Thesis (PhD) - Indiana University, Psychology, 2005
Coordinated rhythmic movement is very specifically structured in humans. 0° mean relative phase (the two oscillating limbs doing the same thing at the same time) is easy and stable; 180° (the two limbs doing the opposite thing at the same time) is less stable; and no other relative phase is stable without training. The present study explored the identity and role of the perceptual information used in rhythmic movement coordination tasks in creating this pattern. 4 participants were trained to improve their perceptual resolution of 90° over a two week period. This training resulted in improved movement stability in a rhythmic movement coordination task, without additional practice of the task itself. Improved ability to detect the information at 90° allowed for improved performance in a movement task at 90°. In a second study, we systematically perturbed three aspects of the coordinated motion of two dots on a computer screen, and tested the effect of these perturbations on the same 4 participants. In line with predictions based on previous modeling results, perturbations that disrupted perceptual information about peak velocity and peak amplitude disrupted participants' ability to perform the task; this information allows rescaling of velocity information and is vital for stable perception of the underlying information (the relative direction of motion). Perturbations that increased the magnitude of the relative speed between the dots added noise to the task, again as predicted. Relative direction proved impossible to perturb, independently of mean relative phase, suggesting it has a vital role in the task. We conclude that the information used in rhythmic movement coordination tasks is both the phase (position within a cycle) and the relative phase, instantiated as the relative direction of motion. Movement stability is a function of perceptual stability, and improving the latter improves the former. The results are explained within a perception-action framework, in which perceptual information is an integral part of the organization of a perception-action dynamical system.