The simultaneous processing of motor and cognitive demands is necessary for the production of written text. Children develop automaticity in their handwriting while learning to write, such that motor demands of writing doesn’t interfere with higher-order cognitive processes related to composition. When this automaticity isn’t present, the flow and planning of ideas and their translation into written form may be disrupted, which affects the complexity of the text.

Furthermore, the quality of handwriting is significantly correlated with the level of academic achievement during school years, and is a predictor of more general learning difficulties later in life. The World Health Organization (WHO) therefore identifies the skill of writing as part of the Activities and Participation Domain of health. Poor handwriting can also affect the perception of a child’s abilities, self-esteem, personal relationships and psychosocial well-being.

Children with neurodevelopment disorders such as ADHD, DCD and ASD often experience handwriting difficulties. Autism Spectrum Disorder concerns neurodevelopmental disorders characterized by symptoms such as presence of restrictive, repetitive and stereotypical behaviors, activities and interests plus impairments in communication and social interaction. ASD is also often associated with fine motor difficulties and executive function impairments which are necessary for the performance of skilled motor task. This explains why ASD in children is often related with handwriting difficulties.

Determinants of handwriting function

Learning and acquisition of handwriting is a function of the interaction between the child, the writing task and the environment. The Sequential Handwriting Process argues that the handwriting process starts with the presentation of the text to be written. This can be a visual, audial or self-intended presentation. Second, a series of cognitive steps have to be taken to retrieve the motor program for the appropriate letter allograph. This translates into specific control instructions for muscle groups concerning the size and speed of the required movement. Appropriate force on the pen and paper, movements within strict spatial limits and the use of the correct velocity are all necessary factors for fluid handwriting. Sensory perceptual feedback provides information for error correction.

Fine motor skills enable fluent manipulation of the writing and thereby producing letters with the desired specific form, size and position on the writing surface. The quality of handwriting therefor logically correlates with aspects of fine motor control. Deficits to the fine motor skills often occur in children with ASD, especially in children with Asperger’s syndrome. Proper timing and force control of the arm, hand and finger movements derive from fine motor skills, and are all necessary to produce accurately formed letters. Children with ASD also regularly experience difficulties with planning, executing and organizing movements or suffer from dyspraxia which both affect coordination, fluency and speed of motor activities. Since movement planning is necessary to produce handwriting, these impairments also cause problems producing written text. They therefore develop a certain slowness in their movement preparation and reaction times. Muscle tone, muscle stress and tension and pencil grip are also important factors in producing handwriting but are often impaired in individuals suffering from ASD.

Another integral part of proficient handwriting, specifically in the planning and execution of the written product, are visual perception skills. Not only do those skills allows to discriminate between letter forms, they also provide information for error monitoring. Interestingly, since handwriting movements are highly pre-structured and organized, the reliance on vision generally diminishes as skilled handwriting develops. ASD is particularly associated with atypical patterns in visual processing, including differences in perception of motion, superior processing of fine details and atypical processing of global structure. Overall, ASD is not associated with global deficits in visual reasoning and discrimination, but the atypical patterns of visual perception in ASD might contribute to handwriting difficulties.

Visual-motor integration is the ability to integrate the visual images of letters or shapes with the appropriate motor response. This is typically assessed by examining the ability of children to copy geometric forms using pencil and paper. It is therefore considered as a degree of coordination between visual perception and hand-finger movements. The ability of visual-motor integration significantly correlates with the production of legible handwriting. So far, no strong evidence has been found that children with ADHD exhibit deficits in visual-motor integration. Sins visual-motor integration combines both motor abilities and visual perception, poor performances may result from impairments in one of these two domains or in the integration of the two domains.

The awareness of the movement and position of limbs in space as well as information regarding touch, pressure and pain are referred to as kinesthesia and proprioception. Kinesthesia provides feedback and a monitoring of extent and force or speed of movements for the purpose of error correction. The ability to improve performances over time could be hindered by deficits in kinesthetic perception. Currently there is no significant evidence suggesting deficits in kinesthesia and proprioception in children with ASD.

Studies on handwriting in individuals with ASD

Officially, the quality of handwriting is measured in terms of speed and legibility. Legibility refers to the recognizability of handwriting and includes factors such as sizing, alignment, letter form and spacing. Several studies have reported poor legibility in children with ASD, especially in the area of letter formation. The quality of letters is measured by letter form which considers factors such as shape reversals, distortions and rotations. Commonly found mistakes in the handwriting of children with ASD are sharp edges instead of smooth curves and larger letter extensions. Poor letter formation may be due to difficulties with fine motor skills and pencil manipulation.

Several researches show a lot of discordance with regard to alignment, spacing and sizing. Although deficits in all of these areas are expected considering the impairments in visual perception and visual motor integration, only one study has shown poorer performances than peers without ASD. The same accounts for speed. Interestingly though, increased consistency in letter formation was reported to be associated with a decrease in speed in children with ASD but not in typically developing peers.

Very few research has been conducted on the nature of handwriting difficulties in children with ASD. The most consistent finding is that legibility, especially letter formation, is impaired in children with ASD. This impairment positively correlates with deficits in motor skills. The great amount of disparity in several researches may be due to differences in the nature of the writing tasks used in the studies and the heterogeneity of the ability profiles in children with ASD. Also, the current studies have mainly focused on the final, static written product while writing is a dynamic process involving changes in direction, forces, velocities and accelerations. So far no research has been conducted on these process-related aspects.