Coordination is everywhere we look. We coordinate our limbs when we walk. We coordinate our fingers when we write. We even coordinate our movements with another person’s movements.
The study of coordination has been coined “coordination dynamics”. In the book “Coordination Dynamics: Issues and Trends” (2008), Scott Kelso, a leading figure in the field, described the science of coordination dynamics as:
“It explicitly addresses coordination within and between levels of description and organization. Coordination Dynamics thus aims to characterise the nature of the coupling within a part of the system (e.g., the firing of cells in the heart or neurons in a part of the brain), between different parts of a system (e.g., parts of the brain, parts of the body, members of an audience), and between different kinds of systems (e.g., stimuli and responses, organisms and environments, perception and action, etc.). Ultimately Coordination Dynamics is concerned with how things come together in space and time, and how they split apart.”
The purpose of this article is to provide an introduction into coordination dynamics.
Let’s do a task. Place both hands out in front of you with your palms facing each other. Clench all of your fingers except for your index finger – the index fingers need to be extended. Now, your task is to move each index finger towards each other at the same time. Then, move each finger away from each other at the same time. Do this repeatedly without any pauses. You should find this task very easy. Now try doing it as fast as possible. Notice that you should still be able to accomplish the task with ease.
Now, lets do the opposite. Your aim is to move both fingers in the same direction For instance, when you move the left finger towards the left, your right finger should also move towards the left, and vice versa when moving to the right. Do this slowly at first. Again, you should find this to be a fairly simple task. Now try to do it as fast as possible. What you will probably notice is that you will change from both fingers moving in the same direction to each finger moving in the opposite direction (i.e., as per the first task above). This is a classic bimanual coordination task.
Why does this occur?
We all have coordination tendencies, also referred to as intrinsic dynamics. For most humans (if not all), moving each index finger in the opposite direction, or the same direction, at the same time, are coordination tendencies. These are also referred to as “attractor states”.
For bimanual coordination tasks, at least 2 attractor states are found. An “in-phase” pattern and an “anti-phase” pattern. The in-phase pattern is characterised by the movement of fingers in the opposite direction (i.e., the easier task at high speeds), whereas the anti-phase pattern refers to the movement of fingers in the same direction (i.e., the more difficult task at high speeds).
For the finger task described above, the in-phase pattern is a more stable attractor state. This means that when the movement is challenged, such as when speed increases, the movement pattern reverts to this attractor state.
Can attractor states change?
Yes. A number of studies have demonstrated that attractor states can change with practice. Learning a new coordinative pattern temporarily destabilises previous attractor states so that a new attractor state can emerge. Hence, instability in the movement system should be viewed as an important step before developing stability. Stabilising new coordination patterns (due to practice) increases the number of coordinative patterns available to perform the task.
What does this mean for complex movements?
The task described above involves minimal degrees of freedom in the movement. However, many movements in everyday life involve coordinating many degrees of freedom. This does not mean that the study of finger movements is irrelevant. It simply means that the study of complex movements is more challenging, as researchers need to identify the important coordinative structures amongst many possibilities in the human body.
Coordinative structures (also referred to as synergies) are functional groupings of structural elements. For example, in the task above, movement of the 2 index fingers represents a coordinative structure.
Future articles will discuss the study of coordination dynamics in complex movements.