Pupil size is governed by the Autonomic Nervous System, precisely by both its branches, the Parasympathetic and Sympathetic Systems. The iris-pupil structure is a perfect example of this combined working: two set of antagonistic smooth muscles work in order to constrict (‘miosis’) or dilate (‘mydriasis’) the iris in order to determine its size. Pupil Diameter is primarily influenced by the light level and it is responsive to variations of global luminance level. However, recent studies have shown that there is also a high-level interpretation which could modulate this physiological response. Starting from these assumptions, the aim of this thesis is to develop an ad-hoc protocol and test it for future evaluation of comatose or generic unconscious state through analysis of high-level modulation of pupil response, based on iso-luminant stimuli. Thus, a visual illusion was taken from literature and adapted in different colors and simulated distances (dimensions). Alongside the pupil signal (PS), the ECG of the subjects was also recorded. Prior to the response analysis, a reconstruction of the missing data due to blinks and other artifacts was made using a recently developed signal reconstruction algorithm (Iterative – Single Spectrum Analysis: I-SSA); then both time and frequency domain parameters were extracted from pupil signal. Results indicate that there is a different pupillary response to iso-luminant stimuli, higher in certain colors and dimension. Also, through the spectral coherence analysis of PS and RR series, we confirmed the existence of a correlation between the two signals, already shown in literature.
La dimensione della pupilla è governata dal Sistema Nervoso Autonomo, precisamente da entrambe le sue branche, il sistema Simpatico e quello Parasimpatico. La struttura iride-pupilla è un perfetto esempio di questo lavoro congiunto: due gruppi di muscoli lisci antagonisti collaborano per contrarre (miosi) o dilatare (midriasi) l'iride per determinare la sua dimensione. Il diametro pupillare è principalmente influenzato dal livello di luce ed è sensibile alle variazioni di luminanza globale. Tuttavia, studi recenti hanno mostrato che esiste anche un'interpretazione ad alto livello che potrebbe modulare questa risposta fisiologica. Partendo da queste ipotesi, lo scopo di questa tesi è sviluppare un protocollo ad-hoc e testarlo per una futura valutazione di stati inconsci (comatosi e generici) attraverso l'analisi della modulazione ad alto livello della risposta pupillare. Quindi, è stata ripresa dalla letteratura un'illusione visiva e rivisitata in diversi colori e distanze simulate (dimensioni). Assieme al segnale pupillare, è stato registrato per ogni soggetto anche il segnale ECG. Prima di analizzare la risposta, sono stati ricostruiti i dati mancanti dovuti ai blink e ad altri artefatti utilizzando un algoritmo di ricostruzione del segnale sviluppato recentemente (Iterative - Single Spectrum Analysis: I-SSA); poi, sono stati estratti i parametri sia nel dominio temporale che in frequenza. I risultati indicano la presenza di una diversa risposta pupillare agli stimoli ad isoluminanza, in maniera maggiore in determinati colori e dimensioni. Inoltre attraverso l'analisi della coerenza spettrale è stata confermata l'esistenza di una correlazione tra i due segnali, già mostrata in letteratura.
A pupil dynamics acquisition and processing framework for assessment of high-level response to iso-luminant stimuli
BRAMBILLA, RICCARDO
2016/2017
Abstract
Pupil size is governed by the Autonomic Nervous System, precisely by both its branches, the Parasympathetic and Sympathetic Systems. The iris-pupil structure is a perfect example of this combined working: two set of antagonistic smooth muscles work in order to constrict (‘miosis’) or dilate (‘mydriasis’) the iris in order to determine its size. Pupil Diameter is primarily influenced by the light level and it is responsive to variations of global luminance level. However, recent studies have shown that there is also a high-level interpretation which could modulate this physiological response. Starting from these assumptions, the aim of this thesis is to develop an ad-hoc protocol and test it for future evaluation of comatose or generic unconscious state through analysis of high-level modulation of pupil response, based on iso-luminant stimuli. Thus, a visual illusion was taken from literature and adapted in different colors and simulated distances (dimensions). Alongside the pupil signal (PS), the ECG of the subjects was also recorded. Prior to the response analysis, a reconstruction of the missing data due to blinks and other artifacts was made using a recently developed signal reconstruction algorithm (Iterative – Single Spectrum Analysis: I-SSA); then both time and frequency domain parameters were extracted from pupil signal. Results indicate that there is a different pupillary response to iso-luminant stimuli, higher in certain colors and dimension. Also, through the spectral coherence analysis of PS and RR series, we confirmed the existence of a correlation between the two signals, already shown in literature.| File | Dimensione | Formato | |
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2017_12_Brambilla.pdf
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https://hdl.handle.net/10589/137873