Perceptual multistability is a phenomenon that is mostly studied in all modalities separately. The phenomenon reveals fundamental principles of the perceptual system in the formation of an emerging cognitive representation in the consciousness. The momentary perceptual organizations evoked during the stimulation with ambiguous stimuli switches between several perceptual organizations or percepts: The auditory streaming stimulus in audition and the moving plaids stimulus in vision, elicit different at least two percepts that dominate awareness exclusively for a random phase or dominance duration before an inevitable switch to another percept occurs. The similarity in the perceptual experience has led to propose a global mechanism contributing to the perceptual multistability phenomena crossmodally. Contrary, the difference in the perceptual experience has led to propose a distributed mechanism that is modality-specific. The development of a hybrid model has synergized both approaches. We accumulate empirical evidence for the contribution of a global mechanism, albeit distributed mechanisms play an indispensable role in this cross-modal interplay. The overt report of the perceptual experience in our experiments is accompanied by the recording of objective, cognitive markers of the consciousness: Reflexive movements of the eyes, namely the dilation of the pupil and the optokinetic nystagmus, correlate with the unobservable perceptual switches and perceptual states respectively and have their neuronal rooting in the brainstem. We complement earlier findings on the sensitivity of the pupil to visual multistability: It was shown in two independent experiments that the pupil dilates at the time of reported perceptual switches in auditory multistability. A control condition on confounding effects from the reporting process confines the results. Endogenous, evoked internally by the unchanged stimulus ambiguity, and exogenous, evoked externally by the changes in the physical properties of the stimulus, perceptual switches could be discriminated based on the maximal amplitude of the dilation. The effect of exogenous perceptual has on the pupil were captured in a report and no-report task to detect confounding perceptual effects. In two additional studies, the moment-by-moment coupling and coupling properties of percepts between concurrent multistable processes in audition, evoked by auditory streaming, and in vision, evoked by moving plaids, were found crossmodally. In the last study, the externally induced percept in the visual multistable process was not relayed to the simultaneous auditory multistable process: Still, the observed general coupling is fragile but existent. The requirement for the investigation of a moment-by-moment coupling of the multistable perceptual processes was the application of a no-report paradigm in vision: The visual stimulus evokes an optokinetic nystagmus that has machine learnable different properties when following either of the two percepts. In combination with the manually reported auditory percept, attentional bottlenecks due to a parallel report were circumvented. The two main findings, the dilation of the pupil along reported auditory perceptual switches and the crossmodal coupling of percepts in bimodal audiovisual multistability, speak in favor of a partly global mechanism being involved in control of perceptual multistability; the global mechanism is incarcerated by the, partly independent, distributed competition of percepts on modality level. Potentially, supramodal attention-related modulations consolidate the outcome of locally distributed perceptual competition in all modalities.:COVER 1 BIBLIOGRAPHISCHE BESCHREIBUNG 2 ACKNOWLEDGEMENTS 3 CONTENTS 4 CHAPTER 1: Introduction 6 C1.1: Stability and uncertainty in perception 6 C1.2: Auditory, visual and audio-visual multistability 14 C1.3: Capturing the subjective perceptual experience 25 C1.4: Limitations of preceding studies, objectives, and outline of the Thesis 33 CHAPTER 2: Study 1 “Pupillometry in auditory multistability” 36 C2.1.1 Experiment 1: Introduction 36 C2.1.2 Experiment 1: Material and Methods 38 C2.1.3 Experiment 1: Data analysis 44 C2.1.4 Experiment 1: Results 48 C2.1.5 Experiment 1: Discussion 52 C2.2.1 Experiment 2: Introduction 54 C2.2.2 Experiment 2: Material and Methods 54 C2.2.3 Experiment 2: Data analysis 56 C2.2.4 Experiment 2: Results 57 C2.3 Experiment 1 & 2: Discussion 61 C2.4 Supplement Study 1 65 CHAPTER 3: Study 2 “Multimodal moment-by-moment coupling in perceptual bistability” 71 C3.1.1 Experiment 1: Introduction 71 C3.1.2 Experiment 1: Results 74 C3.1.3 Experiment 1: Discussion 80 C3.1.4 Experiment 1: Material and Methods 84 C3.1.5 Experiment 1: Data analysis 87 C3.2 Supplement Study 2 92 CHAPTER 4: Study 3 “Boundaries of bimodal coupling in perceptual bistability” 93 C4.1.1 Experiment 1: Introduction 93 C4.1.2 Experiment 1: Material and Methods 98 C4.1.3 Experiment 1: Data analysis 102 C4.1.4 Experiment 1: Results 108 C4.1.5 Experiment 1: Discussion 114 C4.2.1 Experiment 2: Introduction 116 C4.2.2 Experiment 2: Material and Methods 119 C4.2.3 Experiment 2: Data analysis 125 C4.2.4 Experiment 2: Results 133 C4.3 Experiment 1 & 2: Discussion 144 C4.4 Supplement Study 3 151 CHAPTER 5: General Discussion 154 C5.1 Significance for models of multistability and implications for the perceptual architecture 162 C5.2 Recommendations for future research 166 C5.3 Conclusion 168 REFERENCES 170 APPENDIX 186 A1: List of Figures 186 A2: List of Tables 188 A3: List of Abbreviations and Symbols 189

Belohnungen sind im Leben des Menschen von enormer Bedeutung. Es wurde vermutet, dass die zentralen sozialen Schwierigkeiten bei Autismus-Spektrum-Störungen (ASS) auf eine verminderte Reaktionsfähigkeit auf spezifische soziale Belohnungen zurückzuführen sein könnten. Die Literatur zu diesem Thema ist jedoch nicht schlüssig. Diese Dissertation umfasst vier Studien, die die Reaktionsfähigkeit auf soziale und nicht-soziale Belohnungen unter besonderer Berücksichtigung von ASS und autistischen Merkmalen untersuchen. In den Studien 1 und 2 wurden neuronale (ereigniskorrelierte Potenziale), autonome (Pupillengröße) und verhaltensbezogene (Selbstberichte und Reaktionszeiten) Indizes der Reaktion auf soziale und nicht-soziale Belohnungen bei Personen mit ASC sowie mit ausgeprägten und geringen autistischen Merkmalen untersucht. Wir stellten fest, dass ein höheres Maß an autistischen Merkmalen bei klinischen ASS und in der Allgemeinbevölkerung mit einer verstärkten neuronalen und autonomen Verarbeitung, typischen Leistungen und einer geringeren selbstberichteten Belohnungssensitivität verbunden war. Studie 3 untersuchte die Auswirkungen von sozialer Vertrautheit und Belohnungskontext auf die Pupillenreaktionen. Die Ergebnisse deuten darauf hin, dass der Belohnungswert eines positiven Reizes bei vertrauten Gesichtern höher ist und von der Assoziation zwischen Handlung und Ergebnis abhängt. Studie 4 ist eine theoretische Perspektive zum Verständnis der Multidimensionalität von Belohnungen und zum Umgang damit. In allen Studien konnte ich nachweisen, dass das Belohnungsverhalten von ASS vielfältig und atypisch, aber nicht defizitär ist. Außerdem schlage ich eine Definition von Belohnung vor, die sie von einem rein positiven Stimulus unterscheidet. Schließlich erörtere ich diese Arbeit im breiteren Rahmen der sozialneuropsychologischen Forschung und zeige Möglichkeiten auf, wie sie in künftigen Studien weiter verbessert werden kann. / Rewards are immensely important in human lives. It has been suggested that the core social difficulties in autism spectrum conditions (ASC) may stem from lowered responsiveness to specifically social rewards. However, the literature on this topic is inconclusive. This dissertation includes four studies investigating reward responsiveness to social and non-social rewards with particular focus on ASC and autistic traits. Studies 1 and 2 investigated neuronal (event-related potentials), autonomic (pupil sizes) and behavioural (self-reports and reaction times) indexes of responsiveness to social and non-social rewards in individuals with ASC, and with high and low autistic traits. We observed that higher levels of autistic traits in clinical ASC and in the general population were linked to enhanced neuronal and autonomic processing, typical performance, and decreased self-reported reward sensitivity. Study 3 investigated the effects of social familiarity and rewarding context on pupillary responses. The results indicated that the reward value of a positive stimulus is higher for more familiar faces and depends on action-outcome associations. Study 4 is a theoretical perspective on understanding and working with multidimensionality of rewards. Across all studies, I provide evidence for multifaceted and atypical, but not deficient, reward responsiveness in ASC. Further, I propose a definition of reward which differentiates it from a merely positive stimulus. Finally, I discuss this work in the broader framework of social neuropsychology research and identify the ways in which it can be further improved in future studies.