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PSYB65H3 (519)

Occipital Lobes

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Zachariah Campbell

Lecture 9 Occipital Lobes Subdivisions of the Occipital Cortex - Area V1 o Laminar (striped) organization most distinct of all cortical areas o Aka. Striate Cortex due to striped appearance - Color Vision o Primary job of V4, but distributed throughout occipital cortex Connections of the Visual Cortex - Connections o Primary Visual Cortex (V1)  Input from LGN  Output to all other levels o Secondary Visual Cortex (V2)  Output to all other levels o After V2  Output to parietal lobe – Dorsal Stream Lecture 9  Visual guidance of movements  Output to the inferior temporal lobe – Ventral Stream  Object perception o Able to associate object with a memory or label  Output to superior temporal sulcus (STS – STS Stream  Visuospatial functions (body-oriented) Theory of Occipital Lobe Function - Vision begins in V1 that is heterogeneous, & then travels to more specialized cortical zones - Selective lesions up the hierarchy produce specific visual deficits - Lesions to V1 are not aware of seeing Visual Functions Beyond the Occipital Lobe - Multiple visual regions in the temporal, parietal, & frontal lobes indicate there is sophisticated adaptation system and to act upon it - Vision o Not unitary, composed of many specific forms of processing o 5 categories for vision Categories of Vision - Vision for Action o Parietal Visual Areas in the Dorsal Stream o Reaching o Ducking o Catching - Visual Recognition o Temporal Lobes o Object Recognition  To associate it with a label - Visual Space o Parietal & Temporal Lobes o Spatial Location Lecture 9  Egocentric Space: Location of object relative to person  Allocentric Space: Location of an object relative to another object Imaging Studies of Dorsal & Ventral Streams - PET Study o Found activation for facial stimuli in the temporal region & activation during a location task in the posterior parietal region & frontal lobes o Detection of motion activated V5, while detection of shape activated STS o Color perception activated area V4 Disorders of the Visual Pathway - Monocular Blindness o Loss of sight in one eye o Results from destruction of retina or optic nerve Lecture 9 o Severely affect depth perception - Bitemporal Hemianopia o Loss of vision rom both temporal fields o Results from lesion to optic chiasm - Nasal Hemianopia o Loss of vision of one nasal field o Results from lesion of the lateral chiasm Slide 19 - Homonymous Hemianopia o Blindness of one entire visual field o Results from a complete cut of the optic tract o LGN or V1 - Macular Spring o Sparing of the central or macular region of the visual field o Results from a lesion to the occipital lobe - Quadrantoanopia or hemianopia o Complete loss of vision in ¼ of the fovea or in ½ of the fovea o Results form a lesion to occipital lobe - Field Defects o Somatomas – small blind spots o Results from small lesions to occipital lobe - Object Agnosia o Apperceptive Agnosia  Deficit in ability to develop a percept of the structure of an object/objects  Simultagnosia  Unable to perceive more than one object at a time o Results from bilateral damage to the lateral parts of the occipital lobes - Assoctiave Agnosia o Can perceive objects, but cannot identify them Lecture 9 o Results from lesions to anterior temporal lobes - Prosopagnosia o Cannot recognize faces (identity) o Can recognize facial features, facial expressions, & tell human from nonhuman faces - Alexia o Inability to read o Form of object agnosia – inability to construct perceptual wholes from parts o Form of associative agnosia – word memory is damaged or inaccessible  Cannot associate word with perceptual image o Results from damage to
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