Characterisation of nystagmus waveforms in eye-tracker signals

This thesis deals with the analysis of eye–tracker signals recorded from nystagmus patients. Nystagmus is an eye movement disorder caused by an underlying condition, and patients who suffer from nystagmus express involuntary oscillating eye move- ments. The oscillatory patterns expressed by these patiens are typically linked to the underlying condition, but it is usually difficult to precisely diagnose each individual. The main focus of this thesis is to develop methods for automatic and robust analysis of nystagmus eye movements. These methods are developed with the purpose of providing diagnostic support for clinicians, or for evaluation of treatment effects.This thesis comprises an introduction and four papers describing various aspects of nystagmus analysis. In all four papers, eye movement signals recorded using an eye tracker are used as input to the proposed methods. In the first paper, a method to robustly calibrate eye–tracker data recorded from nystagmus patients is proposed. Calibration of data from nystagmus patients using video–based systems is difficult since the calibration process relies on an ability to accurately and precisely fixate calibration targets, which is difficult for nystagmus patients. Due to the nystagmus oscillations, it is difficult to obtain calibration results that are acceptable in terms of accuracy. In this work, a novel approach to find outliers in the calibration data is implemented, and a linear Procrustes transformation is used as the calibration mapping function. The results show that the proposed approach leads to reduced gaze estimation variance, and a higher robustness against outliers in the calibration data.In the second paper, a method to model different nystagmus waveform morphologies is presented. This model is used to characterise the nystagmus oscillations and to assert the quality of the analysed eye–tracker signals. The modelling approach is based on a stationary harmonic series, and the signals are modeled in short seg- ments, allowing for tracking of local changes in signal characteristics. Each segment is assessed using a metric referred to as the normalised segment error, which is used to determine whether or not the segment contains measurement disturbances. The results show that the model is well suited to distinguish between nystagmus oscillations and disturbances in the signal.The harmonic model from the second paper is used in the third paper in order to analyse data acquired during both smooth pursuit and fixation eye movements. Smooth pursuit eye movements may carry valuable clinical information, and reliable modelling of smooth pursuit eye movements is therefore of interest. The harmonic model is used to parametrise the different waveforms. Based on the parametrisation, a waveform distance index is defined, which is a metric used to measure similarity between waveforms, as well as for clustering of waveforms. Eleven different clusters are defined using known reference nystagmus waveforms, and all recorded fixation and smooth pursuit waveforms are assigned to one of the eleven cluster centers. The results show that the waveform clustering is robust, is able to distinguish between recordings from different individuals, and is suitable for analysis of smooth pursuit recordings.In the fourth paper, a novel method to combine cycle analysis and morphological classification is proposed. The goal of this work is to provide a diagnostic tool to identify subtle differences between patients, and over time in longer or recurring recordings. The cycle analysis method uses adaptive thresholds in order to detect breaking saccades, fast phases, foveations and slow phases. Eighteen template waveforms are used to create a profile of identified morphologies for each recorded waveform. The method is evaluated against expert annotations from a public dataset. The results show that the method is capable of analysing nystagmus eye movement recordings from both video–based and magnetic scleral search coil techniques. The waveform classification is reliable for both recording techniques.The methods presented in this thesis are used to improve the robustness and reliability for analysis of nystagmus eye movements recorded using an eye–tracker. In total, the four proposed methods constitute a complete framework showing how analysis of nystagmus eye–tracker signals may be used to improve diagnostics in nystagmus patients

Eye tracking: empirical foundations for a minimal reporting guideline

In this paper, we present a review of how the various aspects of any study using an eye tracker (such as the instrument, methodology, environment, participant, etc.) affect the quality of the recorded eye-tracking data and the obtained eye-movement and gaze measures. We take this review to represent the empirical foundation for reporting guidelines of any study involving an eye tracker. We compare this empirical foundation to five existing reporting guidelines and to a database of 207 published eye-tracking studies. We find that reporting guidelines vary substantially and do not match with actual reporting practices. We end by deriving a minimal, flexible reporting guideline based on empirical research (Section "empirically based minimal reporting guideline")

Development of a feedback-controlled elbow simulator: design validation and clinical application

This work involves three topics that advance the functionality of an elbow simulator in the Orthopaedic Biomechanics Laboratory at Allegheny General Hospital. To draw clinically and scientifically meaningful conclusions from future cadaver studies conducted with the simulator, its design must be validated and the accuracy of the data collection methods demonstrated. The simulator was designed to offer physiologically-correct adjustable moment arms throughout the elbow's range of motion. To validate this, muscle moment arms were measured in three cadaver elbow specimens. Flexion-extension moment arms were measured at three different pronation/supination angles: fully pronated, fully supinated, and neutral. Pronation-supination moment arms for four elbow muscles were measured at three different flexion-extension angles: 30°, 60°, and 90°. The numeric results compared well with those previously reported. The biceps and pronator teres flexion-extension moment arms varied with pronation-supination position, and vice versa. This represents the first use of closed-loop feedback control in an elbow simulator, one of the first reports of both flexion-extension and pronation-supination moment arms in the same specimens, and demonstrates the adjustability of the moment arms that the elbow simulator can produce.Towards accurate motion analysis of the radial head, two areas were investigated. The first identified the phenomena of camera-switching, which occurs in motion analysis when data from one or more cameras is temporarily excluded from the computation of a marker's three-dimensional position. Tests with static markers showed that camera-switching could cause up to 3.7 mm of perceived movement. The second area of investigation set the stage for future studies with cadaver elbows. A protocol was developed to quantify both the travel of the native radial head, radial head implants, and the finite helical axis during pronation-supination movement. The tracking of implant motion employs a unique circle-fitting algorithm to determine the implant's center. A video-based motion analysis system was used to collect marker position coordinates actuated by a precision micrometer table. MATLAB code was designed and implemented to compute both the radial head position and finite helical axis from these data. Immediate future work will use these algorithms to evaluate radial head implants in comparison to the native radial head

Dynamic simulation and control of optical systems

This thesis deals with the simulation-based investigation and control of optical systems that are mechanically influenced. Here, the focus is on the dynamic-optical modeling of vibration-sensitive mirror systems, which are utilized, e.g., in large astronomy telescopes or high-precision lithography optics. The large-area primary mirrors of telescopes typically consist of many individual hexagonal mirror segments, which are positioned with precise sensors and actuators. Furthermore, an adaptive optical unit usually compensates for the optical aberrations due to atmospheric disturbances. In practice, these aberrations are detected, and corrected, within a few seconds using deformable mirrors. However, to further improve the performance of these optical systems, dynamical disturbances in the mechanics, i.e., small movements and deformations of the optical surfaces, must also be taken into account. Therefore, multidisciplinary simulation methods are developed and presented. Based on this, the dynamical-optical system behavior is modeled using model-order-reduced, flexible multibody systems. Hence, the dynamical analysis of the mechanical-optical system can be performed at low computation costs. Thanks to the optical analysis in the time domain and using Fourier-optical concepts, one can also simulate exposure processes. To actively compensate for aberrations due to mechanical vibrations, model-based control strategies are also designed. They are not only demonstrated by means of simulation examples, but also illustrated through a laboratory experiment. The latter is realized with a low-cost test setup for student training using Arduino microcontrollers, position and force sensors, as well as high-speed cameras

EG-ICE 2021 Workshop on Intelligent Computing in Engineering

The 28th EG-ICE International Workshop 2021 brings together international experts working at the interface between advanced computing and modern engineering challenges. Many engineering tasks require open-world resolutions to support multi-actor collaboration, coping with approximate models, providing effective engineer-computer interaction, search in multi-dimensional solution spaces, accommodating uncertainty, including specialist domain knowledge, performing sensor-data interpretation and dealing with incomplete knowledge. While results from computer science provide much initial support for resolution, adaptation is unavoidable and most importantly, feedback from addressing engineering challenges drives fundamental computer-science research. Competence and knowledge transfer goes both ways