Reaching While Learning to Sit in Infants at Typical and Elevated Likelihood of Autism

• In Event: Novel Findings and New Methods in Motor Skill Development, Perception, & Learning

Abstract

Although infants begin to reach before they sit independently, reaching and sitting are co-developing behaviors. Newly sitting infants must coordinate reaching with upright postural control (e.g., Harbourne et al., 2013), and the challenges presented by independent sitting may temporarily disrupt reaching movements. Compared to neurotypical peers (TL; typical likelihood), infants with an elevated familial likelihood (EL) of autism spectrum disorder (ASD) spend less time in independent sitting (e.g., Leezenbaum & Iverson, 2019), exhibit reaching delays at 3 months (Bhat et al., 2009), and perform worse on fine motor tasks at 6 months (Iverson et al., 2019). The present study examined infant reaching in supported vs. unsupported sitting longitudinally during the transition to independent sitting.

Forty-four infants (20 EL, 24 TL) were observed every two weeks at home from 2.5 months until one month after sit onset (i.e., sitting without support for 30s). The present study focused on data from 6 biweekly sessions spanning 1.5 months before to 1 month after sit onset. Kinematic data were collected to explore potential interactions between reaching and upright postural control. Infants wore magneto inertial sensors on both wrists and were positioned on a Tekscan BPMS 5315 pressure-sensitive mat, first in supported sitting (SS; supported around the hips), then unsupported sitting (US). In each posture, there were four 30s trials with a toy presented at midline. Primary reaching variables were Duration (the moment the hand started moving toward the toy until first touch) and Mean Squared Jerk (cm2/s5; lower values correspond to smoother arm movements). To examine postural control during reaching, we identified segments of center of pressure (CoP) data corresponding to reaching movements and calculated Total CoP Displacement (cm; lower values correspond to greater stability during reach).

EL infants achieved sit onset significantly later than TL infants (p = 0.028; Figure 1). To examine developmental change in the primary variables in SS and US, Hierarchical Linear Models were calculated with time centered at sit onset. For US, analyses begin at 0.5 months pre-sit-onset when most infants were able to remain upright. Preliminary analyses with 30 infants (13 EL, 17 TL) revealed no significant differences in intercepts or slopes between EL and TL infants, so groups were combined. Reach Duration remained stable across the transition to independent sitting in both postures (Figure 2a). There was a significant negative slope for Mean Squared Jerk in both SS and US, though reaches in US were less smooth overall than those in SS (Figure 2b). Across sessions, Total CoP Displacement during reaching decreased in SS (p < 0.05) and US (p = 0.053), though infants were more stable as they reached in SS than US (Figure 2c).

Although EL infants achieved independent sitting later than TL infants, they exhibited similar patterns of change in reaching and sitting. Reaches became smoother and sitting more stable across the transition to independent sitting, but reaches produced in US were less smooth than those in SS. Findings will be discussed in terms of the dynamic relations between emerging skills and well-established behaviors.

Authors

• Emily Roemer Britsch, University of Pittsburgh
  Presenting Author

• Joshua L Schneider, University of Pittsburgh
  Non-Presenting Author

• Valentina Focaroli, Universita' Campus-Biomedico
  Non-Presenting Author

• Fabrizio Taffoni, Università Campus Bio-Medico
  Non-Presenting Author

• Flavio Keller, Universita' Campus-Biomedico
  Non-Presenting Author

• Jana M Iverson, Boston University
  Non-Presenting Author