Tuesday 14 November 2023

Do Affordances Select or Control Actions?

I've been working for a while to connect the perception of affordances to motor abundance methods such as the uncontrolled manifold. I proposed the idea in this book chapter, and then I have a paper under review that is my first swing at making this work; the details of the hypothesis are in those, and I recommend you read them. The paper in particular has my most recent thinking spelled out as clearly as I can in the Introduction and Discussion sections. 

As I've been chatting to people about progressing this programme, one thing that keeps coming up is 'why has no-one thought to do this before?'. This link simply seems so obvious to me, and to the people I'm talking to, but no-one has done it. I think I may have figured out why, though, and I thought I'd document the reason because I'm a sucker for these kinds of mysteries, especially when I think I've solved them. 

I think the reason no-one has thought to connect affordances to UCM is that (almost) no ecological psychologist has been studying affordances as a solution to the control problem! Affordances are studied as solutions to the action selection problem only, and this seems to come from Warren. I'll link to some papers and lay out some thoughts for the record here. 

I have always thought that Fajen's affordance-based control framework had obvious connections to what I was doing with affordances and UCM. I was re-reading his 2005 paper the other day and came across an interesting section; Information-based control and affordances, pg 390. I'll quote it in full, because it stuck out in a way it never had before now this question is on my mind

The incompatibility between information-based control and the theory of affordances is reflected in Warren’s (1988) framework for visual control, in which the affordance problem and the control problem were described as separate components. Warren proposed that actors first choose an affordance to be realized, which establishes a corresponding mode of action. Once the affordance is chosen, the task-relevant parameters on the action side are regulated by optical information according to some law of control. Such laws of control take the specific form that is found in information-based models described earlier; that is, they describe how the task can be performed by moving so as to produce a particular pattern of optic flow. Thus, the control problem (i.e., how actions are guided on the basis of visual information according to some law of control), is thought to follow and be independent of the affordance problem. In other words, within this framework, the perception of affordances plays a role, but not in the visual guidance of movement.

He then notes that this has been noticed before, and cites Stoffregan (2000):

This separation of the control problem and affordance problem is reinforced by the fact that existing empirical research on affordances emphasizes the role of affordance perception in selecting between modes of action. Stoffregen (2000) pointed out that this has led “to the impression that the primary behavioral utility of affordances is for the selection of behaviors rather than the continuous control of action” (p. 23). He leaves open the possibility that affordances are perceived and exploited in the continuous control of action but acknowledges that the theory of affordances must be developed in a way that the concept can be applied to research on the continuous control of action. This is exactly what the theory of affordance-based control, which is introduced in the following section, is intended to do.

So it seems that, historically, affordances have been treated as solutions to the action selection problem (modes of action, in Warren's terms), but not as solutions to the action control problem, at least until Fajen - and this is why affordance-based control was such a novel move. 

A few things that this link has clarified for me:

  1. Affordances really have (mostly) just been studied in terms of action selection! I actually said this in the throwing/UCM paper, so I apparently knew this, but I don't think I had realised that this was on purpose, rather than just a state of the art question. It's relatively easy to do affordance-for-selection studies; do people try to pass through that aperture or not, for example. But it seems that baked into the Warren work that guides a lot of this is a commitment that affordances are only for action (mode) selection, and not for control, so people do these studies because it's the way to do them. This paper (Barsingerhorn et al, 2012) also discusses this fact.
    1. In fact, I saw Bill at Progress in Motor Control in Rome recently and he explicitly said he still thinks this to me - I didn't quite process it at the time but now it makes sense. So he is still committed to this, and it explains why he thinks Brett is really wrong about affordance-based control. 
    2. Bill also mentioned he thinks Chemero is right about affordances being relations, so apparently that argument is in the mix too. This makes some some sense to me: my connecting affordances to UCM was a natural outcome from my throwing work (specifically Wilson et al, 2016) which is explicitly derived from and committed to affordances-as-dispositional properties of task dynamics, and the connection would never emerge from affordances-as-relations. I was surprised Bill's on Team Chemero here though, I had to admit.
  2. Tom was right, I think, in 2000 that all affordance work was about action selection (although I don't think anyone's looked properly). Since then, however, I know of at least one programme that has looked at affordances in terms of action control; Bingham's reach-to-grasp work I've been reviewing lately. At least some of these papers have explicitly examined movement kinematics with respect to the affordance properties. While I still need to look properly, I suspect this may be it.
    1. This, in part, explains why it never occurred to me not to connect affordances to action control. I've known about Bingham's stuff for years, it was going on in the lab when I was there and Geoff, of course, taught me most of what I know. Geoff is where my affordances-as-properties-of-task-dynamics comes from, as well. What intrigues me know is why Geoff pursued affordances this way but apparently no one else did. 
    2. This issue is also at the heart of my vague discontent with the affordance literature. I've thought for a long time that we haven't been fully walking our talk about affordances, and I had connected that to the fact we aren't doing enough information about affordances research. I know think that all this might be connected to the fact people aren't studying affordances for action control. 
  3. Fajen's affordance-based control is absolutely the right move. I've know this ever since I finally got my head around it, and I've been linking it to my thinking about affordances and UCM from the start. But I also now see much more clearly the context he was working in, and why it was such a radical shift. Understanding the context is a really interesting part of connecting my work to the rest of ecological psychology, so getting clear on this link is important for my thinking. 
What I've learned is that affordances-for-action-control is not as obvious as I thought it was, and neither was Fajen's affordance-based control. I need to get my head much more deeply into Warren's approach because I need to understand the differences, as well. I think affordances for both selection and control is the way to go, but apparently I will have work to do to convince everyone!


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