Absolute pitch (AP) is the ability to identify the pitch of a musical tone or to produce a musical tone at a given pitch without the use of an external reference pitch 
. The estimated prevalence of AP is frequently reported to be around 1 per 10,000 
, although a higher prevalence has been reported among East Asian populations 
. AP possessors are able to retain accurate information about an isolated pitch along the one-dimensional continuum of auditory frequency, and they are able to label that pitch within the context of the western chromatic scale 
. It has been argued that the development of AP depends on musical exposure in a critical period in early childhood 
as well as on possible genetic contributions 
. However, many musicians who begin training early in life and come from musical families do not develop AP, and relatively little is known about the traits and personality features associated with AP ability.
It has been suggested that AP ability may be associated to some extent with certain deficits, since there seems to be an increase in prevalence of AP among people with sensory and developmental disabilities. For example, AP is frequently reported in individuals with congenital blindness 
, Williams syndrome 
, and autism spectrum disorder (ASD) 
. In one study, Heaton et al. 
investigated AP in an intellectually-able adult with autism who had not experienced early musical training and observed statistically superior pitch naming in comparison with musically-trained typically-developing controls with AP. These results suggest that the genesis of AP may be different in ASD, and that pitch information is encoded with increased specificity in these individuals.
In the current version of the Diagnostic Statistical Manual (DSM-IV-TR) 
, autism is one of a cluster of disorders that are characterized by impaired social and communicative skills and co-occurring repetitive behaviors. Asperger syndrome is a subcategory that is characterized by the same core deficits as autism, but unlike autism, is not associated with delays in attaining early language and cognitive milestones. However, research suggests that at later developmental stages, individuals diagnosed with Asperger syndrome may show comparable levels of symptom severity as those who had experienced language and cognitive delays but were intellectually able (high-functioning autism) 
In recognition of this and other failures to reliably differentiate between the different sub-categories detailed in DSM-IV-TR, it is proposed that the upcoming revision of the manual (DSM-V) will include a single spectrum disorder (ASD).
A notable feature of ASD is that unusual skills, as noted in the study by Heaton et al. 
appear to be fairly common. Theoretical accounts of autism, for example, the Enhanced Perceptual Functioning theory 
, propose that individuals with ASD show superior perceptual discrimination and, in addition, display an analytical cognitive style with increased pattern discrimination abilities. Interestingly, Chin’s 
two-factor model of AP describes a genetic predisposition toward an “analytical cognitive style”, and this may account for increased levels of AP in autism.
Although ASD is considered to be a clearly defined neurodevelopmental disorder there is an increasing recognition that some of its defining characteristics can be observed at sub-clinical levels in the general population. Baron-Cohen et al. 
have developed the Autism-spectrum Quotient (AQ) questionnaire to measure social skills, communication, imagination, attention to detail and attention switching in typical populations. The AQ questionnaire includes 50 items (i.e. personal statements) and participants are required to indicate whether or not the statements apply to them. For example, the statement “I enjoy social chit-chat
” is included in the communication subscale question set, and “I prefer to do things the same way over and over again
” is included in the attention switching subscale. The score ranges from 0 to 50, with higher scores indicating a higher prevalence of autistic traits. Baron-Cohen suggests that individuals who score above 32 points should be considered to have clinically significant levels of autistic traits 
. Three of the five different AQ subscales measure what has come to be known as the “triad” of impairments characterizing autism. Hence, these questions probe social and communication skills and a tendency to repetitive behavior. The remaining subscales probe for characteristics of autism that have been identified in experimental studies. These include difficulties in imagination, difficulties in attention-switching, and exceptional attention to detail. Difficulties in attention switching are associated with poor cognitive flexibility and are consistent with work showing impaired executive functions in ASD 
. Exceptional attention has been associated with special skills and may be associated with an analytical cognitive style detailed in the models of autism outlined by Mottron 
and Baron-Cohen 
. Interestingly, given questions about the prevalence of AP in autism, an analytical cognitive style is an important component in the model of AP proposed by Chin 
Studies using the AQ with typical adults have shown that natural science students have higher AQ than students from the social sciences and humanities, and that mathematicians have higher AQ than non-mathematician scientists 
. These findings are consistent with previous studies showing an association between science/maths skills and autistic conditions 
using other methods. Other studies using the AQ have shown that high AQ scorers are faster to complete the Embedded Figures (EF) test compared with low AQ scorers, independent of global IQ scores 
. The EF task requires individuals to locate a simple form that is embedded in a larger visual display. It provides a measure of the individual’s field independence, defined as the ability to isolate details from their surrounding context. An early study by Shah and Frith 
revealed superior EF task performance in children with autism, and these more recent findings, showing similarly superior performance in typical individuals with high AQ suggest similarities in cognitive style across these two groups. However, there is some evidence that abnormalities in perceptual processing are characteristics of individuals with high AQ scores. In a study by Gomot et al. 
it has been observed that individuals with high AQ scores demonstrate superior auditory novelty detection, revealed by shorter reaction time, in a task requiring response to target stimuli in an oddball paradigm. They also displayed activation of an unusually widespread network of brain regions that are also observed in individuals with a formal diagnosis of autism 
Recently, a preliminary interview-based study carried out by Brown et al. 
examined individual differences associated with the presence of AP in groups of classical trained musicians. The subjects were classified as being definitely socially eccentric, somewhat eccentric, or not eccentric on the basis of interviewer’s notes regarding subjects’ communication style and nonverbal behavior. The results showed that individuals classified as “socially eccentric” were more likely to be AP possessors. Whilst these findings are intriguing, it must be noted that the data were largely qualitative in terms of being interview-based and the groups were not matched for age, age of onset of musical training, or musical preference.
In the present study, we aimed to determine whether or not musicians with AP show increased levels of autism traits compared to matched groups of musicians without AP and non-musicians. Accordingly, we measured the autism traits of the participants quantitatively by administering the AQ and the level of AP ability using a pitch identification test, on the hypothesis of a correlation between the two. Finding higher scores on the AQ subscales measuring social and communication deficits in our AP group would be consistent with the results of Brown et al. 
, whereas differences on the subscales measuring attention-switching and attention to detail would support the model by Chin 
who claim that AP is associated with detailed processing style. Finally, we examined whether musical abilities vary with degrees of autism traits and whether the level of AP ability is reliably related to musical aptitude.