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

Fixation-related EEG frequency band power analysis: A promising methodology for studying instructional design effects of multimedia learning material

During the last decade the combined recording of eye-tracking data and electroencephalographic (EEG) data has led to the methodology of fixation-related potentials analysis (FRP). This methodology has been increasingly and successfully used to study EEG correlates in the time domain (i.e., event-related potentials, ERPs) of cognitive processing in free viewing situations like text reading or natural scene perception. Basically, fixation-onset serves as time-locking event for epoching and analysing the EEG data. Here, we propose a methodology of fixation-related frequency band power analysis (FRBP) to study cognitive load and affective variations in learners during free viewing situations of multimedia learning materials (i.e., combinations of textual and pictorial elements). The EEG alpha frequency band power at parietal electrodes may serve as a valid measure of cognitive load, whereas the frontal alpha asymmetry may serve as a measure of affective variations. We will briefly introduce and motivate the measures and the methodology, and discuss methodological challenges. The methodology is frontline for learning research, first, as to date the EEG has been seldom used to study design effects of multimedia learning materials and second, as fixation-related EEG data analysis has rarely been done focussing on the frequency domain (i.e., FRBP). Despite methodological challenges still to be solved, FRBP may provide a more in-depth picture of cognitive processing during multimedia learning compared to eye-tracking data or EEG data in isolation and thus may help clarifying effects of multimedia design decisions

Strategies to address gender inequalities in Scottish schools: a review of the literature

This literature review forms the first part of a study of the strategies employed in Scottish schools to address gender inequalities in relation primarily to attainment. In undertaking this task, the intention is to build upon a number of previous investigations into the nature and causes of gender inequalities in schools. Some of these (Riddell, 1996; Osler et al, 2002; Lloyd, 2005) have considered gender and special educational needs; others have discussed gender at particular stages of schooling (Wilkinson et al, 1999; Croxford, 1999; Biggart, 2000); whilst a number of recent projects in the UK and in Scotland (Powney, 1996; Sukhnandan, 1999; Tinklin et al, 2001) have considered gender, attainment and/or achievement across the population and span of compulsory schooling. A recent nationally commissioned report (Younger, Warrington et al, 2005) has specifically investigated the issue of raising the attainment of boys. Together, these studies and others have established that there are gender inequalities both in the forms of participation in schooling and in its outcomes (albeit there is agreement that gender is not the only, nor even the main, source of inequality). Also available from this body of literature are analyses of causes of gender inequalities and debate about the strategies schools might adopt to address these inequalities. These strategies arise, in general, from understandings of the nature and causes of gender difference. There is, therefore, some contention here. A number of commentators argue that some of the strategies adopted by schools pathologise gender differences and hence reinforce particular forms of masculinity at the risk of suppressing, or marginalising, other forms, and at the expense of femininities. Evidence that there are gender inequalities in attainment in Scottish schools has been discussed in detail elsewhere. It will be reviewed briefly here and will be related to broader patterns of inequality, and in particular to social class. For this study, though, with its focus on school strategies, the debate about the causes of gendered outcomes is especially important and it will be treated in some depth and related to social class before the discussion moves on to consider the range of strategies employed in schools, as far as they are represented in the literature. The strategies to be considered encompass approaches to learning, teaching and assessment; aspects of classroom organisation; and school-wide issues such as staff development. All of these will be considered critically in the light of previous discussion of the causes of gender differences and their intersection by other, and arguably more influential, forms of identity

Access to Elementary Education in India

This analytical review aims to explore trends in educational access and to delineate different groups which are vulnerable to exclusion from educational opportunities at the elementary stage. This review has drawn references from a series of analytical papers developed on different themes, including regional disparity in education, social equity and gender equity in education, the problem of drop out, education of the children of migrants, inequity in educational opportunities, health and nutrition, and governance of education, among others. The first and second sections of the paper present a brief review of the state of elementary education in India with particular focus on regional disparities and social inequities in provision. The third section delineates different zones of exclusion, highlighting the nature and magnitude of the problems of access, transition and equity. The fourth section captures the profiles of the varying groups of children and addresses the questions: ‘who is excluded from schooling?’ and ‘why are they excluded?’. In the final section, the paper makes an effort to identify gaps in our understanding which point to the need for further research and also identifies strategies that have had some success in addressing issues of access to elementary education in India