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.