Variability analysis of discrete event series and wavefront patterns in surface electrocardiogram: contributions to psychophysiological and clinical research

The surface electrocardiogram (ECG) is an established diagnostic tool for the detection of abnormalities in the electrical activity of the heart. The interest of the ECG, however, extends beyond the diagnostic purpose. In recent years, studies in cognitive psychophysiology have related heart rate variability (HRV) to memory performance and mental workload. The aim of this thesis was to analyze the variability of surface ECG derived rhythms, at two different time scales: the discrete-event time scale, typical of beat-related features (Objective I), and the “continuous” time scale of separated sources in the ECG (Objective II), in selected scenarios relevant to psychophysiological and clinical research, respectively. Objective I) Joint time-frequency and non-linear analysis of HRV was carried out, with the goal of assessing psychophysiological workload (PPW) in response to working memory engaging tasks. Results from fourteen healthy young subjects suggest the potential use of the proposed indices in discriminating PPW levels in response to varying memory-search task difficulty. Objective II) A novel source-cancellation method based on morphology clustering was proposed for the estimation of the atrial wavefront in atrial fibrillation (AF) from body surface potential maps. Strong direct correlation between spectral concentration (SC) of atrial wavefront and temporal variability of the spectral distribution was shown in persistent AF patients, suggesting that with higher SC, shorter observation time is required to collect spectral distribution, from which the fibrillatory rate is estimated. This could be time and cost effective in clinical decision-making. The results held for reduced leads sets, suggesting that a simplified setup could also be considered, further reducing the costs. In designing the methods of this thesis, an online signal processing approach was kept, with the goal of contributing to real-world applicability. An algorithm for automatic assessment of ambulatory ECG quality, and an automatic ECG delineation algorithm were designed and validated.

From images to signs: Cretan Hieroglyphic and Linear A in context

This dissertation adopts a multidisciplinary approach to investigate graphical and formal features of Cretan Hieroglyphic and Linear A. Drawing on theories which understand inscribed artefacts as an interplay of materials, iconography, and texts, I combine archaeological and philological considerations with statistical and experimental observations. The work is formulated on three key-questions. The first deals with the origins of Cretan Hieroglyphic. After providing a fresh view on Prepalatial seals chronology, I identify a number of forerunners of Hieroglyphic signs in iconographic motifs attested among the Prepalatial glyptic and material culture. I further identified a specific style-group, i.e., the ‘Border and Leaf Complex’, as the decisive step towards the emergence of the Hieroglyphic graphic repertoire. The second deals with the interweaving of formal, iconographical, and epigraphic features of Hieroglyphic seals with the sequences they bear and the contexts of their usage. By means of two Correspondence Analyses, I showed that the iconography on seals in some materials and shapes is closer to Cretan Hieroglyphics, than that on the other ones. Through two Social Network Analyses, I showed that Hieroglyphic impressions, especially at Knossos, follow a precise sealing pattern due to their shapes and sequences. Furthermore, prisms with a high number of inscribed faces adhere to formal features of jasper ones. Finally, through experimental engravings, I showed differences in cutting rates among materials, as well as the efficiency of abrasives and tools unearthed within the Quartier Mu. The third question concerns overlaps in chronology, findspots and signaries between Cretan Hieroglyphic and Linear A. I discussed all possible earliest instances of both scripts and argued for some items datable to the MM I-IIA period. I further provide an insight into the Hieroglyphic-Linear A dubitanda and criteria for their interpretation. Finally, I suggest four different patterns in the creation and diversification of the two signaries.