The Perturbation Experiment as a Way to Study Perception

When you study perception, your goal is to control the flow of information going into the system so that you can measure the resulting behaviour and evaluate how that information is being used. There are two ways to do this, one (sometimes) used by me, one used by, well, everyone else. In this post I'm going to compare and contrast the methods and describe why the perturbation method is what we should all be doing.

The standard method is to present experimentally isolated cues and test whether people can detect those cues. The perturbation experiment presents a 'full cue' environment but selectively interferes with the link between a single variable and the property it might be information about. These two different methods lead to very different ways of thinking and talking about perceptual abilities. 

Perception, Action & Dynamical Systems

Over Easter I visited the Center of Functionally Integrative Neuroscience at Aarhus University in Denmark, courtesy of the Interacting Minds group. I gave a talk, got the tour, and met some of the faculty and students - some interesting opportunities for future collaborations, I hope - thanks for the hospitality!

I wanted to lay out the basics of the talk I gave. I took the opportunity to present some ideas that have been developing as I work on this blog, reading Chemero and working on coordination experiments. There is a core of people in Aarhus interested in things ecological, as well as dynamical systems, so it was a good audience to try these ideas out and they seemed to go over well. This is also the sketch of a paper Sabrina and I are going to work on over the summer.

The take home message of the talk was simple - dynamical systems is the right kind of mindset for cognitive science, but it is not a theory of behaviour. Dynamics merely provides the right kind of modelling tools - the form of the model must be based on hypotheses about the specific kind of dynamical systems we are or else they are merely an exercise in data-fitting. Ecological psychology is the right theory, and the Bingham model of coordinated rhythmic movement is currently the only example of a genuinely perception-action dynamical systems model. My thoughts here are largely from my response to Chapter 4 of Chemero (on 'the dynamical stance') and Chapter 5, his initial attempt to use dynamics to serve as a guide to discovery which I think fails and which Chemero then replaces with ecological psychology. The description of Bingham's model comes from here.

Identifying the Visual Information for Relative Phase

Bingham's model predicts that the information for relative phase is the relative direction of movement. The first direct test of this hypothesis was the experiment that followed on from my learning study, in which we systematically perturbed the various candidate information variables to see which affected performance in the perceptual judgement task.

I like this study a lot, if I do say so myself. It's a serious attempt to make a strong test of the model's predictions, and we invested a lot of time in the methodology. This is also that rare paper that benefited from a vigorous review process; the end result is, I think, a clear, careful, and detailed presentation of a critical result for the perception-action approach Geoff and I are developing.

Readers interested in the issue of how you can scientifically study information from an ecological perspective should certainly read the paper (Ken, that's you :); it's my go-to reference for how I believe this has to be done. The main lesson - it's hard to do this properly, but the rewards, in terms of unambiguous data, are clear.

A Perception/Action Model of Coordination

Other coordination posts are here.

The role of perception in the dynamic leading to the HKB phenomena has been made clear by the work so far. But the exact form of this dynamic had yet to be modelled; the HKB model only consists of two cosine functions superimposed on each other to produce the two attractors at 0° and 180°, and the dynamic pattern hypothesis it embodies made predictions which did not held up empirically. It was now time to take an explicitly perception/action approach to modelling the task, which means it's finally time to turn to (my PhD advisor) Geoff Bingham's model (2001, 2004a, 2004b). This model is a fully perception/action model, and the modelling strategy Bingham lays out is, I think, a masterclass in how to go about building models of this kind.