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Mariann Füzesiné Hudák UNDERSTANDING BASIC VISUAL

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Mariann Füzesiné Hudák UNDERSTANDING BASIC VISUAL Budapest University of Technology and Economics PhD School in Psychology – Cognitive Science Mariann Füzesiné Hudák UNDERSTANDING BASIC VISUAL MECHANISMS THROUGH VISUAL ILLUSIONS PhD Thesis Supervisor: Dr. Ilona Kovács Budapest, 2013 ‘There is no harm in doubt and skepticism, for it is through these that new discoveries are made.’ (Richard Feynman, Letter to Armando Garcia J, December 11, 1985) 1 Acknowledgements .......................................................................................................................... 3 2 Abstract ............................................................................................................................................ 4 3 Kivonat ............................................................................................................................................. 4 4 Summary .......................................................................................................................................... 4 5 Összefoglaló ..................................................................................................................................... 5 6 Introduction ...................................................................................................................................... 7 6.1 Looking into the ‘black box’ through illusions - An alternative to physiological studies ...... 7 6.2 Theories of lightness-brightness perception .......................................................................... 12 6.2.1 The roots ............................................................................................................................ 12 6.2.2 Lateral inhibition – the classical textbook explanation ..................................................... 14 6.2.3 Recent lateral inhibition-based models ............................................................................. 17 6.2.3.1 Filtering and symbolic description ............................................................................ 17 6.2.3.2 High-pass filtering ..................................................................................................... 18 6.2.3.3 Multiple-scale filtering – natural image statistics ...................................................... 19 6.2.3.4 Multiple-scale filtering – the oriented DoG model ................................................... 21 6.2.4 Mid-level theories: Intrinsic image models ....................................................................... 24 6.2.5 Mid-level theories: Anchoring .......................................................................................... 30 6.2.5.1 The original anchoring theory ................................................................................... 30 6.2.5.2 Double anchoring theory ........................................................................................... 37 6.2.6 A low-level alternative: activation spreading alias filling-in ............................................ 40 6.2.7 Filling-in brightness modelling vs. anchoring: not mutually excluding concepts ............. 55 2 6.3 Chromatic illusions – the potential application of a good brightness model to chromatic stimuli 58 6.4 Dynamic illusions .................................................................................................................. 62 6.4.1 Dynamic illusions elicited by static images: where filling-in gets confused ..................... 62 6.4.1.1 The Scintillating grid illusion .................................................................................... 62 6.4.1.2 Kitaoka’s induced movement illusions ..................................................................... 65 6.4.1.3 Stabilized retinal images............................................................................................ 67 6.4.2 Afterimages elicited by short presentation: the temporal dynamics of filling-in vs. adaptation ....................................................................................................................................... 68 6.4.3 Adaptation and temporal integration ................................................................................. 72 6.4.4 A dynamic illusion for the two eyes: binocular rivalry and the role of adaptation in it .... 73 6.5 Developmental aspects of visual illusions ............................................................................. 76 7 The aims and synopses of the thesis .............................................................................................. 81 8 References ...................................................................................................................................... 86 6. Studies…………………………………………………………………………………......95 6.1 Study I.….……………………………………………………………………………......95 6.2. Study II………………………………………………………………………………….109 6.3. Study III………………………………………………………………………………...118 6.4. Study IV………………………………………………………………………………...122 1 Acknowledgements I would like to thank my supervisor, Ilona Kovács for guiding me during my work on this thesis and during the years as her student at the PhD school. I am very grateful to János Geier, with whom I have been working together since my undergraduate years and who has been supporting me both as an advisor, colleague and as a friend. His generous help in teaching me computer programming and many other skills that a good scientist needs is also invaluable. I am also indebted to my co-authors with whom I have worked during the years, Stuart Anstis, Jochen Braun, Björn Friedrich, Patrícia Gerván, Zoltán Jakab, Bernd Lingelbach and Alexander Pastukhov. I also would like to thank Orsolya Jánosházi and Nóra Szelényi for their comments on earlier drafts of this work, and all observers for participating in our experiments. 3 2 Abstract The aim of my research is to investigate basic visual mechanisms by means of various visual illusions. The main focus is on brightness perception, where we tested the plausibility of several models, including a long-standing textbook explanation, by varying the physical characteristics of images eliciting brightness illusions and comparing the resulting perceptual experience with the predictions of the models. We refuted the textbook explanation of classical illusions and supported the filling-in approach of brightness modelling. We also investigated the temporal integration of monocular and binocular vision by means of dynamic illusions, after-effects and binocular rivalry. In the latter case, developmental changes were also found. 3 Kivonat Kutatásom célja a látás alapfolyamatainak megismerése különféle vizuális illúziók segítségével. A leghangsúlyosabb ezek közül a világosságészlelés, amelynek számos modelljét teszteltük, beleértve a régóta elfogadott tankönyvi magyarázatot is. Ehhez a világosságillúziókat kiváltó képek paramétereit variáltuk, és összehasonlítottuk a modellek jóslatait az emberek által észlelt világosságprofillal. Így klasszikus illúziók tankönyvi magyarázatát cáfoltuk meg. Eredményeink a kitöltés alapú modelleket támasztják alá. Dinamikus illúziók, utóképek és a binokuláris rivalizáció jelenségének segítségével a látórendszer téri integrációját is vizsgáltuk, mind az egyszemes, mind a két szemmel történő látás esetén. Utóbbi esetben a fejlődés során fellépő változásokat is találtunk. 4 Summary Visual illusions provide ample opportunities to investigate the basic working mechanisms of the visual system. Such illusions, in which the perceived pattern of light differs from its physical distribution, are systematic “errors” produced by normal visual information processing. If the overall pattern of errors are systematically mapped by psychophysical methods and captured by a single unified explanatory theory in the particular domain (such as brightness or colour), then that theory is likely to account for veridical perception as well, since the pattern of errors indicate how the underlying mechanism works. Our first goal was to investigate whether the generally accepted explanation of numerous lightness-brightness phenomena, the concept of lateral inhibition was indeed suitable to 4 explain classical brightness illusions. For this aim, we used the two textbook strongholds of this long-standing theory. First, we curved the Hermann grid, which eliminated the illusory spots. Second, we modified the background of the Chevreul staircase, which significantly altered the illusion. In both cases, the conditions of the lateral inhibition-based explanation remained untouched. Therefore, it failed to predict the elicited perceptual changes. On this basis, we rejected lateral inhibition as an explanatory principle for brightness phenomena. In the introduction, the limitations of current theories, including low-level filtering models and mid-level theories are also analysed and probed with modifications of illusions they are supposed to account for. Our second goal was to find a unified explanation for the investigated brightness phenomena. We showed that edges played a crucial role in brightness perception. In the Hermann grid, the illusion persisted if one side of the streets remained straight. In the Chevreul illusion, we found that the change of the upper and lower boundary edges of the staircase caused the perceptual changes. Other data from the literature are also reviewed, proving that the most important factor in brightness and colour perception is the edge-structure of the image, and homogeneous surfaces are filled-in based on the signals originating from edges. Besides
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