We offer you a hand coordination game, which has gone viral on the web in recent weeks, in which participants are asked to touch a sequence of sheets using different combinations of fists and open hands.
We start from the bottom, open the hands where there is the drawing of the open hand, and close the fist where there is the circle. In total there are four combinations between two open hands, open hand and closed fist, two fists.
Although the rules are extremely simple, many people fail after the first steps, making obvious mistakes even though they know perfectly well what gesture they should perform.
The difficulty of this task has to do with how the human brain organizes and controls movement.
The brain works in a “cross” manner
A first fundamental aspect is the organization of the motor system. In the human brain the control of movements is predominantly contralateral: The left hemisphere controls the right hand, while the right hemisphere controls the left hand.
This organization works extremely efficiently when both hands perform the same movement, because the two hemispheres can work in synchrony.
When the hands have to perform instead different movements at the same timeeach hemisphere must carry out a distinct motor program, keeping it separate from that of the other side.
Symmetry is the “default” option
From a neuromotor point of view, symmetrical movements are more stable and less costly. Clapping your hands, clenching both fists or opening both hands are highly automated gestures, learned early and consolidated over time.
The brain therefore spontaneously tends to synchronize the two hands. This tendency is so strong that, in the absence of active control, one hemisphere can “drag” the other towards the same motor pattern, even when the rules of the game require the opposite.
The key role of inhibition
The central point of the game is not so much the execution of the movement, but the need to inhibit motor automatism. When one hand must make a fist and the other remain open, the brain must:
- activate the correct movement for each hand
- block the reflex that would lead both to make the same gesture
This control and inhibition function is not carried out by the primary motor areas, but by the systems executive controlwhich operate at a more abstract level and supervise the movement. Inhibition requires cognitive resources, attention and continuous monitoring. It is not an automatic process, and tends to deteriorate rapidly as cognitive load increases.
Because you make mistakes even knowing what to do
An interesting aspect of this game is that people often make mistakes even though they understand the rule perfectly.
This happens because the knowledge of the rule is explicit and conscious, while the execution of the movement is largely automatic. When the control system can no longer keep the two motor programs separate, the brain simplifies and returns to the most stable pattern: symmetrical movement. The result is an error that does not arise from mental confusion, but from a physiological limit of human motor control.
