Ian Stavness

A dynamic model of jaw and hyoid biomechanics during chewing

Our understanding of human jaw biomechanics has been enhanced by computational modelling, but comparatively few studies have addressed the dynamics of chewing. Consequently, ambiguities remain regarding predicted jaw-gapes and forces on the mandibular condyles. Here, we used a new platform to simulate unilateral chewing. The model, based on a previous study, included curvilinear articular guidance, a mobile hyoid apparatus, and a compressible food bolus. Muscles were represented by Hill-type actuators with drive profiles tuned to produce target jaw and hyoid movements. The cycle duration was 732 ms. At maximum gape, the lower incisor-point was 20.1mm down, 5.8mm posterior, and 2.3mm lateral to its initial, tooth-contact position. Its maximum laterodeviation to the working-side during closing was 6.1mm, at which time the bolus was struck. The hyoids movement, completed by the end of jaw-opening, was 3.4mm upward and 1.6mm forward. The mandibular condyles moved asymmetrically. Their compressive loads were low during opening, slightly higher on the working-side at bolus-collapse, and highest bilaterally when the teeth contacted. The models movements and the directions of its condylar forces were consistent with experimental observations, resolving seeming discordances in previous simulations. Its inclusion of hyoid dynamics is a step towards modelling mastication.

ArtiSynth: A Fast Interactive Biomechanical Modeling Toolkit Combining Multibody and Finite Element Simulation

ArtiSynth (http://www.artisynth.org) is an open source, Java-based biomechanical simulation environment for modeling complex anatomical systems composed of both rigid and deformable structures. Models can be built from a rich set of components, including particles, rigid bodies, finite elements with both linear and nonlinear materials, point-to-point muscles, and various bilateral and unilateral constraints including contact. A state-of-the-art physics simulator provides forward simulation capabilities that combine multibody and finite element models. Inverse simulation capabilities allow the computation of the muscle activations needed to achieve prescribed target motions. ArtiSynth is highly interactive, with component parameters and state variables exposed as properties that can be interactively read and adjusted as the simulation proceeds. Streams of input and output data, used for controlling or observing the simulation, can be viewed, arranged, and edited on an interactive timeline display, and support is provided for the graphical editing of model structures.

pCubee: a perspective-corrected handheld cubic display

In this paper, we describe the design of a personal cubic display that offers novel interaction techniques for static and dynamic 3D content. We extended one-screen Fish Tank VR by arranging five small LCD panels into a box shape that is light and compact enough to be handheld. The display uses head-coupled perspective rendering and a real-time physics simulation engine to establish an interaction metaphor of having real objects inside a physical box that a user can hold and manipulate. We evaluated our prototype as a visualization tool and as an input device by comparing it with a conventional LCD display and mouse for a 3D tree-tracing task. We found that bimanual interaction with pCubee and a mouse offered the best performance and was most preferred by users. pCubee has potential in 3D visualization and interactive applications such as games, storytelling and education, as well as viewing 3D maps, medical and architectural data.

Automatic prediction of tongue muscle activations using a finite element model

Computational modeling has improved our understanding of how muscle forces are coordinated to generate movement in musculoskeletal systems. Muscular-hydrostat systems, such as the human tongue, involve very different biomechanics than musculoskeletal systems, and modeling efforts to date have been limited by the high computational complexity of representing continuum-mechanics. In this study, we developed a computationally efficient tracking-based algorithm for prediction of muscle activations during dynamic 3D finite element simulations. The formulation uses a local quadratic-programming problem at each simulation time-step to find a set of muscle activations that generated target deformations and movements in finite element muscular-hydrostat models. We applied the technique to a 3D finite element tongue model for protrusive and bending movements. Predicted muscle activations were consistent with experimental recordings of tongue strain and electromyography. Upward tongue bending was achieved by recruitment of the superior longitudinal sheath muscle, which is consistent with muscular-hydrostat theory. Lateral tongue bending, however, required recruitment of contralateral transverse and vertical muscles in addition to the ipsilateral margins of the superior longitudinal muscle, which is a new proposition for tongue muscle coordination. Our simulation framework provides a new computational tool for systematic analysis of muscle forces in continuum-mechanics models that is complementary to experimental data and shows promise for eliciting a deeper understanding of human tongue function.

The MUSICtable: a map-based ubiquitous system for social interaction with a digital music collection

Popular acceptance of the mp3 digital music standard has greatly increased the complexity of organizing and playing large music collections. Existing digital music systems do not adequately support exploration of a collection, nor do they cater to multi-user interaction in a social setting. In this paper, we present the design of a ubiquitous system that utilizes spatial visualization to support exploration and social interaction with a large music collection. Our interface is based on the interaction semantic of influence, which allows users to affect and control the mood of music being played without the need to select a set of specific songs. This design is inspired, to some extent, by Gaver’s work on ludic design. We implemented a prototype as a proof of concept of our design. User testing demonstrates that our system encourages participation and strengthens social cohesion. Our work contributes to interactive interface research in that it extends the utility of map-based visualization of digital music.

Deep Plant Phenomics: A Deep Learning Platform for Complex Plant Phenotyping Tasks

Plant phenomics has received increasing interest in recent years in an attempt to bridge the genotype-to-phenotype knowledge gap. There is a need for expanded high-throughput phenotyping capabilities to keep up with an increasing amount of data from high-dimensional imaging sensors and the desire to measure more complex phenotypic traits (Knecht et al., 2016). In this paper, we introduce an open-source deep learning tool called Deep Plant Phenomics. This tool provides pre-trained neural networks for several common plant phenotyping tasks, as well as an easy platform that can be used by plant scientists to train models for their own phenotyping applications. We report performance results on three plant phenotyping benchmarks from the literature, including state of the art performance on leaf counting, as well as the first published results for the mutant classification and age regression tasks for Arabidopsis thaliana.

Predicting muscle patterns for hemimandibulectomy models

Deficits in movement and bite force are common in patients following segmental resection of the mandible consequent to oral cancer or injury. We have previously developed a dynamic model to analyse the biomechanics of an ungrafted segmental jaw resection with unilateral muscle and joint loss and post-surgical scarring. Here, we describe an inverse-modelling algorithm for automatically predicting muscle activations in the model for prescribed jaw movement and bite-force production. We present the results of simulations that postulate combined muscle activation patterns that could theoretically be used by patients to overcome post-surgical deficits. Such predictions could be the basis for future muscle retraining in clinical cases.

Biomechanical modeling of English /r/ variants

This study reports an investigation of the well-known context-dependent variation in English /r/ using a biomechanical tongue-jaw-hyoid model. The simulation results show that preferred /r/ variants require less volume displacement, relative strain, and relative muscle stress than variants that are not preferred. This study also uncovers a previously unknown mechanism in tongue biomechanics for /r/ production: Torque in the sagittal plane about the mental spine. This torque enables raising of the tongue anterior for retroflexed [Symbol: see text] by activation of hyoglossus and relaxation of anterior genioglossus. The results provide a deeper understanding of the articulatory factors that govern contextual phonetic variation.

A comparison of simulated jaw dynamics in models of segmental mandibular resection versus resection with alloplastic reconstruction.

STATEMENT OF PROBLEM Composite mandibular resection resulting in mandibular discontinuity can alter jaw motion, occlusal forces, and mastication, whether or not the jaw is reconstructed. The biomechanical events associated with these changes are difficult to assess clinically and, therefore, are not well documented or researched. PURPOSE The purpose of this study was to model movements of a mandible with a discontinuity defect, and to compare them to movements of a mandible with its continuity restored by alloplastic reconstruction. MATERIAL AND METHODS Computational models were created with a novel simulation platform. The variables designed into the models included gravity, external forces, and jaw muscle activity. Each jaw was observed at rest, when opened by external force or by muscle drive, and during the generation of unilateral occlusal force on the nonoperated side. Scarring was simulated with springlike forces. Outputs included individual muscle forces and torques, as well as mandibular incisor and condylar motions. RESULTS Both models displayed plausible resting postures, and jaw opening with deviation toward the defect side when scarring was simulated. Opening caused by downward force on the incisors differed from that due to muscle activation. Jaw rotations during unilateral molar contact on the unaffected side were muscle specific and influenced by mandibular discontinuity. CONCLUSIONS Plausible jaw movements after hemimandibulectomy and/or alloplastic reconstruction could be predicted by dynamic modeling. The effect of soft tissue forces on jaw posture and movements varied with the condylar support available. In both models, different opening trajectories were produced by external force on the jaw and by jaw muscle activation. Mandibular rotation during unilateral molar contact depended on which muscles were activated, and the availability of bilateral condylar support.

Quantifying and Mitigating the Negative Effects of Local Latencies on Aiming in 3D Shooter Games

Real-time games such as first-person shooters (FPS) are sensitive to even small amounts of lag. The effects of net-work latency have been studied, but less is known about local latency, the lag caused by input devices and displays. While local latency is important to gamers, we do not know how it affects aiming performance and whether we can reduce its negative effects. To explore these issues, we tested local latency in a variety of real-world gaming scenarios and carried out a controlled study focusing on targeting and tracking activities in an FPS game with varying degrees of local latency. In addition, we tested the ability of a lag compensation technique (based on aim assistance) to mitigate the negative effects. Our study found local latencies in the real-world range from 23 to 243 ms which cause significant and substantial degradation in performance (even for latencies as low as 41 ms). The study also showed that our compensation technique worked extremely well, reducing the problems caused by lag in the case of targeting, and removing the problem altogether in the case of tracking. Our work shows that local latency is a real and substantial problem -- but games can mitigate the problem with appropriate compensation methods.