A Comparison of Object Exploration Strategies Between Infant Siblings of Children with Autism and Typically Developing Infants at 6 Months of Age

Background:

Infants significantly improve their ability to explore objects multi-modally (i.e. oral, visual, and manual) after the onset of reaching at approximately 5 to 6 months. Between 6 and 12 months, infants will differentially manipulate objects based on properties such as shape, weight, and texture (Ruff, 1984). Infants who later develop autism spectrum disorders (ASD) are known to have fine-motor delays as early as 6 months (Landa and Garrett-Mayer, 2006).

Objectives:

The goal of the present study was to identify object exploration deficits in a cohort of infants at risk for autism (i.e. infant siblings of children with autism (AU sibs)) as compared to typically developing infants at 6 months of age.

Methods:

13 AU sibs and 15 typically developing (TD) Control infants between 6 and 7.5 months of age were observed during an object exploration task. Infants were offered 2 circular (2 inch diameter) and 2 long rattles (4 inch long) that made a noise on shaking. We contrasted long and circular rattles because circular objects require more bimanual coordination for exploration than long objects. The rattle was offered near the infants' hands so that they could easily grasp it without having to reach too far. If the rattle dropped out of their hand, the tester picked it up and offered it again. Infants’ exploration behaviors were videotaped and coded later. We coded for duration of grasping with one or both hands and duration of looking and mouthing. In addition, we coded the frequency of transfers from one hand to the other and the frequency of rhythmic arm movements such as shake, bang and rotate. Coders maintained intra-rater reliability of 95% or above for all duration and frequency codes.

Results:

For the circular rattles, AU sibs had significantly shorter grasping durations (p=0.04) as compared to Control infants. For long rattles, while there were no group differences in grasping durations; AU sibs had significantly fewer transfers (p=0.04) from one hand to another as compared to Control infants. We did not find statistically significant differences for durations of mouthing or looking as well as for the frequency of rhythmic arm movements.

Conclusions: AU sibs had difficulty manipulating objects that required greater bimanual coordination such as circular rattles. They also showed fewer transfers of the long rattle from one hand to another. This further confirmed that AU sibs may have impaired bimanual coordination as compared to Control infants. In contrast, to the past retrospective reports of excessive mouthing in infants who later develop ASD, we did not find significant differences in mouthing durations. However, there were statistical trends for greater looking durations in the AU sibs group. Together, these data suggest that fine-motor deficits in bimanual coordination may be a feature of the broader autism phenotype. Furthermore, these preliminary results implicate the need for larger studies on fine-motor development of AU sibs. These data also emphasize the need to include object exploration behaviors within early assessment and treatment protocols of ASD.