This deliverable describes the efforts made in task T1.2 “Laboratory experiments on small groups”. The goal of this task is to conduct experiments under controlled laboratory conditions with individual participants or small groups that help to fulfill the objectives of WP1.
In crowds, people are often being pushed from different directions and in situations when people are faced with strong external perturbations, they need to adjust their postures immediately to reduce the risk of falling. If one falls in the chaos of the crowd, there is a high risk of injury and even possible fatal outcomes. Therefore, to avoid falling one needs to have a well-developed skill to maintain balance via postural control which effectively ensures that the body’s center of mass remains within its base of support. This can be done by using different postural strategies following (reactive postural control) or even preceding (anticipatory postural control) such perturbations.
Therefore, our focus is to observe and measure postural control in balance-perturbing situations. Specifically, we are using external perturbations such as a push at the back of the participants to elicit both anticipatory and reactive postural control responses. By repeating these perturbations in 10 to 30 consecutive trials we challenge the participant’s neural control of movement and expect to elicit a learning effect. That is, we expect the participants to gradually learn how to react faster and appropriate to such perturbations in order to maintain their balance.
We intend to apply such perturbations either manually (i.e., pushing with a hand by the examiner or another participant) or by using a newly designed and built mechanical perturbation device which allows more control over the pushing force. The perturbation device would be especially useful in the experiments where we plan to induce a series of consecutive perturbations with the same push profile (velocity and magnitude of the applied force). In any case of either manual or mechanical perturbation, the magnitude of the pushing force never presents any health hazard to the participants. Namely, the intent of these perturbations is to manipulate balance of the participants in a way that in case of a loss of balance, the participants will be able to regain their balance by simply changing their posture (bending in knees or/and hips) or in most extreme cases making a step.