Handedness in autism spectrum disorders and intellectually disabled children and adolescents – Contrasting caregivers’ reports with assessments of hand Preference



Handedness, or the preference for using one hand over the other, is a fascinating aspect of human behavior. It is influenced by both genetic and environmental factors, and it is related to brain structure and function. Most people are right-handed, but some are left-handed or mixed-handed (using different hands for different tasks).


Handedness is also relevant for studying developmental disorders, such as autism spectrum disorder (ASD) and intellectual disability (ID). Previous research has suggested that people with ASD have a higher rate of atypical handedness (non-right-handedness) than people with other types of developmental disorders or typically developing people. However, the exact difference and the possible reasons for it are not well understood.


A recent study aimed to address this gap by comparing the handedness of individuals with ASD and ID in two countries: Iran and the Kurdistan Region of Iraq (KRI). The study also examined how the caregivers of these individuals perceived their handedness and how it matched with the results of a standardized hand preference test.


How was the study done?


The study involved 1116 individuals with developmental disabilities, 541 from Iran and 575 from KRI. The participants were divided into four groups based on their diagnosis: ASD, ID, ASD+ID (both ASD and ID), and other (such as cerebral palsy, Down syndrome, etc.). The participants ranged in age from 3 to 25 years, and most of them were male (82.5%).


The handedness of the participants was assessed in two ways: by asking their caregivers to report their hand preference for various activities, and by using a hand preference demonstration test (HPDT). The HPDT is a simple and quick test that involves asking the participants to perform 10 tasks with their hands, such as pointing, clapping, throwing, etc. The test is scored based on the number of times each hand is used, and the results are classified into four categories: right-handed, left-handed, mixed-handed, and no preference.


What were the main findings?


The study found that there was a significant difference between the caregivers’ reports and the HPDT results for the participants’ handedness. The caregivers tended to overestimate the right-handedness and underestimate the atypical handedness of their dependents. For example, 82.8% of the caregivers reported that their dependents were right-handed, while only 54.6% of them were classified as right-handed by the HPDT.


The study also found that the participants with ASD had a higher rate of atypical handedness than the participants with ID or other disorders. The prevalence of non-right-handedness, left-handedness, and mixed-handedness was 45.4%, 18.3%, and 36.1%, respectively, among the participants with ASD, compared to 28.9%, 11.2%, and 17.7%, respectively, among the participants with ID. These findings are consistent with previous studies that have reported a higher rate of atypical handedness in ASD.


The study also explored some possible factors that could influence the handedness of the participants, such as age, gender, country, and diagnosis. The study found that younger participants, male participants, and participants from KRI were more likely to be atypical in their handedness. The study also found that the participants with ASD+ID had the highest rate of atypical handedness, followed by the participants with ASD, ID, and other disorders.


What are the implications of the study?


The study has several implications for understanding and supporting individuals with developmental disabilities, especially those with ASD. The study highlights the importance of using a valid and reliable measure of handedness, such as the HPDT, rather than relying on the caregivers’ reports, which may be biased or inaccurate. The study also suggests that handedness may be a useful marker for identifying and diagnosing ASD, as well as for studying the brain structure and function of individuals with ASD.


The study also raises some questions for future research, such as why there is a higher rate of atypical handedness in ASD, and what are the consequences of it for the cognitive and social development of individuals with ASD. The study also calls for more cross-cultural and longitudinal studies on handedness in developmental disorders, as well as more interventions to promote the optimal use of both hands in individuals with atypical handedness.



What is the difference between handedness and hand preference?


Handedness is the general tendency to use one hand more than the other for various tasks, while hand preference is the specific choice of hand for a particular task. For example, a person may be right-handed in general, but prefer to use their left hand for writing or eating.


How is handedness related to brain structure and function?


Handedness is associated with the lateralization of brain functions, or the distribution of cognitive abilities across the two hemispheres of the brain. The left hemisphere is typically dominant for language and analytical skills, while the right hemisphere is more involved in spatial and creative tasks. Right-handed people tend to have a stronger left hemisphere dominance, while left-handed and mixed-handed people may have a more balanced or reversed brain lateralization.


How can caregivers support individuals with atypical handedness in ASD?


Caregivers can support individuals with atypical handedness in ASD by respecting their hand preference and encouraging them to use both hands for different tasks. Caregivers should avoid forcing or correcting the hand preference of individuals with ASD, as this may cause frustration, anxiety, or low self-esteem. Caregivers should also provide opportunities for individuals with ASD to practice and improve their hand skills, such as fine motor, coordination, and dexterity, through various activities, such as drawing, playing, or writing. Caregivers should also monitor the academic and social performance of individuals with ASD and seek professional help if needed.


How can educators support individuals with atypical handedness in ASD?


Educators can support individuals with atypical handedness in ASD by providing a flexible and inclusive learning environment that accommodates their hand preference and learning style. Educators should avoid imposing or penalizing the hand preference of individuals with ASD, as this may affect their motivation, confidence, or achievement. Educators should also provide appropriate tools and materials that suit the hand preference of individuals with ASD, such as scissors, pencils, or keyboards. Educators should also differentiate the instruction and assessment methods to meet the diverse needs and abilities of individuals with ASD.




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