Our senses limit our actions, and this is a good thing

It can be so helpful sometimes to revisit older texts that were part of your intellectual trail, but which haven’t been retread for a while. Today, I met with my PhD student Alannah to discuss a book chapter by Karl Newell, ‘Constraints on the Development of Coordination‘. The last time I thought about this paper properly was when Johann Issartel and I set out to write a critique of it 10 years ago (this has yet to materialise, but may happen yet), and I haven’t looked at it since then. Alannah’s project is about motor development in children with visual-impairment, and so it seemed like a relevant source of theoretical ideas for her thesis, and something that would be worth discussing. I’m very glad we did.

The paper sets out a theory of the development of coordination, essentially the principles by which children come to acquire skilful control of their movements. A central idea is as follows. There are too many ways to move. All the possible ways of rotating joints, contracting or relaxing muscles, and shifting limb parts through space, means that there is a huge mathematical problem for the developing brain to solve: how to reduce these possibilities from an infinite set to a workable set for controlling intentional behaviour (this is a crude summary of Bernstein’s Degrees of Freedom problem).

Part of the answer to this problem lies in the concept of ‘constraints‘. Constraints are limits on how physical things can move. Gravity. Limb mass. The material springiness of connections between muscles, ligaments, tendons, and bones. Boundaries of frequencies of signals to and from the central nervous system. The properties of structures, objects and events in the immediate environment. All these things reduce the degrees of freedom available. Thus, coordinated behaviour emerges from how different constraints force organisation of the component parts involved. As a somewhat removed illustration, a murmuration of starlings emerges from the combined constraints of gravity, air-flow, wing shape, and a few simple (though yet undiscovered) rules governing how each bird responds to motions of other birds in their visual field. Rather than thousands of birds all flying around at random, these constraints limit their possible paths of motion to a smaller subset of codependent trajectories. The results is a beautiful, coordinated complex system (see video below). The idea is that human (and other animal) movement obeys similar natural laws, whatever they may turn out to be. Thus, the concept of constraints on coordination provides a starting point to a solution to the Degrees of Freedom problem. This idea is summarised nicely in a line quoted from another paper by Kugler, Kelso and Turvey: “it is not that actions are caused by constraints, it is rather that some actions are excluded by them”.

Importantly, information picked up through our senses can also constrain movement. That is, when functioning to guide action, vision/audition/proprioception/etc., all limit the range movements that can/should be made. We tested (informally) this idea today, by having me close my eyes and draw a figure-of-eight in the air. When I made the same movements with eyes open, the pattern was more accurate, and consistent. The set of finger movement possibilities was reduced by the visual constraint of how my limb moved in relation to the intended pattern. Perception limits action. This brings me to a ‘Eureka’ moment I had when re-reading the paper, and which Alannah and I discussed in earnest today.

Visual-impairment is not a constraint on coordination, but rather a reduction in constraints. Having limited or no visual access to one’s own limbs, or objects/structures/events in the environment, does not limit movement but rather removes a limit on movement. Thus, movement development is affected by having fewer informational stabilisers and contours to follow.  Of course, other modalities (audition, proprioception, etc.) can and do impose constraints on movement, and optimal patterns of coordination may be discovered by someone with visual-impairment through these limiters. The goal now becomes identifying the best ways to organise task and environmental constraints to help the children uncover these solutions, rather than trying to replace visual ‘input’ through other channels. As a result, thinking about vision and other senses as limitations on movement will really shift the way Alannah and I have been viewing perceptual motor development in children with visual-impairment.

(Re-)reading older papers is a good idea!

Musicians keeping together in time

I gave a guest lecture yesterday on the topic of ‘Action’ in Music Psychology. This was for a colleague/friend, Trevor Agus, who runs a course called Music Psychology for students enrolled on Music programmes in the School of Arts, English and Languages. We amuse ourselves that he teaches Music Psychology to music students, while I teach Psychology of Music to psychology students. This was the second time I have given this class.

It is an odd thing for me to teach a class on Psychology of Action to music students, not least because I almost could have become a music student myself at one point in my life. Instead, I became a student of philosophy and psychology, and then movement, and then movement in music, etc. Ah, well. It feels very different trying to impart a message about motor coordination and skill acquisition to musicians than to impart the same message to psychologists. The things that feel the need for emphasis differ, and the ideas that capture the room differ too.

One idea from the class that I was happily reminded of in preparing for it is the complex challenge of musicians coordinating with each other in ensemble performance. It is a miraculous thing enough that one nervous-muscular-skeletal system can coordinate its own behaviour to give rise to musical performance, but it is even more miraculous that many of these systems can not only coordinate their own sounding actions, but also coordinate with each others’ actions. Much of the research into this phenomenon is focussed on either measuring timing between musicians (e.g. the correlations of note interval variations between musicians), or on identifying the perceptual signals that might support musicians in the task of interpersonal musical coordination. In the latter case, the visual cues from body movements and gestures (both intentional and unintentional) seem to play a pretty big part in helping musicians to stay coordinated with each other while enacting a performance.

An example of this that I used in the class is from a concert by the Penguin Cafe Orchestra filmed for the BBC in the mid-80s. In the performance of Air á Danser, a section of the piece involves the group slowing down together a couple of times, then speeding back up to resume the flow of the music. Simon Jeffes, the leader of the group, conducts this process through a combination of head movements, eye contact and body gestures, with the result that around a dozen separate musicians are able to control the timing of their actions as a single unified system. The video clip of the whole track is embedded below, and the section in particular begins at around 1:05. It’s a lovely example of multisensory interpersonal coordination in musical performance, as well as being a very charming piece of music (in my opinion, at least).