Lissajous feedback and coordination stability

Understanding the perceptual information you provide people in a task is a critical element of the perception-action analysis. Last time I talked about the new form of coordination feedback I developed to allow us to train coordinated rhythmic movements without perturbing the task dynamic. Prior to this, the most common form of augmented feedback was the Lissajous plot - these are the result of plotting the displacements of two harmonic oscillators against one another, and the unique shape associated with each relative phase can be used as a template on the screen. People can then try to move so as to make a dot trace that shape.

Lissajous plots (have a play with them in this Excel file) are transformed feedback, because they take a coordinated movement and represent it on the screen as the motion of a single dot. This type of feedback has been used extensively to train people to perform novel coordinations, but until recently no-one had thought to investigate the consequences of transforming the information about relative phase. Kovacs, Buchanan and Shea have recently begun doing exactly this, and, in line with the perception-action approach developed by Bingham and pushed at every opportunity by myself, these authors have found that Lissajous plots completely alter the nature of the task, with serious consequences for the studies that rely on it.

Visual feedback for training novel coordinations

The key feature of coordinated rhythmic movements is that not all coordinations are stable. Most other rhythms can be learned, however, which is why we can have jazz drumming. People have been training participants to perform novel coordinations (especially 90°, the least stable rhythm without training) for years now, and have been asking all the standard learning questions - how long does learning take? Does it transfer to other coordinations? 

The first real studies on learning were by Kelso and Zanone (Kelso & Zanone, 2002; Zanone & Kelso, 1992a, b, 1997). I briefly reviewed the results of these studies here, which have lead to to the dynamic pattern hypothesis. This account describes stable states as attractors in a state space defined by relative phase as the order parameter, and learning is the creation of a new attractor centred on the target novel phase. This account ran into problems quite quickly but is still alive and kicking in a modified form; stability is the governing principle now, and from this perspective the feedback displays used for training don't matter so long as they support stable action. 

However, from our perception-action standpoint, the feedback displays matter a lot, because these are what's providing the perceptual information about the coordinated movement. Early learning studies all used some kind of transformed feedback, which we could never use because it altered the overall perception-action dynamic. In order to look at action learning directly, we needed a new form of feedback. 

So I invented one.