Thomas W. Calvert

Moticons: detection, distraction and task

In this paper, we describe an empirical investigation of the utility of several perceptual properties of motion in information-dense displays applied to notification. Notification relates to awareness and how dynamic information is communicated from the system to the user. Key to a notification technique is how easily the notification is detected and identified. Our initial studies show that icons with simple motions, termed moticons, are effective coding techniques for notification and in fact are often better detected and identified than colour and shape codes, especially in the periphery. A subsequent experiment compared the detection and distraction effects of different motion types in several task conditions. Our resutts reveal how different attributes of motion contribute to detection, identification and distraction and provide initial guidelines on how motion codes can be designed to support awareness in information-rich interfaces while minimizing unwanted side effects of distraction and irritation.

A Systems Model of the Effects of Training on Physical Performance

A systems model is proposed to relate a profile of athletic performance to a profile of training. The general model assumes that performance has four components: endurance, strength, skill, and psychological factors. Each of these factors is discussed and ascribed a transfer function. A major problem is the quantification of both training and performance. The case of a swimmer is studied in detail. It is shown that if a time series of training impulses is used as input, his performance in 100 m criterion performances can be modeled rather well with a simple linear system. The major conclusion is that performance appears to be related to the difference between fitness and fatigue functions. The fitness function is related to training by a first-order system with time constant 50 days, whereas the fatigue function is related to training by a similar system with time constant 15 days. An appendix is provided to show how these systems can be simulated on a simple electronic calculator. The relationship of these relatively short-term efects on the individual performer (six months) to longer term effects on the same indiviudal is also discussed.

MECHANICAL RESONANCE OF THE HUMAN BODY DURING VOLUNTARY OSCILLATIONS ABOUT THE ANKLE JOINT

Viscoelastic models of the musculoskeletal system suggest resonant frequencies of oscillatory movement at which maximal output is realized with minimal energy expenditure. To investigate this, resonance at the human ankle joint was explored by comparing predicted and experimental gain/frequency and phase frequency functions. These functions were predicted from viscous (B) and elastic (K) coefficients of ankle extensors which were determined from the damped sinusoidal force produced after landing with muscles in sustained contraction (B = 3986 kg/s, K = 31,898 kg/s2). Experimental input/output functions were determined from Fourier analysis of force (output) and rectified, filtered EMG (input) obtained during voluntary sinusoidal oscillations of ground reaction force of a specified magnitude and frequency. Correlations between predicted and experimental functions were significant (p less than 0.02) in four of five subjects. The average resonant frequency was 3.33 +/- 0.15 Hz. The mechanical properties of muscle are considered to be as important as the nervous system in determining the choice of both the movement pattern and the strategy which is adopted in response to changing conditions.

Deriving spectra from colors and rendering light interference

A new method for transforming colors into spectra, which we applied to rendering light interference using a standard ray tracer, significantly enhances color-based rendering software and graphics platforms.

The relationship between the surface EMG and force transients in muscle: Simulation and experimental studies

The surface electromyogrmn (EMG) is an easily measured signal which when quantified by present techniques is a reliable measure of whether a muscle is active, a fairly reliable measure of steady state force and a rather unreliable measure of force transients in muscle. There is a real need for a reliable indicator of dynamic changes in muscle activity for the control of prosthetics, in diagnosis of neuromuscular diseases, in studies of the motor control system and in fundamental studies of muscle mechanics. This paper outlines the principles underlying the development of force and the EMG in muscle. The EMG is a poor estimate of muscle force since it is the result of the linear superposition of biphasic action potentials which result in an interference pattern. This in turn is dependent on the details of the firing intervals for each motor unit, whereas the force is quite insensitive to these details. Experimental results for the human biceps brachii are described in which it was not possible to obtain a consistent estimate of muscle active state from the EMG. An extensive computer simulation was used to explore the relationship between EMG and force under a variety of assumptions. The conclusion is that it is technically impossible to obtain consistent estimates of muscle force (or active state) unless a filter with a time constant of 300 ms is applied to the rectified EMG. This is inconsistent with the estimation of active state for voluntary contractions with observed rise time constants of 30-70 ms. It is susgested that the only solution is to repeat an experiment many times and average the rectified EMG. Unfortunately, in practice it is difficult to repeat certain aspects of voluntary muscular contractions.

Rendering Iridescent Colors of Optical Disks

Iridescent colors of optical disks are caused by light diffraction from their surface microstructure. This paper proposes a diffractive illumination model for optical disks based on their physical structure and the superposition principle of light waves. This model includes contributions due to diffractive and non-diffractive factors. For the diffractive part, we first model the pit periodicity for optical disks by using identical spheres and then simplify their distribution by uniform groups of spheres. We also propose and prove the condition for highlights on illuminated grooved surfaces; this condition provides the non-diffractive contribution. The rendered images using this model achieve excellent agreement with photographs of real optical disks.

Composition of multiple figure sequences for dance and animation

Insights gained from an interdisciplinary study of the creative processes involved in dance composition are the basis for developing computer-based tools to support dance composition and animation. The system that has been developed, Life Forms, provides an interactive hierarchical environment where the user can reduce the complexity of the task by flexibly switching between spatial and temporal views of the composition. Realistic animation of the final result is also available. Life Forms, which is implemented on IRIS and Macintosh workstations, has proven itself to be of real value in dance composition. It is now being tested as the front end of a conventional animation system for use in animating multiple articulated figures.

The evolution of an interface for choreographers

This paper describes the evolution of the interface to Life Forms, a compositional tool for the creation of dance choreography, and highlights some of the important lessons we have learned during a six year design and implementation period. The lessons learned can be grouped into two categories: 1) Process, and 2) Architecture of the Interface. Our goal in developing a tool for choreography has been to provide computer-based creative design support for the conception and development of dance. The evolution was driven by feedback from the choreographers and users who were members of the development team, combined with our knowledge of current thinking on design and composition. Although the interface evolved in a relatively unconstrained way, the resulting system has many of the features that theoretical discussion in human interface design has projected necessary. The Life Forms interface has evolved incrementally with one major discontinuity where adoption of a new compositional primitive required a completely new version.

The integration of subjective and objective data in the animation of human movement

Animation of human movement can be based either on analog inputs derived directly from actual movements or on symbolic inputs chosen to produce the desired movement. The former type of input can be quite accurate and objective but is a description of the required movement whereas the latter is often quite imprecise and subjective but provides an analysis of the required movements. Two existing systems for a computer based animation are being used to explore the problems involved in integrating such inputs. Specifically, animation driven by analog signals from electro-goniometers is integrated with animation derived from Labanotation commands; the results are illustrated with a short movie.

Tools for interaction with the creative process of composition

This paper explores the nature of creative composition particularly as it applies to dance, and describes the development of interactive computer based tools to assist the composer. The hierarchical nature of the composition process calls for an interface which allows the composer the flexibility to move back and forth between alternate views and conceptual levels of abstraction. COMPOSE, an interactive system for the composition of dance has been implemented on Silicon Graphics and Apple workstations. The user visually composes in space and in time using menus of postures and sequences. Paths can be edited and an animation of the dance composition allows the final result to be evaluated.