neural motor centers may contribute to both congenital and acquired amusia.Memory
Memory is required in order to process and integrate both melodic and rhythmic aspects of music. Studies suggest that there is a rich interconnection between the right temporal gyrus and frontal cortical areas for working memory in music appreciation. This connection between the temporal and frontal regions of the brain is extremely important since these regions play critical roles in music processing. Changes in the temporal areas of the amusic brain are most likely associated with deficits in pitch perception and other musical characteristics, while changes in the frontal areas are potentially related to deficits in cognitive processing aspects, such as memory, that are needed for musical discrimination tasks. Memory is also concerned with the recognition and internal representation of tunes, which help to identify familiar songs and confer the ability to sing tunes in one's head. The activation of the superior temporal region and left inferior temporal and frontal areas is responsible for the recognition of familiar songs, and the right auditory cortex (a perceptual mechanism) is involved in the internal representation of tunes. These findings suggest that any abnormalities and/or injuries to these regions of the brain could facilitate amusia.Other regions of the brain possibly linked to amusia
- Lesions (or the absence of) in associations between the right temporal lobe and inferior frontal lobe
- Cortical thickness and reduced white matter – in a recent study, voxel-based morphometry, an imaging technique used to explore structural differences in the brain, revealed a decrease in white matterWhite matterWhite matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
concentration in the right inferior frontal gyrusInferior frontal gyrusThe inferior frontal gyrus is a gyrus of the frontal lobe . It is labelled gyrus frontalis inferior, its Latin name...
of amusic individuals as compared to controls. Lack of extensive exposure to music could be a contributing factor to this white matterWhite matterWhite matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
reduction. For example, amusic individuals may be less inclined to listen to music than others, which could ultimately cause reduced myelination of connections to the frontal areas of the brain. - Involvement of the parahippocampal gyrus (responsible for the emotional reaction to music)
Discovery
In 1825, F. Gall mentioned a "musical organ" in a specific region of the human brain that could be spared or disrupted after a traumatic event resulting in brain damage. In 1865, Jean-Baptiste Bouillaud described the first series of cases that involved the loss of music abilities that were due to brain injury. Later, during the late nineteenth-century, several influential neurologists studied language in an attempt to construct a theory of cognitionTheory of cognitive development
Piaget's theory of cognitive development is a comprehensive theory about the nature and development of human intelligence first developed by Jean Piaget. It is primarily known as a developmental stage theory, but in fact, it deals with the nature of knowledge itself and how humans come gradually to...
. While not studied as thoroughly as language, music and visual processing were also studied. In 1888-1890, August Knoblauch produced a cognitive model for music processing and termed it amusia. This model for music processing was the earliest produced.
First documented case of congenital amusia
While the possibility that certain individuals may be born with musical deficits is not a new notion, the first documented case of congenital amusia was published relatively recently. The study was conducted with a female volunteer, referred to as Monica, who declared herself to be musically impaired in response to an advertisement in the newspaper. Monica had no psychiatric or neurological history, nor did she have any hearing loss. MRI scans showed no abnormalities. Monica also scored above average on a standard intelligence test, and her working memory was evaluated and found to be normal. However, Monica suffers from a lifelong inability to recognize or perceive music, which has persisted even after involvement with music through church choir and band during her childhood and teenage years. Monica even admits that she does not enjoy listening to music because, to her, it sounds like noise and evokes a stressful response.In order to determine if Monica's disorder is amusia, she was subjected to the MBEA series of tests. One of the tests dealt with Monica's difficulties in discriminating pitch variations in sequential notes. In this test, a pair of melodies was played, and Monica was asked if the second melody in the pair contained a wrong note. Monica's score on this test was well below the average score generated by the control group. Further tests showed that Monica struggles with recognizing highly familiar melodies, but that she has no problems in recognizing the voices of well-known speakers. Thus, it appears that Monica's deficit seems limited to music. Interestingly, a later study showed that not only do amusics experience difficulty in discriminating variations in pitch, but they also exhibit deficits in perceiving patterns in pitch.
This finding led to another test that was designed to assess the presence of a deficiency in pitch perception. In this test, Monica heard a sequence of five piano tones of constant pitch followed by a comparison sequence of five piano tones in which the fourth tone could be the same pitch as the other notes in the sequence or a completely different pitch altogether. Monica was asked to respond "yes" if she detected a pitch change on the fourth tone or respond "no" if she could not detect a pitch change. Results show that Monica could barely detect a pitch change as large as two semitones, or half steps. While this pitch-processing deficit is extremely severe, it does not seem to include speech intonation. This is because pitch variations in speech are very coarse compared with those used in music. In conclusion, Monica's learning disability arises from a basic problem in pitch discrimination, which is viewed as the origin of congenital amusia.
Family aggregation study
Another interesting question posed about congenital amusia is if it has a genetic origin. A study was conducted to test for the presence of a genetic origin by studying family aggregation of congenital amusia. Family members of amusics were studied, as well as family members of a control group. The study yielded interesting results. Amusia cannot be attributed solely to family environment due to the presence of at least one unaffected sibling in each tested family in the amusic group. Also, music was found to be present to a lesser extent, but not absent, in the environment of the amusic subjects than in that of the musically intact control group. This supports the claim that the occurrence of congenital amusia cannot be explained by a lack of environmental stimulation. Another interesting finding was that the next generation, or the offspring of those with congenital amusia, was more musical. A reason for this might be that musical stimulation for the offspring probably started early in life when their brains were more plastic.Overall, test results support the view that congenital amusia is hereditary. It is likely to be influenced by several genes that interact to increase an individual's susceptibility to its development. However, the fact that the offspring have a lower risk of developing congenital amusia shows that it can be less prevalent when the musical environment is enriched. This stresses the importance that experience-dependent tuning has in the musical pitch system.
Singing in congenital amusia
While it is known that congenital amusia is a disorder characterized by poor pitch perception, a recent study sought to discover to what extent this pitch deficit may compromise singing. In this study, eleven amusic individuals and eleven controls were asked to sing a familiar song using the lyrics first, and then using the syllable "la". Results showed that individuals with congenital amusia were poor singers. They could not maintain a stable pitch, nor could they sing the correct pitch intervalInterval (music)
In music theory, an interval is a combination of two notes, or the ratio between their frequencies. Two-note combinations are also called dyads...
s that were written in the music. However, many of the amusic testing subjects were able to sing with the correct rhythm
Rhythm
Rhythm may be generally defined as a "movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions." This general meaning of regular recurrence or pattern in time may be applied to a wide variety of cyclical natural phenomena having a periodicity or...
. The results confirmed that the amusics' ability to detect pitch changes influences their level of singing proficiency. The subjects who struggled the most with pitch perception were the most unstable in producing the correct pitch and made several pitch interval and contour
Pitch contour
In linguistics, speech synthesis, and music, the pitch contour of a sound is a function or curve that tracks the perceived pitch of the sound over time....
errors. However, there were some remarkable exceptions. A couple of amusic individuals were able to sing proficiently despite extremely impaired pitch perception.
It is also interesting to compare the results of singing with the lyrics and singing on the syllable "la". Although most of the amusic subjects struggled with maintaining the correct pitch when singing with lyrics, they were able to complete the task. However, when singing the same song on the syllable "la", more than half of the amusic subjects could only sing a few notes. This is due to a poor memory of the musical component of songs. Overall, it was concluded that singing deficiency in amusic individuals might be a result of their pitch perception deficit. However, the existence of amusic individuals who are able to sing proficiently suggests that there may be separate neural pathways for auditory perception and action.
Related diseases
Amusia has recently been classified as a learning disability that affects musical abilities. Research suggests that in congenital amusia, younger subjects can be taught tone differentiation techniques. This finding leads researchers to believe that amusia is related to dyslexiaDyslexia
Dyslexia is a very broad term defining a learning disability that impairs a person's fluency or comprehension accuracy in being able to read, and which can manifest itself as a difficulty with phonological awareness, phonological decoding, orthographic coding, auditory short-term memory, or rapid...
and other similar disorders. Research has been shown that amusia may be related to an increase in size of the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
, which may be a result of a malformation in cortical development. Diseases such as dyslexia
Dyslexia
Dyslexia is a very broad term defining a learning disability that impairs a person's fluency or comprehension accuracy in being able to read, and which can manifest itself as a difficulty with phonological awareness, phonological decoding, orthographic coding, auditory short-term memory, or rapid...
and epilepsy
Epilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
are due to a malformation in cortical development and also lead to an increase in cortical thickness, which leads researchers to believe that congenital amusia may be caused by the identical phenomenon in a different area of the brain.
Amusia is also similar to aphasia
Aphasia
Aphasia is an impairment of language ability. This class of language disorder ranges from having difficulty remembering words to being completely unable to speak, read, or write....
in that they affect similar areas of the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
near the temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
. Most cases of those with amusia do not show any symptoms of aphasia. However, a number of cases have shown that those who have aphasia can exhibit symptoms of amusia, especially in acquired aphasia. The two are not mutually exclusive and having one does not imply possession of the other. In acquired amusia, inability to perceive music correlates with an inability to perform other higher-level functions. As musical ability improves, so too do the higher cognitive functions which suggests that musical ability is closely related to these higher-level functions, such as memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
and learning
Learning
Learning is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information. The ability to learn is possessed by humans, animals and some machines. Progress over time tends to follow learning curves.Human learning...
, mental flexibility, and semantic fluency.
Amusia can also be related to aprosody
Aprosody
Aprosody refers to the lack of variations in normal speech characteristics, such as speed, tone, and varied emphasis. It is mentioned in the context of medical diagnosis, similar to ataxia and aphasia....
, a disorder in which the sufferer's speech is affected, becoming extremely monotonous. It has been found that both amusia and aprosody can arise from seizures occurring in the non-dominant hemisphere. They can also both arise from lesions to the brain, as can Broca's aphasia come about simultaneously with amusia from injury. There is a relation between musical abilities and the components of speech, however, they are not understood very well.
Social and emotional impact
Other than their inability to hear music, which is most likely due to a genetic defectGenetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....
, the rest of an amusic's brain remains normal. The only effect is on the ability to tell different notes apart due to the separation of two key areas in the brain. Most sufferers of amusia describe music as unpleasant. Others simply refer to it as noise and find it annoying. This can have social implications because amusics often try to avoid music, which in many social situations is not an option. In China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
and other countries in which identical words have different meanings based on pitch, amusia may have a much more pronounced social and emotional impact; difficulty in speaking and understanding the language.
Treatment
Currently, no forms of treatment have proven effective in treating amusia. One study has shown tone differentiation techniques to have some success, however future research on treatment of this disorder will be necessary to verify this technique as an appropriate treatment.Future research
Over the past decade, much has been discovered about amusia. However, there remains a great deal more to learn. While a method of treatment for people with amusia has not been defined, tone differentiation techniques have been used on amusic patients with some success. It was found with this research that children reacted positively to these tone differentiation techniques, while adults found the training annoying. However, further research in this direction would aid in determining if this would be a viable treatment option for people with amusia. Additional research can also serve to indicate which processing component in the brain is essential for normal music development. Also, it would be extremely beneficial to investigate musical learning in relation to amusia since this could provide valuable insights into other forms of learning disabilities such as dysphasia and dyslexiaDyslexia
Dyslexia is a very broad term defining a learning disability that impairs a person's fluency or comprehension accuracy in being able to read, and which can manifest itself as a difficulty with phonological awareness, phonological decoding, orthographic coding, auditory short-term memory, or rapid...
.
Famous sufferers
- Theodore RooseveltTheodore RooseveltTheodore "Teddy" Roosevelt was the 26th President of the United States . He is noted for his exuberant personality, range of interests and achievements, and his leadership of the Progressive Movement, as well as his "cowboy" persona and robust masculinity...
- Che GuevaraChe GuevaraErnesto "Che" Guevara , commonly known as el Che or simply Che, was an Argentine Marxist revolutionary, physician, author, intellectual, guerrilla leader, diplomat and military theorist...
- Milton FriedmanMilton FriedmanMilton Friedman was an American economist, statistician, academic, and author who taught at the University of Chicago for more than three decades...
- Sigmund FreudSigmund FreudSigmund Freud , born Sigismund Schlomo Freud , was an Austrian neurologist who founded the discipline of psychoanalysis...
- Ulysses S. GrantUlysses S. GrantUlysses S. Grant was the 18th President of the United States as well as military commander during the Civil War and post-war Reconstruction periods. Under Grant's command, the Union Army defeated the Confederate military and ended the Confederate States of America...
- Charles DarwinCharles DarwinCharles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...