Perception lecture 1.3.pdf

Foundations of Perception and Cognition Spatial vision Dr Deanne Green  We acknowledge and pay our respects to the Kaurna people, the traditional custodians whose ancestral lands we gather on. We acknowledge the deep feelings of attachment and relationship of the Kaurna people to country a...

Foundations of Perception and Cognition Spatial vision Dr Deanne Green  We acknowledge and pay our respects to the Kaurna people, the traditional custodians whose ancestral lands we gather on. We acknowledge the deep feelings of attachment and relationship of the Kaurna people to country and we respect and value their past, present and ongoing connection to the land and cultural beliefs. Perception Lectures What will you learn 1. Intro to sensation and perception 2. Methods 3. Spatial vision 4. Body senses 5. Depth perception 6. Motion perception Spatial vision Classification of the senses Sense Sensation Receptor Sensory Cortex Structure Vision Electromagnetic Photoreceptors Eyes Primary Visual energy Cortex Hearing Air pressure Mechanoreceptors Ears Auditory Cortex waves Touch Tissue distortion Mechanoreceptors Skin, Muscle Somatosensory Thermoreceptors Cortex Taste/Smell Chemical Chemoreceptors Nose/Mouth Taste and Olfactory Cortex Balance Fluid movement Mechanoreceptors Vestibular Temporal Cortex organs Some history Part 1 Marr’s model of vision Marr’s model of vision Visual processing passes through a series of stages: Ø Primal sketch Ø 2.5D (2D with illusion of depth) sketch Ø 3D sketch Marr’s model of vision Input image Primal sketch 2.5D sketch 3D sketch Marr’s ideas Hugely influential Perhaps not strictly correct, but still a very useful conceptual structure Beginning of computational neuroscience Part 2 Hierarchical stages of sensory processing  Primary visual cortex (V1) There are two distinct classes of cells in the primary visual cortex (V1): simple cells and complex cells. One defining feature of complex cells is their spatial phase invariance; they respond strongly to oriented grating stimuli with a preferred orientation but with a wide range of spatial phases. In simple cells the responses are periodic, whereas in complex cells they are steady in time Orientation tuning in simple and complex cells The leftmost column shows bar stimuli at different orientations and positions, superimposed on a simple cell receptive field (top) and a complex cell receptive field (bottom). The trace adjacent to each stimulus shows neural activity as a function of time. The thick horizontal bars mark the duration of each stimulus. Contrast sensitivity Part 2 Review of eye anatomy Sensitivity Contrast sensitivity Effects on sight Distribution of rods and cones Wadsworth, 2002 Snellen eye chart Humans are not equally sensitive to all contrasts Human contrast sensitivity for different spatial frequencies Human contrast sensitivity function Judging distance Describing size Actual size and retinal size Judging distance Convergence (talk about in lecture 5) Size Texture gradients Judging distance Shape representation Part 3 Making inferences Shape representation Gestalt laws Design principles Bottom-up and Top-down processing Shape representation Shape representation Shape representation Shape representation Shape representation We make inferences based on Ø Past experience Ø Categorisation Ø Gestalt laws Gestalt Laws Proximity Similarity Continuity Common fate Closure Proximity Proximity Similarity Continuity Y A B X Continuity Y A B X Common fate Closure Closure Bottom-up processing Bottom up processing; stimuli goes into senses, and we allow the stimulus itself to shape our perception, without any preconceived ideas Ø Driven by senses Ø Allows us to see shapes, infer meaning Ø E.g., gestalt laws Top-down processing Top-down processing; we use our background knowledge and expectations to interpret what we see Ø Driven by knowledge and experience Ø Cognitive (not sensory) Ø E.g., Stroop effect Red Green Red Blue Purple Window Special visual processing Part 4 Pareidolia Special visual processing Category specific regions Deficits Face Pareidolia Face Pareidolia Face Pareidolia Face Pareidolia Face Pareidolia Face Pareidolia Category Specific Visual Areas objects faces places With thanks to Culham Lab Deficits in face processing Prosopagnosia Inability to recognise faces (face blindness) Acquired or congenital Acquired as a result of brain trauma, stroke or degenerative disease Capgras syndrome Inability to recognise the identity of a person Acquired as a result of brain trauma, stroke or degenerative disease Acquired or congenital What is happening in the following illusions? Using what we learnt Part 5 Demystifying visual illusions Using what we learnt Gestalt Laws Proximity Similarity Continuity Common fate Closure Summary References Mather, G. (2016): Foundations of perception Psychology Press Ltd., Hove Chapters 9 & 10 Snowden, R., Thompson, P & Troscianko, T (2006): Basic Vision Oxford University Press, Oxford. Chapters 4 & 10 Ashida, H., Kuriki, I., Murakami, I., Hisakata, R., & Kitaoka, A. (2012). Direction-specific fMRI adaptation reveals the visual cortical network underlying the “Rotating Snakes” illusion. Neuroimage, 61(4), 1143-1152