|Absolute Pitch has been frequently reported in people with autism.|
It has been frequently reported in people with sensory and developmental disabilities, including Autism Spectrum Disorder (ASD), Williams syndrome, and congenital blindness, that they possess absolute pitch (AP), the ability to identify the absolute frequency of a pitch without any external sources of reference. AP has been found to be prevalent especially among those with ASD, with the likelihood as high as 5%. Researchers have tried to look for the correlations between AP and ASD by investigating the neuroanatomical and cognitive aspects. One of the key topics has been the atypical asymmetry of planum temporale (PT) that might be behind the link between AP possessors and developmental disabilities, but more work on the underlying correlations needs to be done in the future.
Table of Contents
1) Absolute Pitch Overview
AP is a rare ability, only found in 1 out of 10 000 people in Western countries, while those in Asian countries were interestingly more likely to be found to possess AP, due to the fact that Asian languages are used with great emphasis in tone and many children start music in early life. Even among musicians, the incidence rate is known to be less than 20%.
The absolute underlying factors behind the onset of AP are not clear, but it is known as of now to be manifested at an early age, 3 to 6, mostly through musical training. Many scientists have looked for the reasons behind this special pitch recognition ability and found and wondered what ASD has got to do with everything.
2) AP & ASD: Correlations
Deficits in the cognitive flexibility and executive functions have been commonly thought to explain the underlying behaviours and symptoms of autistic patients.
2.1) Similarities in Cognitive, Social Characteristics
Frith in 1989 introduced the concept of "weak central coherence," the typical trait found in autistic people. It is a term describing the tendency for autistic people to focus on details and local features instead of looking at the whole context. Since then, AP as it is an ability to recognize single notes, rather than the whole music, was studied closely together with ASD as they seemed to have similar cognitive and social characteristics underlying both.
In a case study with an autistic girl, QC, she was found to display exceptional AP abilities, but she suffered deficit in her executive functions, such as cognitive flexibility, which explained the repetitive behaviours seen in autistics . The authors hypothesized that her impairment in cognitive flexibility seemed to be the most applicable and valid cognitive deficit that led to her exquisite pitch processing abilities. Both the "Central Coherence" by Frith and "Executive Deficit" by Turner hinted at the underlying factor that allow an individual to possess special abilities along with autism and cognitive deficits. This underlying factor may be the early onset of musical training, triggering one's genetic factors during a child's critical developmental period. Overall, the artists concludes by suggesting AP does not arise from deficits in one's processing of the whole or global information, but possibly due to the insufficient cognitive flexibility that is associated with one's early developmental predisposition for interest in music.
3) Asymmetry in Planum Temporale
Planum temporale (PT) is a region in the temporal lobe  in the brain, known to be associated with language as well as auditory processing . Generally in right-handed individuals, PT is observed to be asymmetrical with its left hemisphere bigger in size than its right. Over the years, PT has been useful in determining hemispheric dominance in clinical research. More importantly, alterations in the PT asymmetry have been hypothesized to underlie many clinical subjects, such as schizophrenics and dyslexics.
3.1) AP Possessors’ PT
|PT size asymmetry in AP musicians|
|Greater PT asymmetry was observed in one of the AP musicians (AP-Mus), with
significantly reduced size of the right hemisphere, compared to the non-musicians (N-Mus) group.
In 1995, PT asymmetry and AP have been suspected to be correlated due to larger size difference between the left and right hemisphere of PT – greater leftward asymmetry – observed in AP musicians compared to non-AP musicians. In 1998, the suspected difference in PT asymmetry was observed in AP musicians compared to a large control group. However, consistent results could not be seen with smaller sample group. The underlying factor behind the increased left hemisphere asymmetry in AP musicians is not clear, but scientists suspect that early experience with music may have an influence in the amount of difference in size of both hemispheres.
Keenan et al. in 2001, looked to see which hemispheres – left or right – account for the increased asymmetry in AP musicians by measuring volumes of PT regions and taking magnetic resonance imagings. They first found that there was greater leftward asymmetry in PT size for AP musicians compared to control groups. They also found that the right hemisphere of the AP musicians group was significantly smaller in size, with which they analyzed that it is actually the right, not left hemisphere that would better indicate AP possessors in musicians. The reasons behind greater left and smaller right hemisphere in AP musicians may be due to early music experiences, but genetic factors also have to be taken into account, because in the same study, same observations were not seen in non-AP musicians with early exposure to music.
3.2) ASD Patients’ PT
|PT size asymmetry in ASD patients|
|Lack of PT asymmetry exists in the children in autism group compared to the healthy children.|
Knowing ASD patients suffer from communication deficits and the function of the PT in language, great interest has been shown in PT asymmetry. In a study with autistic adults by Rojas et al., PT’s grey matter volume of the left hemisphere was observed to be reduced compared to the control group, with the right hemisphere volume relatively unchanged. They concluded that the results supported their hypothesis of the difference in the PT asymmetry volumes in autistic patients – the lack of asymmetry in volumes. This study, however, did not take account for autistic children and adolescents, and there were not enough test subjects that fit into all categories of ASD to extrapolate the results to all ASD patients.
In 2005, they decided to look at the PT volumes of autistic children and adolescents with MRI scans compared to the control group . Similar to the study with autistic adults, grey matter volumes in PT and Heschl's gyrus (HG) were measured. They observed that PT volume of left hemisphere was greater than the right in the control group, as was expected. In the autistic group, smaller volume of the left hemisphere was found, just as the data from 2002 study with the adult patients showed, which supported their hypothesis that there indeed is a lack of asymmetry in PT. Together with the data from both studies, the authors suggested that the left hemisphere may be responsible for the changes made to the language and auditory-related brain regions for autistic patients. Just as Keenan et al. stated, they concluded by saying the lack of increased left hemisphere may be also due to the early musical exposure, and may even manifest in early development, but more research needs to be conducted.
4) AP Possessors & Autistic Traits
4.1) Musicians with AP & Autistic Traits
|AQ test scores|
|AP musicians scored significantly higher in the AQ test than the other two control groups.|
In 2012, Dohn et al. looked for the relationship between AP and autism traits, by measuring the levels of autism using the "Autism Spectrum Quotient" (AQ) for three test groups: AP musicians, non-AP musicians and non-musicians . AQ is a questionnaire developed by Baron-Cohen et al. that measures individual’s autistic traits such as social, communication skills, attention and other typical ones seen in ASD patients. Out of 50 points, having scored 32 or more is thought to possess high levels of autism traits. The AP musicians were first tested for AP through the pitch identification test (PIT); the musical ear test (MET) was written for all participants. Lastly, AQ was completed by all participants.
The authors concluded that AP was more prevalent among musicians compared to non-musicians then found that those musicians with AP scored significantly higher on the AQ than the other experimental groups. They concluded that there was a positive correlation between the scores for both the PIT and MET and thus, between possessing AP and developing autism traits.
This study was the first to start looking at the non-autistics AP possessors and the possibilities of developing different traits related to ASD. However, it is important to note that AP musicians did score high with regards to aspects on the AQ test, such as imagination and attention-related items, rather than social and communication skills, the core traits seen in ASD patients. Nevertheless, the idea that people who are predisposed to developing AP are also prone to have more autism traits is very fascinating and may provoke new research in the near future.
5) AP and other Sensory & Developmental Disabilities
Next to ASD, other sensory and developmental disabilities, such as Williams syndrome and congenital blindness have been a great interest for many researchers for the possible correlations that may exist between AP possession and the clinical disabilities. It has been noted that those with ASD and other disabilities have extraordinary talent for musical abilities, just like Derek Paravacini, a blind man with ASD.
|Musical genius: Derek Paravacini|
5.1) AP & Williams Syndrome
Lenhoff et al. in 2001 looked at whether individuals with Williams syndrome can acquire AP. For experimental participants, they recruited five with some musical knowledge, who could read or name musical notes. After confirming they all had Williams syndrome, they underwent number of tests to check for possession of AP ability. They found that all five individuals with did possess AP, despite their deficits in cognitive abilities.
From this experiment, 1 out of 20 000 of those with Williams syndrome could be extrapolated to possess AP, but only 4500 existed in Canada and US at the time of this study. Future work needs to be done with more people with Williams syndrome to calculate the incidence rate.
5.2) AP & Congenital Blindness
Hamilton et al. in 2004 experimented with 46 blind subjects and found 12 of them possessed AP, 57.1%, an amazing prevalence compared to the general population . Another important finding was that out of those blindness subjects, the average age, 8 years, for them to have started musical training was far higher compared to the general population also. MRI from blind musicians with AP was also used to prove difference in PT hemisphere asymmetry exists: larger amount of difference in size was seen compared to the non-AP musician and non-musician groups. All in all, the authors hypothesized that AP in blind musicians work differently in two ways: early musical training is not a prerequisite as it is for the general population and the increased PT asymmetry is a factor underlying their higher prevalence of AP possession. Replicating the same findings in larger populations of blind musicians would be the future goals for scientists to find out the absolute criteria.