Increased Centre-of-Pressure Regularity during Quiet Stance in Adults with Autism Spectrum Disorder

Background: Adults with autism spectrum disorders (ASD) demonstrate atypical postural sway however the underlying processes that cause this are unclear. One hypothesis is that people with ASD rely less on vision and more on somatosensory input when controlling posture. Less use of vision for postural control may put people with ASD at disadvantage in developing complex motor skills and adaptive behaviours. The movement of the centre of pressure (COP) during postural control represents the accumulation of control processes and responses to maintain an upright posture. In general, the mediolateral postural control depends more on visual information whereas the anteroposterior postural control depends more on somatosensory information. Entropy measures the regularity or amount of information in a signal. A larger magnitude of entropy indicates more irregular COP fluctuations and higher automaticity of postural control.

Objectives:  The primary aim of this study was to compare the regularity of the COP fluctuations in adults with ASD to their typically developed peers, with and without vision.

Methods:  The study used a quasi-experimental case control design with nineteen adults with ASD and twenty-nine typically developed adults. COP position was collected at 100 Hz in two directional dimensions (mediolateral and anteroposterior) during quiet stance on a force platform in visual conditions of eyes open and eye closed. Each condition lasted for 30 seconds. Sample entropy and the Romberg quotient were calculated.

Results: Group differences in entropy were only evident in the eyes open condition in the anteroposterior direction (p=0.038). Mean entropy was smaller in the ASD group by 0.029 (95% CI -0.056 to -0.002). No difference was observed in entropy between the groups in the eyes open condition in the mediolateral direction (p=0.337), and the in the eyes closed condition in either direction (mediolateral p=0.716 and anteroposterior p=0.904, respectively). Additionally, the Romberg quotient of adults with ASD was significantly lower than that of typically developed adults (p=0.032). The Romberg quotient in the ASD group was lesser by 0.217 (95% CI -0.415 to -0.194), indicating a smaller contribution of vision on standing postural control in adults with ASD than typically developed adults.

Conclusions: In the anteroposterior direction, adults with ASD had a smaller magnitude of entropy demonstrating COP fluctuations that were more regular compared with those of TD. Regular COP fluctuations suggest a less adaptable and more attention demanding control of posture. It also indicates a lesser automatic postural control in the anteroposterior for adults with ASD. Cognitive load, disease state, old age, restricted vision and concussion have all been reported to be associated with more regular COP fluctuations. In combination with the smaller contribution of vision on postural control in adults with ASD, the findings are consistent with the previously reported hypothesis that postural control in ASD is biased to somatosensory information. The findings of this study have implication on guiding the development of intervention in areas of motor skills for people with ASD.