Thursday 4 November 2010

On being (briefly) unimanual - and worse, right handed!

Six weeks ago I broke my left wrist playing soccer. For the first two weeks I was in the temporary cast from the Accident & Emergency ward. It was only supposed to be a couple of days, but I had to travel to the US before my appointment to get a proper cast. I therefore had this unwieldy cast on while everything was sore, rendering me effectively one handed. The real cast was lighter and gave more support, and enabled me to use my arm more; the wrist was still constrained, though, and so I still had to rely on my (non-preferred) right hand for many tasks. I'm out of the cast as of Tuesday, although I need to rehabilitate the muscles back before I'll be 100%.

The experience has been quite interesting (in between being very boring). I've observed transfer of learning, recalibration of my arm as effector, and adaptation of numerous actions to the point where I can't really remember what it felt like to do them prior to the injury. I'm going to have to spend some time going back again now the cast has come off, and these things all touch on the topics I'm interested in covering on this blog.

A caveat: the plural of anecdote is not data. I'm not trying to convince anyone of my interpretations here, just thinking about my experience through the lens of my theoretical understanding of perception/action.

1. Transfer of learning
I'm left handed, which means my preferred hand has been out of action and I've had to learn how to use my right hand to do a lot of things. I'm very left handed, and my right hand is generally a bit useless. Spending two weeks with the clunky cast meant I was properly unimanual for a while, so I had no choice but to do things with my right hand. The result is that I can now brush my teeth, carry a cup of tea and handle a fork with my right hand pretty proficiently.

Teeth: When I started out I had no sense of how big my mouth was, and so spent a few days pulling the brush too far out of my mouth and banging my teeth on the way back in. Every movement was very slow and deliberate. Now, after 6 weeks, the whole operation feels entirely normal.

Carrying Tea: I've tried carrying hot drinks in my right hand before, and invariably it's wobbled and rocked until I've spilled some. In my left hand, I've noticed I make smooth corrections that simply damp the vibration out of the liquid; about 10 minutes ago, I watched myself carrying tea in my right hand as smoothly as that. I also cope with perturbations well now: passing through doors, etc, I can keep the tea steady and not have the forces involved in interacting with the door affect it at all.

Forks: For the first two weeks I simply couldn't figure out how to hold a fork in my right hand in anything other than a power grip.This meant I had none of the usual control available via my fingers, and frankly it was all a bit clumsy and ineffective. One day I simply found I had picked the fork up in a much more useful grip and it was then just a matter of getting better.

I've gone from utterly useless to fairly proficient in a remarkably short period of time. A big part of this is that I have already acquired these skills for my other hand; the savings I'm seeing reflect transfer of learning. Such transfer suggests that whatever it is that enables me to do this typically isn't specific to my left hand. Traditional accounts of transfer suggest that what is learned is an abstract, effector independent representation of the task, which I have simply plugged into my right rather than my left hand. These representations are often described in terms of generalised motor programs or schema (Schmidt, 1975). These programmes are general, in that they don't contain instructions for making a specific limb do something; rather, they contain instructions for the end result, and you parameterise them at the time of execution. This is of course nonsense. Skilled action is not the end result of a motor programme, it emerges from the interplay of environmental, organismic and task constraints. The savings reflect, I think, primarily perceptual learning (of the information required to control the action). The fact that transfer wasn't instant suggests it takes time to learn the effectivities of my other arm and to assemble the new overall device. But I do still think that the question of 'what, precisely is it that we acquire during learning' is an interesting one. A big push for things like motor programmes and representations is to explain how things remain the same across varied contexts. Part of the ecological answer is that the contexts aren't that varied: a given task will contain the same information to support action, for example, and the things that vary are just noise. But I find this an interesting challenge to ecological theories and something I want to invest time in in the future.

2. Recalibration
Smart devices need calibration. Calibration is the process of aligning the output of one system to the output of another, known system. In perception/action, this entails adding meaningful units to a measurement, and this process is always ongoing. For example, one common calibration is to come to visually perceive distance in terms of an action capacity, such as arm length. Without calibration, visual information is angular and ordinal; you can see that one thing is in front of the other and the heading, but not the metric distances. Calibration of the smart device perceiving distance means that the output of that device is expressed directly in terms of, say, arm lengths, or (for further distances) eye heights. You calibrate a system like this with feedback: the initial reach to an object is made using the uncalibrated information and then guided visually to the goal at the end of the movement. Once you have reached the goal, you can now reach to that spot again without additional feedback (for a while). Try this: reach for an object on your desk with your eyes open; then bring your arm back, close your eyes and repeat the reach. You will be very close to where you want to go, and this ability will persist for a short period (e.g. Mon-Williams & Bingham, 2007).

Once I got the new cast, my arm was fairly mobile and more or less usable; the bone was healing and the cast supported my wrist enough. But the constant presence of the cast changed my arm's characteristics; it's a bit bigger, more rigid, it weighs more and moves differently. Effectively, I have a new ruler, one with slightly different units than my arm by itself. Over the weeks I became more and more at home in my cast, so that  my arm moved very differently than it used to but with skill and confidence equivalent to what I have with my arm normally. Not only have I recalibrated, but that recalibration has shifted my 'typical' calibration by virtue of being constantly required, and as far as my perception/action systems are concerned, my arm just moves this way (in a more robust version of what happens when we pick up tools). I have very little memory of it being different, and it mostly doesn't feel strange any more (unless I'm doing something such as typing, where the new constraints are a significant hindrance). In a very real sense, I am going to have to relearn to use the old arm, although I'm willing to bet the savings will be even more significant.

With this recalibration has come a change in the way I effect affordances. My typing has evolved into a fairly fast but slightly odd looking style to reflect the fact I can't bend at the left wrist. Things that are placed on a high shelf no longer look pick-up-able to me with my left hand because they require wrist movements I can't currently manage. My day to day interactions with objects all now reflect my new effectivities, and although it's not perfect I move and act quite smoothly with respect to what my arm allows. This is especially obvious when I think back to the first few weeks and how I had to constantly stop and deliberately re-do actions my broken wrist wouldn't support; I now spend the vast majority of my time selecting entirely appropriate actions and I've often unaware that there's anything 'different'.

Use dependence in muscles
One of the really weird things about having your arm in a cast for 6 weeks is how atrophied the muscles become.
My weirdly small left hand and forearm
Muscle size and shape is highly use dependant, as you can clearly see from the various type of athletes that there are in the world. Swimmers are an entirely different shape from weight lifters, for example. But it's odd to see it on this scale in yourself and in this direction. The biomechanical and physiological infrastructure supporting our action capacities are use-dependant in a similar way to, say, cortex. Recall how cortex ebbs and flows to reflect current use, the presence of tools, etc. I don't think the brain is representing anything; but I do think that it might be the fast-switching component that allows us to form, disassemble and reassemble various task specific devices (Bingham 1988) at the speed we do. My body ebbs and flows in the same basic way, but with it's own dynamic (time course) that reflects the properties of the cells and materials involved. We are the basic shape we are because we're human rather than something else; but we are the specific shape we are because of what we do.

Some conclusions
As tedious as this broken wrist has been, it's been an intriguing experience for a perception/action nerd.

1. My arm in the cast has become the norm, and I don't really have any 'memory' of it being different. Obviously I recall a time when I wasn't in a cast; but I can't conjure up how my arm felt then. I'm resonating to my current informational environment, not representing and storing experiences like a computer.

2. Savings aside, it's taken a lot of practice to improve and none of the changes in my left arm happened until I got the new cast and could move that arm. Movement creates the information about the characteristics and capabilities of a limb.

3. Calibration studies typically involve a brief period of (say) wearing prism glasses and reaching under the altered conditions until you are moving appropriately. You then take the glasses off and watch how long the re-adaptation takes (it's always less time). I've spent a long time adapting (6 weeks!) and it will be interesting to see how hard it is to re-adapt. It would also be interesting to see if the learning is retained.

Future posts will talk about task specific devices, specifically the Bingham (1988) paper which rocked my world in 2001 when I read it while writing my qualifying exams; calibration is also a fascinating topic which becomes crucial when considering perception/action systems as smart, dynamical devices.

Bingham, G.P. (1988). Task specific devices and the perceptual bottleneck. Human Movement Science, 7, 5-264. DOI

Mon-Williams, M. & Bingham, G.P. (2007). Calibrating reach distance to visual targets. Journal of Experimental Psychology: Human Perception and Performance, 33(3), 645-656. DOI

Schmidt, RA (1975) A schema theory of discrete motor skill learning. Psychological Review, 82(4), 225-260. DOI


  1. Skill comes with practice. End of.


  2. Agreed, but where does the practice go so I can use it again?

  3. I'd be quite interested to know if there was anything you feel didn't improve as much as you would have expected it to? Did writing transfer nicely? (not that we ever have to write any more...

    what about bimanual combo tasks, like buttoning a shirt or tying shoelace? Were you able to switch around the action and the support hand, or were you just able to fumble through with the same configurations as before?

  4. Writing: not even a little bit, although I didn't try that hard because it was failing so hard. I can barely figure out how to hold the pen in my right hand.

    Things I did a lot (carrying tea/coffee, cleaning teeth, etc) all actually became pretty good. The only things that didn't improve were things I didn't do that much.

    The bimanual stuff: that's a good question. Thinking about it, I didn't switch which led and which supported, I just fumbled through. Shoelaces were impossible early on because the broken bone didn't let me generate enough force (thanks Sabrina! :) but when I could do it it was the normal way round. Interesting - it never occurred to me to change that!

  5. Oh joy, I did it again (damn you ice!). Well, I do always tell my students that the most important session in a learning study is the retention session you do much later on to see what stuck...