Behavior Coding
The experimental tasks were coded for four behavioral measures: success, adult assistance, hand actions, and time to plan and execute the task. Each behavior measure was scored by two coders to establish interrater reliability for 30% of the dataset. Interrater correlations were > 0.85 for all the measures (Success = 1, Assistance = 0.87, Hand actions = 0.88 to 0.96, Planning time = 0.92, Execution time = 0.85).
Success : Success was defined as the child opening the lid of the box and taking the toy out. If after opening the lid, children used other strategies such as vigorously shaking the box, knocking over the box, or dumping the contents onto the table, it was considered successful. Additionally, if children required partial assistance from the adult experimenter (see definition below) to retrieve the toy, it was scored as success. We are reporting on the percentage of children in the DS and TD group who succeeded in the experimental tasks.
Adult Assistance : Adult assistance was defined as the physical help provided by the experimenter to retrieve the toy from the box. Assistance was scored as 0 (no assistance) if the child independently retrieved the toy from the box, 1 (partial assistance) if the child required help from the experimenter to stabilize the box while they opened the lid and/or took the toy out of the box, and 2 (total assistance) if the child was unable to complete the task on their own and required help to open the lid and take the toy out. We are reporting on the percentage of children in the DS and TD group who required no, partial, and total assistance for the three tasks.
Hand actions : Child’s use of hands was scored as unimanual if they used only one hand (right or left) and bimanual if they used both hands while completing the task. Bimanual actions were further categorized as symmetrical or asymmetrical. Symmetrical bimanual actions indicated using two hands to perform a same action, e.g., opening the lid of a box with both right and left hand. Asymmetrical bimanual actions indicated using two hands to perform different actions, e.g., holding the box with one hand and opening the lid with other. We are reporting on the total frequency of unimanual, symmetric bimanual, and asymmetric bimanual actions for the experimental tasks.
Planning and execution time : Planning time was the time required to plan actions and was scored as the time taken by the child to make first manual contact with the box after the experimenter placed the box on the table. Execution time was the time required to complete the task and was defined as the time taken to open the lid of the box after making first manual contact with the box. Execution time was not scored for children who were unsuccessful in opening the lid and/or required total assistance. We did not consider the time taken to take the toy out of the box within the execution time as there was lot of variability in the strategies used to take the toy out of the box. For example, some children quickly dumped the toy on the table after opening the lid vs others took time to carefully scoop the toy out using their fingers. We are reporting on the planning and execution time in seconds for the three tasks and the total time.