Special cameras track the position of markers in 3-dimensional space in a room. The markers look like small, reflective balls (between 1.5 and 10mm across) and we fasten them with lightly adhesive tape to, for example, children’s hands. This gives us the possibility to study hand movements with high precision.
With help of markers on children’s hands and other places on the body, we can examine how children plan and carry out their actions. We often use the velocity curves of the markers to examine what children expect to happen, for example the path of a rolling ball.
We also use the system to make films for other studies. We fasten markers to an actor’s joints and only show children the movements of the markers. This is a way to reduce visual information in a film, allowing us to focus on how children perceive the movements of individual points as a cohesive whole.