Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

This thesis explores the field of light, space and human perception. Human perception is an active, information-seeking process, but when this information is not clear our mind tries to fool us by filling the emptiness. This unclear structure is also called the Ganzfeld effect. When being exposed to the Ganzfeld effect hallucinations may occur. The experiment set up for this thesis was to see if a stimulus of light could be used to prevent the mind drifting off into hallucinations and keeping a clear understanding of the space. Based on previous literature research two experiments were set up. In the first experiment I expored myself how the Ganzfeld in nature affected me. In the second experiment six participants including myself experienced the Ganzfeld effect combined with a low light stimulus.  This thesis concludes that an exposure to the Ganzfeld effect in combination with a low light stimulus prevents from complete hallucinations. When using a light stimulus an inbetween world is created. A clear description of this reality in spatial terms was attempted. Without the light stimulus the mind was able to drift off and went into an unreal world. When a light stimulus was given, the mind went back to the real and the space could be clearly understood.

Les déficits cognitifs sont centraux à la psychose et sont observables plusieurs années avant le premier épisode psychotique. L’atteinte de la mémoire épisodique est fréquemment identifiée comme une des plus sévères, tant chez les patients qu’avant l’apparition de la pathologie chez des populations à risque. Chez les patients psychotiques, l’étude neuropsychologique des processus mnésiques a permis de mieux comprendre l’origine de cette atteinte. Une altération des processus de mémoire de source qui permettent d’associer un souvenir à son origine a ainsi été identifiée et a été associée aux symptômes positifs de psychose, principalement aux hallucinations. La mémoire de source de même que la présence de symptômes sous-cliniques n’ont pourtant jamais été investiguées avant l’apparition de la maladie chez une population à haut risque génétique de psychose (HRG). Or, leur étude permettrait de voir si les déficits en mémoire de source de même que le vécu d’expériences hallucinatoires sont associés à l’apparition de la psychose ou s’ils en précèdent l’émergence, constituant alors des indicateurs précoces de pathologie. Afin d’étudier cette question, trois principaux objectifs ont été poursuivis par la présente thèse : 1) caractériser le fonctionnement de la mémoire de source chez une population HRG afin d’observer si une atteinte de ce processus précède l’apparition de la maladie, 2) évaluer si des manifestations sous-cliniques de symptômes psychotiques, soit les expériences hallucinatoires, sont identifiables chez une population à risque et 3) investiguer si un lien est présent entre le fonctionnement en mémoire de source et la symptomatologie sous-clinique chez une population à risque, à l’instar de ce qui est documenté chez les patients. Les résultats de la thèse ont permis de démontrer que les HRG présentent une atteinte de la mémoire de source ciblée à l’attribution du contexte temporel des souvenirs, ainsi que des distorsions mnésiques qui se manifestent par une fragmentation des souvenirs et par une défaillance de la métacognition en mémoire. Il a également été observé que les expériences hallucinatoires sous-cliniques étaient plus fréquentes chez les HRG. Des associations ont été documentées entre certaines distorsions en mémoire et la propension à halluciner. Ces résultats permettent d’identifier de nouveaux indicateurs cliniques et cognitifs du risque de développer une psychose et permettent de soulever des hypothèses liant l’attribution de la source interne-externe de l’information et le développement de la maladie. Les implications empiriques, théoriques, méthodologiques et cliniques de la thèse sont discutées. / Cognitive deficits are at the core of psychosis and are observed before the onset of the disease. Episodic memory deficits are frequently reported to be among the most severe impairments, both in patients and in at risk populations. In psychotic patients, a refined analysis of episodic memory within a neuropsychological framework allowed for a better understanding of the specific altered processes. Previous studies of psychotic patients showed dysfunctions of source memory processes, which are responsible for the attribution of memories to their specific origin, that were associated with psychotic positive symptoms, especially hallucinations. However, source memory processes and subclinical hallucinatory-like experiences have never been studied before the onset of psychosis in offspring at genetic high risk of psychosis (GHR). It is still unknown if source memory alterations and subclinical symptoms appear at the onset of psychosis or if they precede it, therefore being an early marker of risk. To address this issue, three main objectives were pursued in the present thesis: 1) to examine if an alteration of source memory precede the onset of psychosis by characterizing source memory functioning in GHR, 2) to assess if subclinical hallucinatory-like experiences are present in this at-risk population and 3) to evaluate if source memory and hallucinatory experiences are associated in a GHR population, as seen in patients. Findings of the thesis showed that GHR have impaired source memory functioning, specifically in the retrieving of the temporal context of souvenirs, and present memory distortions as showed by an alteration in the binding of memories and in metacognition processes. It was also observed that GHR experience hallucinatory-like experiences more frequently than controls. Associations were found between hallucination proneness and distortions in source memory. Those results contribute to the identification of new cognitive and clinical markers of psychosis and suggest a specific association between the attribution of internal-external source of information and the development of psychosis. Empirical, theoretical, methodological and clinical contributions of this thesis are discussed.

Le présent mémoire s' inscrit dans le cadre d'une recherche plus vaste menée par l'organisme le Pavois sur l'évaluation d'un groupe pour les entendeurs de voix. La démarche de groupe, qui comporte une dimension d'éducation et de soutien, s'est déroulée sur une période de douze semaines. S'inspirant d'un paradigme phénoménologique, cette recherche qualitative a pour objectif de vérifier les effets de la méthode de groupe auprès des participants, et vise également à approfondir les connaissances sur ce que les entendeurs de voix expérimentent en décrivant les diverses caractéristiques et croyances associées aux voix (leur contenu, leur identité, etc.). Pour ce faire, des entrevues en profondeur ont été réalisées auprès de six participants à ce groupe, c'est-à-dire cinq femmes et un homme dont la durée de l'audition des voix varie entre 5 et 30 ans. Les résultats obtenus révèlent notamment que les voix se manifestent fréquemment, que les-répondants entendent plus d'une voix et qu'elles sont majoritairement féminines. Le contenu des voix est rarement neutre sur le plan affectif et il comporte généralement des directives, des conseils, des critiques, etc. Les données indiquent, par ailleurs, que l'un des besoins qu'éprouvent les répondants s'inscrit sur le plan de la communication, en ce sens qu'ils ont fait ressortir l'importance de partager cette expérience perceptuelle avec d'autres personnes, mais qu'ils se heurtent à plusieurs obstacles environnementaux (tabous, stigmatisation ... ) de sorte qu'ils en parlent rarement. Par conséquent, l'étude démontre que le groupe pour les entendeurs de voix constitue pour les participants un cadre propice pour échanger sur ce type d'expérience, et qu'ils en retirent également d'autres bénéfices, tels que l'amélioration de leur répertoire de stratégies d'adaptation pour composer avec les voix, la normalisation de leur expérience perceptuelle, etc.

- / The diagnosis of hallucination for unusual perceptions such as deathbed visions, near-death experiences, or visions of the bereaved, is unhelpful in palliative medicine both academically and clinically. This paper reviews the broad prevalence data about unusual perceptions in the general population as to identifying the more narrow epidemiological source from which the much smaller focus on hallucinations seem to emerge. Major debates and limitations of current hallucination research are reviewed to show that current academic and clinical certainties are largely confined to unusual perceptions that can be readily linked to psychopathology, quite specific organic disease states and psychoactive drug use. Current state-of-the-art in hallucination studies does not warrant broad or uncritical use of this type of diagnosis in end-of-life care. Conclusions from interdisciplinary (as opposed to single discipline) hallucination studies suggest that the way forward for clinical and research work in palliative medicine may lie in a more biographical and cultural approach to unusual perceptions at the end of life.

No description available.

Au cours de mon programme doctoral j'ai mené plusieurs recherches, à la fois conceptuelles et empiriques, se rapportant à deux champs d'investigation importants des sciences cognitives : la schizophrénie et la métacognition. Ma dissertation se divise en deux grandes parties. La première partie inclue 3 études expérimentales (deux études menées sur des échantillons de sujets sains et une étude menée sur des individus atteints de schizophrénie) ainsi que deux études théoriques adressant des aspects spécifiques de la schizophrénie. La seconde partie présente quatre études théoriques portant sur l'apport de la métacognition dans certains débats vigoureux présents au sein de la philosophie analytique et des sciences cognitives. J'ai donc exploré deux symptômes de la schizophrénie -l'insertion de pensées et les expériences d'activité- ainsi qu'un potentiel biais cognitif ; à savoir, la présence de phénomènes aberrants de persistance perceptive. En ce qui concerne le thème de la métacognition, j'ai examiné la manière dont les sentiments métacognitifs (l'output phénoménologique des processus métacognitifs) pouvaient éclairer d'une nouvelle lumière certains débats importants de la philosophie et des sciences cognitives. Je me suis ainsi concentré tour à tour sur le problème des hallucinations ; sur le débat concernant la pénétrabilité cognitive (l'hypothèse que nos croyances peuvent influencer profondément nos expériences perceptives) ; sur la perception des absences et sur le cas de la substitution sensorielle. / Over the course of my PhD I have investigated issues related to two main areas of investigation in cognitive science, namely Schizophrenia and Metacognition. My dissertation is divided in two parts: the first part includes three experimental studies (two studies in healthy subjects and one study in people with schizophrenia) and two theoretical studies addressing specific aspects of schizophrenia; the second part includes four theoretical studies addressing the role of metacognition in specific debates in philosophy and cognitive science of perception. I have explored two symptomatic expressions of schizophrenia, thought insertion and experiences of activity, as well as a potential cognitive bias, namely the potential presence of perceptual persistence biases. With respect to metacognition, I have investigated ways in which consideration of the role of metacognitive feelings (the experiential output of metacognitive processes) could shed new light on important current debates in analytical philosophy and cognitive science. The issues I have focused on are: the problem of hallucinations, the debate about cognitive penetrability (i.e., whether or not higher-order cognitive states may influence perceptual processes), the perception of absences and sensory substitution.

Objective: To examine the hypothesis that the “natural” combination of delusions and hallucinations in psychotic disorders in fact represents a selection of early subclinical hallucinatory experiences associated with delusional ideation, resulting in need for care and mental health service use. Methods: In the Early Developmental Stages of Psychopathology study, a prospective, 10-year follow-up of a representative cohort of adolescents and young adults in Munich, Germany (n = 2524), clinical psychologists assessed hallucinations and delusions at 2 time points (T2 and T3). Analyses compared differences in psychopathology, familial liability for nonpsychotic disorder, nongenetic risk factors, persistence, and clinical outcome between groups characterized by: (1) absence of positive psychotic symptoms, (2) presence of isolated hallucinations, (3) isolated delusions, and (4) both hallucinations and delusions. Results: Delusions and hallucinations occurred together much more often (T2: 3.1%; T3: 2.0%) than predicted by chance (T2: 1.0%; T3: 0.4%; OR = 11.0; 95% CI: 8.1, 15.1). Content of delusions was contingent on presence of hallucinations but modality of hallucinations was not contingent on presence of delusions. The group with both hallucinations and delusions, compared to groups with either delusions or hallucinations in isolation, displayed the strongest associations with familial affective liability and nongenetic risk factors, as well as with persistence of psychotic symptoms, comorbidity with negative symptoms, affective psychopathology, and clinical need. Conclusions: The early stages of psychosis may involve hallucinatory experiences that, if complicated by delusional ideation under the influence of environmental risks and (liability for) affective dysregulation, give rise to a poor prognosis hallucinatory–delusional syndrome.

Background The base rate of transition from subthreshold psychotic experiences (the exposure) to clinical psychotic disorder (the outcome) in unselected, representative and non-help-seeking population-based samples is unknown. Method A systematic review and meta-analysis was conducted of representative, longitudinal population-based cohorts with baseline assessment of subthreshold psychotic experiences and follow-up assessment of psychotic and non-psychotic clinical outcomes. Results Six cohorts were identified with a 3–24-year follow-up of baseline subthreshold self-reported psychotic experiences. The yearly risk of conversion to a clinical psychotic outcome in exposed individuals (0.56%) was 3.5 times higher than for individuals without psychotic experiences (0.16%) and there was meta-analytic evidence of dose–response with severity/persistence of psychotic experiences. Individual studies also suggest a role for motivational impairment and social dysfunction. The evidence for conversion to non-psychotic outcome was weaker, although findings were similar in direction. Conclusions Subthreshold self-reported psychotic experiences in epidemiological non-help-seeking samples index psychometric risk for psychotic disorder, with strong modifier effects of severity/persistence. These data can serve as the population reference for selected and variable samples of help-seeking individuals at ultra-high risk, for whom much higher transition rates have been indicated.

Computational modelling has been gaining an increasing amount of support from the neuroscience community as a tool to assay cognition and computational processes in the brain. Lately, scientists have started to apply computational methods from neuroscience to the study of psychiatry to gain further insight into the mechanisms leading to mental disorders. In fact, only recently has psychiatry started to move away from categorising illnesses using behavioural symptoms in an attempt for a more biologically driven diagnosis. To date, several neurobiological anomalies have been found in schizophrenia and led to a multitude of conceptual framework attempting to link the biology to the patients’ symptoms. Computational modelling can be applied to formalise these conceptual frameworks in an effort to test the validity or likelihood of each hypothesis. Recently, a novel conceptual model has been proposed to describe how positive symptoms (delusions, hallucinations and thought disorder) and cognitive symptoms (poor decision-making, i.e. “executive functioning”) might arise in schizophrenia. This framework however, has not been tested experimentally or against computational models. The focus of this thesis was to use a combination of behavioural experiments and computational models to independently assess the validity of each component that make up this framework. The first study of this thesis focused on the computational analysis of a disrupted prediction-error signalling and its implications for decision-making performances in complex tasks. Briefly, we used a reinforcement-learning model of a gambling task in rodents and disrupted the prediction-error signal known to be critical for learning. We found that this disruption can account for poor performances in decision-making due to an incorrect acquisition of the model of the world. This study illustrates how disruptions in prediction-error signalling (known to be present in schizophrenia) can lead to the acquisition of an incorrect world model which can lead to poor executive functioning or false beliefs (delusions) as seen in patients. The second study presented in this thesis addressed spatial working memory performances in chronic schizophrenia, bipolar disorder, first episode psychosis and family relatives of DISC1 translocation carriers. We build a probabilistic inference model to solve the working memory task optimally and then implemented various alterations of this model to test commonly debated hypotheses of cognitive deficiency in schizophrenia. Our goal was to find which of these hypotheses accounts best for the poor performance observed in patients. We found that while the performance at the task was significantly different for most patients groups in comparison to controls, this effect disappeared after controlling for IQ in one group. The models were nonetheless fitted to the experimental data and suggest that working memory maintenance is most likely to account for the poor performances observed in patients. We propose that the maintenance of information in working memory might have indirect implications for measures of general cognitive performance, as these rely on a correct filtering of information against distractions and cortical noise. Finally the third study presented in this thesis assessed the performance of medicated chronic schizophrenia patients in a statistical learning task of visual stimuli and measured how the acquired statistics influenced their perception. We find that patient with chronic schizophrenia appear to be unimpaired at statistical learning of visual stimuli. The acquired statistics however appear to induce less expectation-driven ‘hallucinations’ of the stimuli in the patients group than in controls. We find that this is in line with previous literature showing that patients are less susceptible to expectation-driven illusions than controls. This study highlights however the idea that perceptual processes during sensory integration diverge from this of healthy controls. In conclusion, this thesis suggests that impairments in reinforcement learning and Bayesian inference appear to be able to account for the positive and cognitive symptoms observed in schizophrenia, but that further work is required to merge these findings. Specifically, while our studies addressed individual components such as associative learning, working memory, implicit learning & perceptual inference, we cannot conclude that deficits of reinforcement learning and Bayesian inference can collectively account for symptoms in schizophrenia. We argue however that the studies presented in this thesis provided evidence that impairments of reinforcement learning and Bayesian inference are compatible with the emergence of positive and cognitive symptoms in schizophrenia.