PSYC 3380 Cognitive Neuroscience Vision PDF

PSYC 3380 – Cognitive Neuroscience Vision Lecturer: Ezgi Palaz, MSc Sensation & Perception Sensation: Effects of stimulus on sensory organs Perception: Interpretation of stimulus based on prior experience. Brain does not merely interpret the real image, but is involved wi...

PSYC 3380 – Cognitive Neuroscience Vision Lecturer: Ezgi Palaz, MSc Sensation & Perception Sensation: Effects of stimulus on sensory organs Perception: Interpretation of stimulus based on prior experience. Brain does not merely interpret the real image, but is involved with active construction of the visual representation of the world. From Eye to Brain From Eye to Brain Rod cells are specialized for low intensity of light and movement Cone cells are specialized for high intensity of light → color info Fovea is entirely made of cones → visual acuity. Blind spot is where the optic nerve leaves the eye. Geniculostriate Pathway Optic nerve Optic chiasm Optic tract Lateral Geniculate Nucleus (LGN) Primary visual cortex (V1) Primary Visual Cortex (V1) Occipital lobe, at the posterior of the brain is responsible for visual processing. V1 is the first stage of processing in the cortex. Hubel & Wiesel – single cell recordings in cats: Hubel and Wiesel Cat Experiment (youtube.com) Primary Visual Cortex (V1) Simple cells: Respond to particular orientation and single points of light Complex cells: Combination of simple cells, larger receptive fields, respond to movement of orientation, do not respond to single points of lights Hypercomplex cells: Just outside V1, built from responses of complex cells, respond to orientation and length THESE CELLS ENABLE V1 TO CONSTRUCT COMPLEX VISUAL INFORMATION FROM SIMPLE INFORMATION Cortical & Non-Cortical Routes ~10 pathways discovered Geniculostriate pathway is the best understood and make largest contribution to human visual perception Other routes are evolutionary older ◦ Pathway to suprachiasmatic nucleus in the hypothalamus provides information about time of day ◦ Pathways via superior colliculus and inferior pulvinar are important for orienting stimuli Problems with Primary Visual Cortex Retinotopic organization: Layout of the receptive fields of neurons in V1 reflect the spatial organization of the retina. Hemianopia: Cortical blindness restricted to one half of the visual field (associated with damage to the primary visual cortex in one hemisphere). Quadrantanopia: Cortical blindness restricted to a quarter of the visual field. Scotoma: A small region of cortical blindness How do they see? Blindsight Inability to report perceiving visual stimulus even though performance suggests otherwise. *conscious vs unconscious routes* Case of DB – he reported not seeing stimuli but oriented his eyes correctly toward stimuli ◦ Could detect orientation, motion, contrast Blindsight (youtube.com) Blindsight - Blind man can see and avoid obstacles (youtube.com) Extrastriate Areas in Vision Extrastriate Areas in Vision V4: A region of extrastriate cortex associated with color perception and color constancy (color of a surface is perceived as constant even when illuminated in different lighting conditions). Achromatopsia: A failure to perceive color due to damage to V4 (the world appears in grayscale). It’s not the same as color blindness (deficient or absence of types of cone cells) Extrastriate Areas in Vision V5 (or MT): A region of extrastriate cortex associated with motion perception. Akinetopsia: A failure to perceive visual motion due to damage to V5. Case of LM – cannot detect direction of movement but can detect biological motion Dual Stream Visual Processing Object Recognition 1) perception of basic elements (e.g., edges of various lengths, contrasts & orientations) 2) grouping physical elements (depth cues and divide surfaces) 3) the viewer-centered description is then matched onto stored 3D descriptions of the structure of objects ◦ structural descriptions: memory of the 3D representation of an object ◦ object constancy: an understanding that objects remain the same irrespective of differences in viewing condition (Viewpoint invariance) 4) meaning is attributed to the stimulus Model of Object Recognition Agnosia Failure in object recognition Apperceptive agnosia: A failure to recognize objects due to a deficit at the level of object perception (stage 2). Associative agnosia: A failure to recognize objects due to a deficit at the level of semantic memory (stage 3 and 4). Apperceptive Agnosia Case of HJA (stroke patient): seeing the part but not the whole Apperceptive Agnosia Case of HJA: impaired at deciding if objects are real or made up and naming objects. However, he can copy drawings and draw objects from memory Associative Agnosia Inability to recognize an object or orientation of object Categorical Perception Category specificity: The notion that the brain represents different categories in different ways (and/or different regions). Parahippocampal place area (PPA): area of the brain that responds to scenes more than objects The extrastriate body area (EBA): area of the brain that responds to the human body more than to faces, scenes or objects Face Recognition Face Recognition Fusiform face area (FFA): An area in the inferior temporal lobes that responds more to faces than other visual objects. Prosopagnosia: inability to recognize previously familiar faces. Occipital Face Area (OFA): responds to individual face parts Amygdala (AG): activated by emotional aspects of faces Superior Temporal Tulcus (STS): responds to where the person is looking and to mouth movements, dynamic aspect of faces (such as expression, and lip and gaze movements) Frontal Cortex (FC): responds to facial attractiveness The model of face recognition FFA and STS in the brain FFA STS and OFA in fMRI Visual expertise with faces Gauthier et al. (1999) Two parts to the expertise hypothesis: 1. faces require discrimination within a category (between one face and another) 2. we become “visual experts” at making these fine within-category distinctions due to prolonged experience with thousands of faces Vision «Imagined»