Documents 

The primary goal of this dissertation was to understand to what extent are humans capable of accurately perceiving both their own rotations and the rotations of others and how do spatial manipulations of the actor and the perceiver affect the perception of the action. Four experiments were conducted. Experiment 1 examined the perceptual abilities of both expert gymnasts and novices in the accurate judgment of either a left or right rotation by an animated human figure (avatar) in a series of fixed picture plane orientations. Participants responded with either a verbal “left” or “right” and their mean accuracy and mean response time were recorded. Experiment 2 used the same stimulus but the participants were asked to report their answers by way of one of four arrow button combinations; right button corresponded to a right twist, left button corresponded to a right twist, up button corresponded to a right twist and down button corresponded to a right twist. Both mean accuracy and response time were recorded for each group. Experiment 3 mirrored Experiment 1 except the participants were randomly fixed in one of six picture plane orientations from 0° to 300° of rotation. Experiment 4 used the same apparatus as Experiment 3 where the participants were randomly placed in one of six picture plane orientations however the participants were rotated either left or right and were asked to verbally report their own twisting direction. Experiment 4 tested both novices and expert gymnasts. The general results suggest that the task of accurately determining the twisting direction of another human form is challenging and cognitively demanding. Under most conditions accuracy decreased and response time increased as the phase angle between the participant and the avatar approached 180°. In Experiment 1 experts and novices performed the same and were least accurate and took the longest to respond when the avatar was inverted. The results from Experiment 2 suggested a conflict of strategies between the constraints of the task and the inherent challenge of the task. Participants in Experiment 3 were generally uninfluenced by their own picture plane orientation and in almost all combinations of participant and avatar picture plane orientation they were more accurate and faster than the exclusively upright participants in
Experiment 1. The experts in Experiment 4 were flawless in their responses and significantly faster than in any other experiment. The novices were also relatively fast but the accuracy of the judgments on their own twisting directions was no better than the participants watching the avatar in Experiment 1. The findings suggest that the general task of determining human rotation as either a left or right turn is so challenging that a number of conflicting strategies may have been employed by the participants to help lessen the cognitive demands of the task. The data speaks to the specificity of expertise and outlines a potential discrepancy between expert observers and expert performers. The data suggests that the use of an internal reference frame during the spatial perception of biological motion may be consistent across conditions regardless of participant orientation. [editor summary]

Two lines of research on the related skills of rhythmic bouncing a ball and juggling three balls were reviewed with the goal to reveal commonalities in the strategy typifying the dynamic systems approach to movement coordination. For both lines of research concepts from nonlinear dynamics and their experimental results were presented in parallel. While there were evident differences in the physical principles and key variables, the dual presentation demonstrated the similarity in the modeling strategy and the methodology. Criteria for dynamically stable solutions defined the boundaries that the actor's movements had to satisfy in order to perform the rhythmic task. Essential in both approaches was that one key variable provided the reference frame for evaluating skilled performance and the process of learning. The role of perceptual information was evaluated by the decrement in stability of performance that selected perceptual manipulations induced. Individual differences between subjects in ball bouncing were shown to be the consequence of their choice of the key variable, which further constrained the kinematic properties across different movement realizations. Individual differences between expert jugglers were interpreted as their "deliberate" choice of a solution that was not tightly constrained by maximum stability but rather one that afforded them more flexibility. This contrasting review aimed to show the spectrum of tools that a dynamic approach has to offer. It further showed that an analysis from a nonlinear dynamic perspective can establish a basis from which a set of important issues in motor control can be addressed, in a quantitative and physically principled manner. [author summary]

This paper presents the training of juggling skills, a highly complex problem of coordination, under tight time and space constraints. This training is achieved with a simple training platform, a light weight juggling platform (LWJ), and is compared to training with real balls. The principle directing the design of the platform is to obtain a simple tool. The simplification, in comparison to real world juggling, is based on the identification of invariant properties in the spatiotemporal coordination of intermediate and expert jugglers. Two classes training solutions were added to the LWJ: An audio-tactile pacing or augmented multimodal environment, and the manipulation of cognitive components of the juggling skills. The transfer to juggling with real balls was evaluated in four different experiments. [authors summary]