VISUAL ILLUSIONS: PERCEPTION OF LUMINANCE, COLOR, AND MOTION IN HUMANS Inaugural-Dissertation zur Erlangung des akademischen Grades Doctor rerum naturalium (Dr. rer. nat.) an der Justus-Liebig-Universität Giessen Fachbereich 06: Psychologie und Sportwissenschaften Otto-Behaghel-Strasse 10F 35394 Giessen vorgelegt am 21. Dezember 2006 von Dipl. Psych. Kai Hamburger geboren am 5. Juni 1977 in Gedern 1. Berichterstatter und Betreuer Prof. Karl R. Gegenfurtner, Ph.D. (Psychologie, Giessen) 2. Berichterstatter Prof. Dr. Hans Irtel (Psychologie, Mannheim) To my grandfather Heinrich, my parents Elke and Rainer, my brother Sven, and to my fiancée Sandra. Acknowledgement First of all, I would like to express my gratitude to my godfather in the graduate program, Professor Karl R. Gegenfurtner (Giessen, Germany), and my two other supervisors, Professor Lothar Spillmann (Freiburg, Germany) and Professor Arthur G. Shapiro (Lewisburg, PA, U.S.A.). Karl, on very short notice you gave me the opportunity to join the graduate program ‘Neural Representation and Action Control – Neuroact’ and by doing so one of the best departments in the field of Vision Sciences. I became a member of an extraordinary lab, which still excites me. You allowed me to finish projects which were already in progress when I started in Giessen and you gave me plenty of rope to pursue my own interests. Thus, I was able to publish efficiently and furthermore gained deep insights into the field of Vision Sciences and even beyond. This was the best mentoring a natural scientist could think of. Thank you. Professor Spillmann, you paved my way into the Vision Sciences. At the beginning of my scientific career you gave me the opportunity to join your famous ‘Freiburg Psychophysics Laboratory’. There, I was working on many fascinating and challenging projects. Furthermore, I could work with scientists from all around the world and establish precious connections. Throughout my doctoral student period you supported me as much as possible. Even after I moved from Freiburg, you continued to support me, no matter where on earth you had been. Thank you. Arthur, you gave me the opportunity to work with a great ‘Illusionist’ as well as to obtain experience in a foreign country for an extended period of time. From the beginning of my stay, you treated me like a family member. I had a wonderful and productive time at Bucknell University. Zelda’s was our favorite and most fruitful place. I never thought that science could have this other side. Thank you. Professor Svein Magnussen (Oslo/Norway) offered me to take part in one of his projects. I gave my best. Professor Viktor Sarris (Frankfurt, Germany), PD Dr. Helmut Prior (Frankfurt, Germany), and Dr. Herbert Götzl (Bochum, Germany) supported certain projects as co-authors. Thank you. I also would like to thank all the anonymous reviewers who helped me improving my manuscripts with their critical questions and comments. I would also like to thank my fellow PhD students for their physical and mental support: Dr. Tobias Otte (Freiburg/Frankfurt, Germany), Cathi Hindi Attar (Freiburg/Leipzig, Germany), Simone Gori (Freiburg, Germany/Padua, Italy) and my Giessen office Room 307, namely Jutta Billino, Constanze Hesse – does anyone have chocolate? –, Lukas Kaim, and my former colleague Dr. Denise D.J. deGrave (Giessen, Germany/Amsterdam, Netherlands). I also thank Dr. Christoph Rasche from the office next door. iv For advice on the different manuscripts I would like to thank Professors Peter DeWeerd, Frank Durgin, Sir Richard L. Gregory, Stephen Grossberg, William S. Huff, Sergio C. Masin, Heiko Neumann, Hans-Christoph Nothdurft, Sriman R. Tripathy, Christopher W. Tyler, John S. Werner, as well as Doctors Cornelia Fermüller and Thomas Meigen (Freiburg). Thank you. I thank Professor Frank Bremmer (Marburg) as speaker of the Giessen/Marburg graduate program and the German Research Concil (NeuroAct 885/1) for its support. Biology students Florian Brüning, Andreas Mader, and Florian Leinenkugel (Freiburg, Germany) completed an internship under my supervision. They helped with data collection. Psychology student Anke Haberkamp (Giessen, Germany) also helped collecting data for a preliminary experiment. Thank you. My grandfather Heinrich Gleiß IV. implicitly lead me to the Vision Sciences. As a blind man he taught me to appreciate this astounding ability of vision and many more things. I am very thankful and I miss you. I am very much indepted to my parents, Elke und Rainer Hamburger, who supported me throughout my life without thinking about their own benefit. I thank you and I love you. Sven Hamburger, my older brother and sometimes my bad consciousness, gave me moral support, since he always pretends not to know what I am working on. Last but not least, I would like to say a heartily thank you to my fiancée Sandra. You put back your own interests in order to support me. You showed great tolerance for my long working hours and assisted me in any possible way. I hope I get a chance to give back at least a little bit. Thank you and I love you. v Zusammenfassung In den vergangenen Jahrhunderten haben Studien mit und über visuelle Illusionen zu einem besseren Verständnis des menschlichen visuellen Systems beigetragen. Ziel dieser Dissertation ist es nun, einen Beitrag zu diesem Forschungsgebiet mittels visueller Illusionen als Untersuchungsgegenstand zu leisten. In mehreren psychophysischen Experimenten und qualitativen Herangehensweisen habe ich versucht, dieses Ziel zu erreichen. Da es sich bei dem menschlichen visuellen System um ein überaus komplexes System handelt, dessen Verarbeitungsmechanismen sehr stark vernetzt und interaktiv sind, konzentriere ich mich in meiner Arbeit nicht ausschließlich auf ein einzelnes Forschungsgebiet bei visuellen Illusionen, sondern untersuche eine ganze Serie von Täuschungsphänomenen. Die vorliegende Dissertation ist in drei Hauptteile untergliedert: 1. Assimilationsphänomene und Filling-in (perzeptuelle Einfüllung); 2. geometrisch- optische Illusionen, Helligkeitsillusionen und Farbtäuschungen (diese werden unter Bedingungen mit Helligkeitskontrast und Isoluminanz – Helligkeitsgleichheit – mit chromatischem Kontrast untersucht); 3. Scheinbewegung in statischen Mustern. Diese Untersuchungen erweitern unser Wissen über verschiedenste Verarbeitungsmechanismen, beginnend bei den niedrigen Verarbeitungsstufen (Retina) bis hin zu den höheren Arealen im visuellen Kortex (V5/MT, MST). Die Untersuchungsergebnisse werden im Kontext aktueller Forschungsarbeiten im Bereich der Sehforschung interpretiert und diskutiert. Darüber hinaus präsentiere ich neuartige visuelle Phänomene (Illusionen), welche einen wertvollen Beitrag für zukünftige Forschung in den Bereichen Psychophysik, Physiologie und bildgebenden Verfahren zur Erforschung des Gehirns leisten können. vi Abstract Over the past centuries studies on visual illusions have provided us with a better understanding of the human visual system. The aim of this thesis is to contribute to this research field by utilizing visual illusions as research tools. In several psychophysical experiments and qualitative approaches I try to realize this aim. Since the human visual system is complex and processing mechanisms are highly interactive in networks, I will not focus on a single field but rather investigate a whole series of visual illusions. The thesis is divided into three major threads: 1. phenomena of fading and filling-in; 2. geometric-optical illusions, luminance illusions, and color illusions at conditions of luminance contrast and isoluminance with chromatic contrast; 3. apparent motion illusions. These studies expand our knowledge on various processing mechanisms from low-level (retina) to higher-levels of the visual cortex (V5/MT, MST). The results of the studies are interpreted and discussed within the context of current research work in the field of Vision Sciences. Furthermore, I present some new visual (illusory) phenomena, which could serve as valuable tools for future research in psychophysical, physiological, or brain imaging studies. vii Contents I Introduction 1 II Research work 9 Part 1 – Assimilation and filling-in 9 Chapter 1 – Color assimilation as a grouping factor 9 Chapter 2 – Filling-in with color: different modes of surface completion 25 Chapter 3 – Perceptual filling-in from the edge of the blind spot 53 Chapter 4 – Filling-in with texture: uniform vs. random orientation 70 Part 2 – Visual illusions at luminance contrast and isoluminance 103 Chapter 5 – Geometric-optical illusions at isoluminance 103 Chapter 6 – Weaves and the Herman grid 136 Chapter 7 – Grouping by contrast – figure-ground segregation is not fundamental 170 Part 3 – New insights from static motion illusions 181 Chapter 8 – Apparent rotation and jazzing in Leviant’s Enigma illusion 181 Chapter 9 – Reversal of apparent rotation in the Enigma figure with and without motion adaptation and the effect of T-junctions 206 Chapter 10 – A new motion illusion: the Rotating-Tilted-Lines illusion 229 III Conclusion 239 Erklärung Supplemental material (CD-ROM) viii “The complex structure of the visual system is sometimes exposed by its illusions.” D.M. Eagleman (2001, p920) I Introduction Visual Illusions and why we study them “The act of ‘seeing’ seems so effortless that it is difficult to appreciate the vastly sophisticated – and poorly understood – machinery that underlies the process” (Eagleman, 2001, p920). Visual illusions exist at the extremes of what our system has evolved to handle.