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!


Instruments as (complex) landscapes

Today, I attended a very interesting seminar by Dr Scott McLaughlin at the Sonic Arts Research Centre, titled ‘Material Cartographies as Composition’. Scott discussed his approach to musical composition, which involves using multi-stable/chaotic properties of instruments or sound-producing materials (e.g. mics and speaker feedback) as the basis of his compositions. The complex interactions between performers and such chaotic or multi-stable systems forms the topology/cartography/landscape* over which each piece unfolds. A key idea is that once a landscape of interaction is set-up, e.g. by bringing a skilled musician to an ‘instrument’ that responds in a determinate-but-chaotic way, unpredicted sonic things can happen within a reasonably constrained set of conditions. A nice example presented was of a guitar player controlling feedback by moving the guitar around in front of an amplifier. This has the effect of changing the pitches of the feedback in ways that are constrained by the laws of physics, but which are not straightforward to control, given all the complex parameters involved (guitar string tension, resonant frequencies, millimetre distance between guitar and speaker, etc.).

I liked Scott’s approach, particularly the fact that he seemed to have a genuine interest and respect for the ideas he imports from complex systems theory, rather than merely applying the terminology in its colloquial use. However, one question which I had was the degree to which these instruments or landscapes are learn-able to a performer. That is, are the compositions simply the accidents of imparting energy into a complex responding system, or could a user acquire some degree of mastery of the systems? This is an important question for me, coming at this from the perspective of a psychologist interested in skill acquisition. Understanding if and how musicians can learn to perceive and manipulate the regularities (invariant patterns) in complex systems may help in understanding skilful adaptability in lots of areas of life, not just in experimental music.

Part of Scott’s answer to this question, which I think is a useful starting point, is to think of games. Take card games. Even though the rules of a game of poker might be constant, no two poker matches are identical**. Hence, individual poker matches are deterministic but chaotic systems (in some description). When people first start to learn the game, play often faltering, clumsy, and unsatisfying. Over practice, as the patterns and outcomes become perceivable and players learn to detect and act on these, more fluid and satisfying play ensues. In a sense, skilled poker players are experts in managing chaotic, complex systems. While this is a useful analogy, card games generally do have a number of explicit rules which can anchor the learner in discovering the more complex patterns that emerge during different iterations of game-play. With highly indeterminate, complex systems – like some of the instruments Scott described – it is not quite as clear what would anchor a musician’s behaviour in order to get the process of learning off the ground.

Another point Scott made would be that the cultural context of practice in which the musician is skilled, and in which the performance occurs, may also constrain this process. This is a very interesting idea, one that I have become increasingly interested in. However, my challenge, as a psychologist, is going to be figuring out how to scientifically research such a multifaceted problem. This issue is something I will probably devote quite some space to on this blog towards, in the hope of get this research question off the ground.

A final point from today’s seminar that I want to mention here is Scott’s response to a question from Paul Stapleton. As Scott was talking, Paul and I were sat next to each other, and a number of times we spotted ideas that resonated with our own discussions around musical improvisation and skilful adaptability. Paul asked why Scott had not mentioned ‘improvisation’, given how relevant it seemed to the ideas in the seminar. Scott replied that he had found that when he tried to explicitly instruct musicians to improvise in his topology/landscape compositions, the results had generally been ‘shit’. This creates a very interesting question about improvisation as something that interaction within a complex system requires (to manage all the unpredictable fluctuations and chaotic behaviours) versus improvisation as intentional variation within a relatively stable, predictable set of constraints. I cannot yet decide if these are two separate senses of ‘improvisation’ or two flavours of a common concept. Hmmm….


*these terms were used semi-interchangeably, with acknowledgment of important conceptual distinctions

**this is true, at least in part, because the likelihood of two shuffles of a deck of cards producing the same ordered deck is astronomically small.