Postural Stability and Its Limits in Autism Spectrum Disorder Relate to Visual Context

Background:  

Many studies of ASD report behavioral and neural differences in visual and motor systems. However, few studies of Autism Spectrum Disorder (ASD) quantitatively examine visuomotor integration – the use of visual information to guide motor behavior – and its influence on postural stability. Postural stability is a critical building block of motor development with downstream influence on a wide array of functional skills (e.g., ambulation, gesturing, self-care, driving, playing physical games). 

Objectives:  

To define the relationship between postural stability, eye movement, and visual context in ASD.

Methods:  

We conducted a preliminary investigation of visuomotor integration in 3 adolescent participants with ASD and 3 age-matched typically-developing (TD) controls. Data were collected in a community setting using mobile eye-tracking and a portable force platform. Participants completed the Clinical Test of Sensory Integration in Balance (CTSIB), which requires quiet standing with eyes open, with eyes closed, and with eyes open while wearing a translucent dome over the head. The dome condition tests stability when visual and proprioceptive systems are stimulated, but context-based visual information is unavailable. Participants also completed 3 runs of a Limits of Stability task, which requires participants to shift Center of Pressure (CoP) to reach each of 9 target positions displayed on a screen. 

Results:  

The ASD group had higher sway and stability indices than the TD group across all 3 conditions of the CTSIB (eyes open, eyes closed, dome) (Fig. 1). The ASD group also had greater increases in sway and stability indices between conditions of the CTSIB as difficulty increased. Standard deviations were considerably larger in the ASD across all variables. The ASD group had lower control than the TD group for 5 of the 9 Limits of Stability target positions (2, 3, 4, 6, 7), but higher control than participants in the TD group for 4 positions (1, 5, 8, 9), two of which required only lateral movement (1, 5) and one of which was the center position (9). Overall, the ASD group had lower average control than the TD group across all targets, and took longer to complete the test. Time to complete is a proxy for movement accuracy, since the task advances when participants meet hit criteria for each target. Again, standard deviations were considerably larger in the ASD group for most variables. 

Conclusions:  

Results from postural stability data support our hypothesis that individuals with ASD would have greater postural instability than TD controls. When visual context was eliminated (CTSIB dome condition), individuals with ASD had markedly greater impairment in stability, suggesting that integration of context-based visual information into motor plans may have greater influence than visual or proprioceptive information alone. Further, when limits of stability were tested, individuals with ASD had greater difficulty maintaining postural control during a CoP shift, especially for more difficult target positions. Preliminary examination of eye movement data also suggests that atypical gaze patterns relate to impairments in postural stability, and postural stability is significantly impacted by the presence or absence of visual context (i.e., CTSIB condition) in ASD.