During a free-falling catching task, the brain manages to made prediction of how long does it takes to the ball to touch the hand. Lacquaniti and Maioli (1989) had shown that this prediction is characterised not only by an anticipatory activation (about 100 ms before impact) of EMG signals recorded on flexor muscles of the elbow, but also by a variation in the intensity of activation, proportional to the impact of the ball in the hand. Since their protocol do not permit to analyse precisely what information is involve in this process, we performed a similar protocol with new devices.
Six volunteers were asked to catch a Silicon® ball projected threw the floor by a launcher which opening was at 1.6 m high above the hand of the subjects. We have used 3 initial speeds of release (to simulate different heights of falling). Accelerometer (on the hand) and EMG data of biceps brachii were synchronised and recorded by mean of an optokinetic system (Kinelite®, sample frequency : 800 Hz).
Anticipatory activity of biceps brachii began before ball impact and intensity of muscle activation was proportional to momentum of the ball (i.e. mass x velocity, that became impact variation if expressed relative to time).
As the height of the release does not change, it would seem that visual information
is use in that task. Nevertheless, different models based only on visual cues
or variables failed in predicting our results. As a matter of fact, the ball
does not fall at constant velocity and the trajectory is not perpendicular to
the front plan of the subject.
So, integration of visual information might be coupled to proprioceptive and
gravitational information together in an internal model which allows anticipating
of the perturbation due to ball impact in the hand and production of the right
muscular activity at the right relative time.
Lacquaniti F. & Maioli C. (1989). The role of preparation in tuning anticipatory and reflex during catching. J. Neurosci., 9: 134-148.