Visual Perception and Visual Illusions Lecture PDF

Visual Perception and Visual Illusions Radoslaw Wincza [email protected]  Week 4 – Visual Perception and Visual Illusions Radek Week 7 – Individual Differences and Visual Illusions (essay ’s relevant) content Week 8 – Psychology o...

Visual Perception and Visual Illusions Radoslaw Wincza [email protected]  Week 4 – Visual Perception and Visual Illusions Radek Week 7 – Individual Differences and Visual Illusions (essay ’s relevant) content Week 8 – Psychology of Magic Week 9 – Individual Differences in Susceptibility to Magic (essay relevant)   What is visual perception?  Gestalt Laws  Context sensitivity  Visual illusions Overview  History of visual illusions  Types of visual illusions  Some common explanations  Conclusions What is visual perception? Visual Perception Starts at the retina Most of processing of visual stimuli happens in the occipital lobe Two pathways Vision for action (dorsal stream) Vision for perception (ventral stream) Home to the primary visual cortext (V1) – shape recognition Other V-areas too V2 – Integration and processing of visual information V3 – Motion / colour V4 – Colour V5 – Motion See Schiller & Tehovnik (2015) Gestal t Laws   Started around 1912 with Max Wertheimer and remained What is influential until approximately Gestalt 1950/1960  Provides a framework to psycholog understand perceptual y? organisation (Wagemans et al. 2012)  The whole is more than the sum of its parts Gestalt Laws Explained  How we organise what we see into patterns  Also, the Law of Common Fate – things moving in the same direction are grouped together  Things are not perceived in isolation 9/3/20XX Presentation Title 9  Law of Continuity Law of Closure  What is context sensitivity? Context Sensitivity – What Is it? The ability to integrate Central to cognition and numerous elements of the visual perception (Doherty et al., 2008) scene (Kaldy & Kovacs, 2004) Two broad styles of sensitivity Field-independent Field-dependent - Local - Global - Focused on - Seeing the forest details before the trees - Seeing the trees - Top-down before the forest processing - Bottom-up processing Bottom-up versus Top-down Bottom-up Top-down Stimulus-driven Memory Raw sensory data (e.g., shape, Knowledge colour, edges) Expectations More automatic Perceptual experiences (Eysenck, 1998) Can perception be understood without cognition? (Vetter & Newen, 2014)  So, which one is less context- sensitive? Field-Independent or Field-Dependent How context- sensitive are you? Instructions  Try not to think too much over what you see  Do not use your fingers  Make a guess if unsure Let’s find out! Scan the below QR code. My prediction Most answers clustred around 8 + / - 3 My score... Replication of Phillips et. (2004) Will we observe any gender differences? If so – in what direction? Come back in Week 7! So, what would high or low scores indicate? Consider Sarah and Tom Sarah likes to have a broad While Tom likes to focus on the perspective details Better accuracy on a visual illusion task would indicate greater influence of bottom-up processes, so field- So what are visual illusions? Two explanations They occur when our perception departs from the physical properties of the stimulus (Wincza et al. 2024). What we perceive is not what is really there. Also, cognitively impenetrable (Todorović, 2020) – you cannot unsee them even though you know how they work! Is it a form of hallucination? Put simply – no. Being susceptible to visual illusions is normal. Although visual illusions in health research have similar effects as the visual illusions covered here (Sasaki et al., 2022) Usually experienced in neurodegenerative disorders such as Parkinson’s disorder Short history of visual illusions Is it a new phenomena? The study of visual illusions is as old as psychology as a discipline (Wade et al., 2007). The first empirical investigation was conducted in 1855 on the Oppel- Kundt illusion (Coren & Girgus, 1978). Many of the visual illusions covered in this lecture have been discovered around 1900. Many early influential psychologists such as Herman Ebbinghaus (known for his forgetting curve) or Alfred Binet (known for his IQ scale). Illusions are all around us Consider these examples The Banana Illusion The Pint Glass Illusion The Chicken-Church Illusion (pareidolia) Types of Visual Illusions Gregory (1997) suggests: *Note motion illusions are not Included Today, we will focus on distortions. Ambiguities The Duck-Rabbit Figure, the Necker Cube, the Old- Young Woman Although Todorović (2020) argues these are not visual illlusions Paradoxes Fictions And lastly distortions* Incorrect perception of stimulus’ physical properties (Wincza et al. 2024) Arguably the most numerous group Mutliple sub-groups exsists such as: Colour (e.g., the Adelson’s Checkerboard Illusion) Size (e.g. the Ebbinghaus, Ponzo, Muller-Lyer illusions) Orientation (e.g. the Zollner illusion) *My favorite ones! Distortions explained Vertical Bias / Bisection Bias (Kunnapass, 1955) Context integration (Kaldy & Kovacs, 2003) Perceptual Rescaling / Size Constancy (Gregory, 1963)  Size constancy Size constancy The retinal image is identical, however, the brain compensates for the depth cues, hence distorting our perception – making things larger than they seem Objects would shrink and grow depending on their distance – distance judging would be very difficult Important for all everyday tasks For a review see Sperandio & Chouinard (2015) Colour constancy Colour constancy What would happen The brain compensates for without it? the changes in illumination Objects would appears as if (lighting conditions) they are lit by pure white Snowflakes will appear as light white in both the moonlight and sunlight Important for object recognition For a short review see Hulrbert (2007) Distortions of colour Simultaneous Brightness Illusion Adelson’s Checkerboard Illusion The Ponzo Illusion Distortions of orientation The Tilt Illusion The Zollner The Cafe Wall Illusion Illusion And many others... But there is much more... 41  So, what do visual illusion tell us about visual perception? Well, let’s go down memory lane Perceptual organisation Gestal laws Size and colour constancy Context integration How contextual information is processed by the visual system The role of bottom-up and top-down influences Differences in context sensitivity as a result of individual differences* *You will have to attend my next lecture in three weeks to find more about it! Take home messages  Visual perception is far from accurate  Visual illusions are studied for over 150 years  Numerous types of visual illusion distorting size, colour, orientation...  Visual illusions offer a unique window into the study of human perception  Visual illusions are linked to context integration and pictorial depth perception as well as size and colour constancy References Anstis, S. 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