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Chapter 6 the Seeing Brain 5707 Brain and Cognitive Science Chapter 6 The Seeing Brain March 24, 2016 Introducing Brain and Cognitive Science Introducing the brain The Electrophysiological Brain The Imaged Brain The Lesioned Brain The Seeing Brain The Speaking Brain The Spatial Brain The Literate Brain The Acting Brain The Numerate The Remembering Brain The Executive Brain The Hearing Brain The Social & Emotional Brain 2 國立交通大學生物科技系暨研究所 黃植懋老師 1 Outline for today • From eye to the brain Anatomy of the eye Occipital lobe: cortical visual areas: V1, V2‐V4, MT • Deficit in visual perception V1: “blindsight” V4, MT • Objects recognition Variability in sensory information Two cortical pathways for visual perception • Face recognition • Encoding vs. decoding 3 4 國立交通大學生物科技系暨研究所 黃植懋老師 2 Amazing mind‐bending optical illusions https://www.youtube.com/watch?v=q9fcaHciF_o 5 Sensation and perception • Sensation The effects of a stimulus on the sensory organs Audition, olfaction, vision, etc. • Perception The elaboration and interpretation of a sensory stimulus based on, for example, knowledge of how objects are structured Olfactory perception, Gustatory (taste), somatosensory perception, visual perception, etc. 6 國立交通大學生物科技系暨研究所 黃植懋老師 3 7 Outline for today • From eye to the brain Anatomy of the eye Occipital lobe: cortical visual areas: V1, V2‐V4, MT • Deficit in visual perception V1: “blindsight” V4, MT • Objects recognition Variability in sensory information Two cortical pathways for visual perception Failure in object recognition • Face recognition • Encoding vs. decoding 8 國立交通大學生物科技系暨研究所 黃植懋老師 4 A Journey through the human eye https://www.youtube.com/watch?v=gvozcv8pS3c 9 Anatomy of the eye 10 國立交通大學生物科技系暨研究所 黃植懋老師 5 Anatomy of the eye 11 Demonstrating the blind regions of your eye 12 國立交通大學生物科技系暨研究所 黃植懋老師 6 Retina and photoreceptors of the eye • Two types of photoreceptors: rod and cone • Spatial representation: Foveal vision (mostly cones) High acuity Color vision Day vision Peripheral vision (mostly rods) Low acuity Black and white vision Night vision 13 Retina and photoreceptors of the eye • Two types of photoreceptors: rod and cone • Spectral sensitivity functions for rods and 3 types of cones: 14 國立交通大學生物科技系暨研究所 黃植懋老師 7 From the eye to the brain • Visual field: Left visual field is projected to right hemisphere Right visual field is projected to left hemisphere Visual information 90% via lateral geniculate nucleus (LGN) 10% via pulvinar nucleus & superior colliculus 15 From the eye to the brain Inferior view of the human brain 16 國立交通大學生物科技系暨研究所 黃植懋老師 8 Outline for today • From eye to the brain Anatomy of the eye Occipital lobe: cortical visual areas: V1, V2‐V4, MT • Deficit in visual perception V1: “blindsight” V4, MT • Objects recognition Variability in sensory information Two cortical pathways for visual perception • Face recognition • Encoding vs. decoding 17 Occipital lobe: cortical visual areas • Striate cortex + extrastriate cortex Visual perception Visual recognition • Striate cortex: primary visual cortex (V1, BA17): primary area responsible for sight ‐recognition of size, color, light, motion, dimensions, etc. • Extrastriate cortex: “Out of striate” Interprets information acquired through the primary visual cortex 國立交通大學生物科技系暨研究所 黃植懋老師 9 Occipital lobe: cortical visual areas • Map of cortical areas: Microelectrodes inserted in cortical areas show many areas responding to visual stimuli (in monkeys) Labeled V1, V2, V3, V4, etc. Neurons in different areas are sensitive to different types of stimuli 19 Occipital lobe: cortical visual areas • Each visual area provides its own limited analysis • Processing is distributed and specialized 20 國立交通大學生物科技系暨研究所 黃植懋老師 10 Animal research • Single‐cell recording: Effects of stimuli/behavior on neural firing patterns Response properties of neurons Receptive field 21 Occipital lobe: cortical visual areas • A functional specialization of occipital visual areas V1 Optimal stimuli: bars, edges, directions, etc. Partial separation between eyes Receptive fields: small 22 國立交通大學生物科技系暨研究所 黃植懋老師 11 Occipital lobe: cortical visual areas • A functional specialization of occipital visual areas V2‐V4 (visual areas 2‐4) Optimal stimuli: Same as V1, plus moving bars Most neurons receive input from both eyes Receptive fields: progressively larger V4: color center of the brain 23 Occipital lobe: cortical visual areas • A functional specialization of occipital visual areas V5 (also called MT, border with temporal lobe) Movement center of the brain Optimal stimuli: Only sensitive to moving object Receptive fields: very big 24 國立交通大學生物科技系暨研究所 黃植懋老師 12 Occipital lobe: cortical visual areas • Response of an MT neuron to visual stimuli moving in different directions and at different speeds 25 Occipital lobe: cortical visual areas • Neuroimaging studies show that different cortical areas are activated by different stimulus dimensions Zeki (1993), PET study: stimuli varying in terms of static color patterns activate medial occipital areas (corresponding to V1‐V4) stimuli in which objects move around activate more lateral areas (corresponding to MT) 26 國立交通大學生物科技系暨研究所 黃植懋老師 13 Occipital lobe: cortical visual areas V4 MT V1 27 Occipital lobe: cortical visual areas • Retinotopic mapping 28 國立交通大學生物科技系暨研究所 黃植懋老師 14 Occipital lobe: cortical visual areas • Retinotopic map Lower portion of V1 represents info about the top half of visual space Map is distorted 29 Visual illusions • Our percepts are more closely related to neural activity in higher visual areas. Illusory motion: Color aftereffects: activation in area MT activation in area V4 30 國立交通大學生物科技系暨研究所 黃植懋老師 15 31 32 國立交通大學生物科技系暨研究所 黃植懋老師 16 33 Honda illusion https://www.youtube.com/watch?v=7PGXZ‐oc2‐g 34 國立交通大學生物科技系暨研究所 黃植懋老師 17 Outline for today • From eye to the brain Anatomy of the eye Occipital lobe: cortical visual areas: V1, V2‐V4, MT • Deficit in visual perception V1: “blindsight” V4, MT • Objects recognition Variability in sensory information Two cortical pathways for visual perception • Face recognition • Encoding vs. decoding 35 Deficits in visual perception • Deficits in color perception: 正常視覺 Dichromats: Red‐green color‐blind: medium/long wavelength missing Blue‐yellow color‐blind: 紅色盲 short wavelength missing Normal cortical visual areas 綠色盲 36 國立交通大學生物科技系暨研究所 黃植懋老師 18 Deficits in visual perception • Deficits in visual perception Cortical blindness and “blindsight” Lesions around V1 Hemianopia (half of visual field) Quadrantanopia (1/4) Scotoma (small region) 37 Blindsight https://www.youtube.com/watch?v=GwGmWqX0MnM 38 國立交通大學生物科技系暨研究所 黃植懋老師 19 補充教材 39 Deficits in visual perception • Deficits in color perception Achromatopsia (無色視覺) “a”: without, “chroma”: hue Lesions around V4 (color) area due to strokes and tumors 40 國立交通大學生物科技系暨研究所 黃植懋老師 20 Deficits in visual perception • Deficits in color perception Achromatopsia (無色視覺) Difficulty to identify different hue, but not brightness (reflectance) 41 Deficits in visual perception • Deficits in color perception Patient P.T.: has difficulty in recognizing Monet’s painting, but okay for Picasso’s painting. Why? 42 國立交通大學生物科技系暨研究所 黃植懋老師 21 Deficits in visual perception • Deficits in motion perception Akinetopsia (motion blindness) view the world as a series of snapshots Deficits in MT area 43 Deficits in visual perception • Akinetopsia (motion blindness) https://www.youtube.com/watch?v=B47Js1MtT4w 44 國立交通大學生物科技系暨研究所 黃植懋老師 22 Outline for today • From eye to the brain Anatomy of the eye Occipital lobe: cortical visual areas: V1, V2‐V4, MT • Deficit in visual perception V1: “blindsight” V4, MT • Objects recognition Variability in sensory information Two cortical pathways for visual perception • Face recognition • Encoding vs. decoding 45 Object recognition • Combining lower‐level features to object • Object recognition is more than linking features to form a coherent whole Σ(parts) =/= whole • Interface between perception and memory 46 國立交通大學生物科技系暨研究所 黃植懋老師 23 Variability in sensory information • Object constancy refers to our amazing ability to recognize an object presented in very different conditions • Object recognition must overcome three sources of variability in sensory information: Changes in view point Changes in illumination Partial occlusion 47 Visual illusion • Ames room 48 國立交通大學生物科技系暨研究所 黃植懋老師 24 Ames room illusion http://www.youtube.com/watch?v=gJhyu6nlGt8 49 Outline for today • From eye to the brain Anatomy of the eye Occipital lobe: cortical visual areas: V1, V2‐V4, MT • Deficit in visual perception V1: “blindsight” V4, MT • Objects recognition Variability in sensory information Two cortical pathways for visual perception • Face recognition • Encoding vs. decoding 50 國立交通大學生物科技系暨研究所 黃植懋老師 25 Two cortical pathways for visual perception • Two major outputs from occipital lobe Ventral pathway leads to temporal cortex “What” pathway Object recognition Dorsal pathway leads to parietal cortex “where” pathway Spatial analysis 51 In‐vivo neuroimaging in human: what‐where distinction • Matching task: Object and spatial discrimination Object discrimination: increased occipital/temporal blood flow Spatial discrimination: increased parietal blood flow where: spatial what: object 52 國立交通大學生物科技系暨研究所 黃植懋老師 26 Human brain lesion: what‐where distinction • Patient D.F. normal visual acuity Severe visual agnosia Unable to orient card into slot Could not recognize the orientation of 3D objects (What) Normal ability to
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