Introduction
Autism is a developmental condition that affects how people communicate and interact with others. It also affects how they control their movements. Many autistic individuals show motor atypicalities, such as difficulties with fine motor skills, coordination, and timing. These motor differences may relate to the social challenges that autistic people face.
One way to measure motor control is to look at how people follow the two-thirds power law (2/3 PL). This is a mathematical rule that describes how the speed and curvature of human movements are related. For example, when you draw a circle, you tend to slow down when you make a sharp turn and speed up when you move along a straight line. This makes your movement smooth and efficient. The 2/3 PL captures this pattern and applies to many forms of human movement, such as writing, drawing, walking, and reaching.
A new study investigated how autistic children adhere to the 2/3 PL compared to typically developing (TD) children. They used a smart tablet activity to record the finger movements of children aged 4–8 years old as they drew and traced ellipses on an iPad. They then computed how well the children followed the 2/3 PL and other kinematic metrics, such as velocity, acceleration, and jerk. They also collected measures of cognitive and motor functioning from the children.
Results
The study found that autistic children showed less adherence to the 2/3 PL than TD children. This means that they modulated their speed more between curved and straight sections of movement, resulting in less smooth and more variable movements. They also showed higher levels of acceleration and jerk, indicating more abrupt changes in speed and direction. Moreover, they showed more intra- and inter-individual variability across several kinematic variables, suggesting less consistency and stability in their motor control.
The study also found that TD children showed significant motor control development with age, but autistic children did not. This implies that autistic children may have a developmental delay or stasis in their motor control. Furthermore, the study found that motor control adherence to the 2/3 PL was related to cognitive and motor functioning in both groups, but more strongly in the autistic group. This suggests that motor control may be a more sensitive indicator of autism than other measures.
Implications
This study is the first to examine motor control adherence to the 2/3 PL in autistic children, revealing overall diminished motor control. The authors suggest that this may reflect a disruption in the sensorimotor integration that underlies human movement. They also propose that motor control may be a useful biomarker for autism, as it can be easily and objectively assessed using smart tablet technology.
The study has important implications for understanding the autism motor signature and its relation to social communication. It also opens up new avenues for developing interventions that target motor control in autistic children, such as tablet-based games, exercises, or therapies. By improving motor control, autistic children may also enhance their social skills and well-being.
FAQ
What is the two-thirds power law (2/3 PL) and why is it important for motor control?
The 2/3 PL is a mathematical rule that describes how the speed and curvature of human movements are related. It states that the speed of a movement is proportional to the radius of curvature raised to the power of -1/3. This means that when people move along a curved path, they tend to slow down when the curvature is high and speed up when the curvature is low. This makes the movement smooth and efficient. The 2/3 PL is important for motor control because it reflects the optimal way of coordinating the muscles and joints to produce a desired movement.
What are the possible causes of the reduced adherence to the 2/3 PL in autistic children?
The researchers suggest that the reduced adherence to the 2/3 PL in autistic children may reflect a disruption in the sensorimotor integration that underlies human movement. Sensorimotor integration is the process of combining sensory information (such as vision, touch, and proprioception) with motor commands (such as muscle activation and joint angles) to produce a coordinated movement. Autistic children may have difficulties in processing and integrating sensory information, which may affect their ability to adjust their movements according to the 2/3 PL.
What is the smart tablet activity that the researchers used to record the finger movements of the children?
The smart tablet activity was a custom-made app that ran on an iPad. The app presented the children with a series of ellipses of different sizes and orientations on the screen. The children were instructed to either draw or trace the ellipses using their index finger. The app recorded the x- and y-coordinates, time stamps, and pressure of the finger movements, as well as the ellipse parameters.
Why did the researchers choose ellipses as the stimuli for the smart tablet activity?
The researchers chose ellipses as the stimuli for the smart tablet activity because they are simple geometric shapes that can vary in size and orientation, and because they have a well-defined curvature profile that can be used to test the adherence to the 2/3 PL. Ellipses also allow for the comparison of drawing and tracing tasks, which involve different levels of motor planning and execution.
How can parents and caregivers help autistic children improve their motor control and adherence to the 2/3 PL?
Parents and caregivers can help autistic children improve their motor control and adherence to the 2/3 PL by providing them with opportunities and feedback for motor learning and practice. For example, they can encourage them to engage in physical activities that involve drawing, tracing, or following curved paths, such as painting, coloring, or playing with puzzles. They can also use smart tablet technology to monitor and measure their motor performance and provide them with visual and auditory feedback. Additionally, they can support them in social and interactive activities that involve movement coordination, such as dancing, playing catch, or mimicking gestures.
Source:
https://link.springer.com/content/pdf/10.1007/s10803-024-06240-6.pdf