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Subjective Visual Experiences of Colour and Form Induced by Temporally Modulated Light

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Subjective Visual Experiences of Colour and Form Induced by Temporally Modulated Light Subjective visual experiences of colour and form induced by temporally modulated light Cordula Becker M¨unchen2005 Subjective visual experiences of colour and form induced by temporally modulated light Cordula Becker Inaugural-Dissertation zur Erlangung des Doktorgrades der Philosophie an der Ludwig–Maximilians–Universit¨at M¨unchen vorgelegt von Cordula Becker aus Magdeburg M¨unchen, den 21.03.2005 Erstgutachter: Prof. Hermann J. M¨uller Zweitgutachter: Prof. Heiner Deubel Tag der m¨undlichen Pr¨ufung:29.06.2005 Ich hatte die Gabe, wenn ich die Augen schloß und mit niedergesenktem Haupte mir in die Mitte des Sehorgans eine Blume dachte, so verharrte sie nicht einen Augenblick in ihrer ersten Gestalt, sondern sie legte sich auseinander, und aus ihrem Inneren entfalteten sich wieder neue Blumen aus farbigen, auch wohl gr¨unen Bl¨attern;es waren keine nat¨urlichenBlumen, sondern phantastische, jedoch regel- m¨aßigwie die Rosetten der Bildhauer. Es war unm¨oglich,die hervorsprossende Sch¨opfungzu fixieren, hingegen dauerte sie so lange, als mir beliebte, ermattete nicht und verst¨arktesich nicht. Dasselbe konnte ich hervorbringen, wenn ich mir den Zierrat einer buntgemalten Scheibe dachte, welche dann ebenfalls aus der Mitte gegen die Peripherie hin sich immerfort ver¨anderte,v¨ollig wie die in unseren Tagen erst erfundenen Kaleidoskope. Johann Wolfgang von Goethe Studien zur Morphologie I wish to express my thanks to everyone who helped me during the various phases of writing this dissertation. I am thankful to Hermann M¨uller for the opportunity to do research and write a thesis in his group in Munich. I also wish to thank him and Heiner Deubel for their willingness to act as reviewers of this thesis. I am especially grateful to Mark Elliott for accepting me into his Psychophysics and Temporal Factors lab, introducing me to the paradigms employed in this thesis, his openness for discussions and support during all stages of experimentation, analysis, and writing of the thesis. My thanks go to Andreas Schiegg for his help on the electronic interface of the experimental apparatus, as well as to Sven Garbade for sharing his expertise on the statistical programming language R. For the revealing insights into electroencephalographic experiments, as well as for practical help concerning EEG experiments and analyses, I wish to thank Klaus Gramann. This work could not have been realized without the help of my student helpers Christine Falter, Marieluise Hupfauer, Katerina Obermeier, and Bernhard Ostler. Many thanks to them and to all brave and patient volunteers who participated in my experiments. Many thanks for proofreading the German summary to Stefanie Arndt. Special thanks go to to my Bavarian colleagues for their introduction to Bavarian life and civilisation, in particular a primer to the Bavarian language and induction to the ”Biergarten” culture. I thank Johannes for proofreading and support throughout. Contents 1 Introduction 1 1.1 An overview of subjective visual experiences ............ 4 1.1.1 Historical and religious reports of subjective visual experiences 4 1.1.2 Clinical descriptions of subjective visual experiences . 6 1.1.3 Magnetically and electrically induced subjective visual ex- periences ............................ 9 1.2 Subjective visual experiences induced by visual stimulation . 12 1.2.1 Benham’s Top and Benham-like stimulation regimes . 14 1.2.2 Stimulation of the visual ganzfeld . 19 1.3 Physiological mechanisms of visual perception related to subjective experiences .............................. 24 1.3.1 Mechanisms of colour perception . 24 1.3.2 Mechanisms of form perception . 30 1.3.3 Physiological models of subjective visual experiences . 33 1.4 Overview of the thesis ........................ 39 2 Descriptive analysis of visually induced subjective experiences 43 2.1 Rationale ............................... 44 2.2 Methods ................................ 44 2.3 Results ................................. 46 2.3.1 Reported categories of colour and form . 46 2.3.2 Analysis of the distribution of subjective experiences over frequency ........................... 48 2.4 Discussion ............................... 51 3 Interdependencies in the appearance of subjective visual experi- ences 54 3.1 A multidimensional model of co-occurrent subjective visual expe- riences ................................. 55 3.1.1 Rationale ........................... 55 3.1.2 Methods of analysis ...................... 55 3.1.3 Results ............................. 58 3.1.4 Discussion ........................... 62 3.2 Progression of subjective visual experiences over time . 63 3.2.1 Rationale ........................... 63 3.2.2 Methods of analysis ...................... 63 3.2.3 Results ............................. 64 3.2.4 Discussion ........................... 67 4 Relation of subjective visual experiences to the temporal charac- teristics of the stimulation 68 4.1 Rationale ............................... 69 4.2 Methods ................................ 70 4.3 Results ................................. 71 4.3.1 Analysis of the distributions of subjective experiences over frequency ........................... 71 4.3.2 Response time analysis .................... 72 4.3.3 Analysis of response times over phase . 73 4.4 Discussion ............................... 76 5 Spontaneous visual experiences during constant ganzfeld stimu- lation 77 5.1 Rationale ............................... 78 5.2 Methods ................................ 78 5.3 Results ................................. 80 5.3.1 Descriptive analysis of spontaneous visual experiences in free report ........................... 80 5.3.2 Impact of the results of Experiment 4 and 5 on the findings of Experiment 1 ........................ 81 5.3.3 Descriptive analysis of spontaneous visual experiences in a forced-choice paradigm .................... 85 5.3.4 Impact of the results of Experiment 4 and 5 on the findings of Experiment 2 and 3 .................... 87 5.4 Discussion ............................... 89 6 Phenomenology of subjective visual experiences 91 6.1 Description of subjective colours ................... 92 6.1.1 Rationale ........................... 92 6.1.2 Methods ............................ 92 6.1.3 Results ............................. 99 6.1.4 Discussion . 105 6.2 Description of subjective forms . 107 6.2.1 Rationale . 107 6.2.2 Methods ............................ 107 6.2.3 Results ............................. 108 6.2.4 Discussion . 112 7 Electrophysiological correlates of subjective colour 114 7.1 Rationale ............................... 115 7.2 Methods ................................ 118 7.3 Results ................................. 123 7.4 Discussion ............................... 126 8 General Discussion 130 8.1 Summary of the experimental evidence . 131 8.2 A theoretical model of subjective colour . 133 8.3 Mechanisms of subjective form and the relation between subjective colour and form ............................ 137 8.4 Future prospects . 139 A Form of consentment 141 B Instructions 143 C Experiment 1 - Sizer plots 162 D Experiment 1 - Kolmogorov-Smirnov-tests 165 E Experiment 1 - Multidimensional scaling 167 F Experiment 2 and 3 - Circular plots 195 G Experiment 4 and 5 - SiZer plots 198 H Experiment 7 - Drawings of subjective forms 201 I Experiment 8 - EEG regression formulas 241 German summary/Deutsche Zusammenfassung 257 Bibliography 272 Curriculum Vitae 289 Chapter 1 Introduction 1 Introduction Conscious visual experience relies on the interaction of our nervous system with light reflected from spatial structures in the environment. It is often assumed that the visual experiences resulting from this interaction are directly related to the characteristics of the external stimulus, so that for example spatial properties of the external stimulus are directly mapped onto spatial properties of the internal experience. This approach already fails when considering colour perception, where the internal visual experience cannot be mapped directly onto the external physi- cal properties in terms of light reflectance and light absorbance of objects. Colour metamers, for example, are pairs of perceptually indistinguishable colours based on the interaction of the visual system with light of different physical properties, i.e. spectral distributions [2]. Some recent philosophical-psychological debates on the subjectivity of colour experiences (see [3] and [4] and the related discussions) shed some light on the controversial potential of this mapping problem. While some philosophers believe in the absolute subjectivity of colour experience (e.g. Hardin [5]), that is the impossibility to describe colour in physical terms, Ross [3, 6], as well as Byrne and Hilbert [4] argue that subjectivism is not tenable on philosophical grounds and therefore colours have to be seen as objective physical properties of the external world. In contrast, some psychological perspectives on the problem [7, 8] follow a causal theory of perception. This approach states that colours are located at the end of a causal chain from (i) the distal external stim- ulus (i.e. the physical object with its physical properties), via (ii) the proximal stimulus (i.e. the stimulus on the retina), and (iii) the direct neural correlates of colour (i.e. the states of the nervous system) to (iv) the experience of colour (residing in the conscious visual experience). While the stages (ii) and (iii) clearly involve interactions between the external stimulus properties and the nervous sys- tem, the
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