Motor atypicalities in infancy are associated with general developmental level at 2 years, but not autistic symptoms

Abstract

Atypicalities in motor functioning are often observed in later born infant siblings of children with autism spectrum disorder. The goal of our study was to investigate motor functioning in infants with and without familial history of autism spectrum disorder. Specifically, we investigated how infants catch a ball that is rolling toward them following a non-straight path, a task that requires both efficient planning and execution. Their performance was measured using detailed three-dimensional motion capture technology. We found that several early motor functioning measures were different in infants with an older autistic sibling compared to controls. However, these early motor measures were not related to autistic symptoms at the age of 2 years. Instead, we found that some of the early motor measures were related to their subsequent non-social, general development. The findings of our study help us understand motor functioning early in life and how motor functioning is related to other aspects of development.

Keywords: autism spectrum disorder; infancy; interceptive action skills; motion capture technology; motor development.

Figure 1.

Sketch of the experimental setup with infant and test leader sitting opposite of each other at a quadratic table with adjustable tabletop.

Figure 2.

Example velocity profile from one of the participating infants. A reach is divided into movement units (MUs) from their local minima. The transport unit (TU) represents the largest MU toward the target. The main kinematic variables were the TU peak velocity (as shown by arrow) and TU distance traveled (gray area). The short dashed line indicates a local minimum where two MUs were merged into one.

Figure 3.

Motor planning (initiation) in LL and EL infants. Heat maps on the ball’s position on the trajectory relative to when the transport unit (TU) started and the hand position at TU start (mean denoted by +, whereas ellipses show standard deviation in x and y dimensions). (a) Normalized heat map displaying ball’s X- and Y-position on the trajectory when the TU started in the LL group. (b) Normalized heat map showing the ball’s position on the trajectory when the TU unit started in the EL group. (c) Normalized difference map highlighting the group differences on the trajectory relative to when the TU started. (d) Initiation as a function of group (measured in distance to target, mm, at the onset of the TU of the reach). *p < 0.05.

Figure 4.

Prediction in LL and EL infants. Prospective aiming operationalized as how far along the future trajectory of the ball (expressed in ms) the reach is directed. Thus, a score of 1000 ms means that an infant directed his or her reach toward a position the ball would be in 1000 ms. Error bars represent standard errors. Circles represent averaged individual data points.

Figure 5.

Analysis of movement units (MU). Illustration of main kinematic variables shown by averaged individual data points: (a) Transport unit (TU) peak velocity in mm/sample for the LL and the EL group. (b) TU distance traveled in mm for both groups. (c) Straightness of the TU for LL and EL group. (d) Number of MU during the reaching movement for LL and EL group. *p < 0.05. **p < 0.01 in main analyses. Error bars represent standard errors.

Figure 6.

(a) Scatterplot of number of movement units (MU) against the Early Learning Composite Score on the MSEL with separate regression lines for each group (due to the significant interaction term; see main text for details). (b) Scatterplot of distance traveled (of the TU) against the Early Learning Composite Score on the MSEL with a regression line for the total sample. (c) Scatterplot of peak velocity (of the TU) against the Early Learning Composite Score on the MSEL with separate regression lines for each group. Full circles represent trials of LL infants, whereas open circles represent trials of EL infants.