Textbook Notes (368,192)
Canada (161,707)
Psychology (9,695)
PSYB65H3 (479)
Chapter 13&14

Chapters 13 & 14

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Zachariah Campbell

Chapter 13 The Occipital LobesThe Autonomy of the Occipital LobesThe occipital lobes form the posterior pole of the cerebral hemispheres lying beneath the occipital bone at the back of the skull On the medial surface of each hemisphere the occipital lobe is distinguished from the parietal lobe by the parietal occipital sulcusWithin the visual cortex however are three clear landmarks The most prominent is the calcarine sulcus which contains much of the primary cortex The calcarine sulcus divides the upper and lower halves of the visual world On the ventral surface of each hemisphere are two gyri lingual and fusiform The lingual gyrus includes part of visual cortical regions V2 and VP whereas V4 is in the fusiform gyrusSubdivisions of the Occipital CortexThe discovery that area V1 is functionally heterogeneous that a given cortical area may have more than one distinct function was unexpected Area V2 also is heterogeneous when stained with cytochrome oxidase but instead of blobs stripes are revealed Because of the distinct stripes the visual cortex is sometimes called the striate cortexThe distribution of color function across much of the occipital cortex and beyondthat is areas V1 V2 V4 V8 is important because until recently the perception of form or movement was believed to be color blind It has now become clear that color vision is integral to the analysis of position depth motion and the structure of objects Connections of the Visual CortexV1 the striate cortex is the primary vision area it receives the largest input from the lateral geniculate nucleus of the thalamus and it projects to all other occipital regions V1 is the first processing level in the hierarchyV2 also projects to all other occipital regions V2 is the second level After V2 three distinct parallel pathways emerge en route to the parietal cortex superior temporal sulcus STS and inferior temporal cortex for further processingThe parietal pathway or dorsal stream has a role in the visual guidance of movement and the inferior temporal pathway or ventral stream is concerned with object perception including color The middle pathway along the superior temporal sulcus the STS stream is probably important in visuospatial functions and in the perception of certain types of movementsA Theory of Occipital Lobe Function In a sense areas V1 and V2 appear to serve as mailboxes into which different types of information are assembled before being sent on to the more specialized visual areasIt is not surprising to discover that selective lesions up the hierarchy in areas V3 V4 and V5 produce specific deficits in visual processing People who suffer damage to area V4 are able to see only in shades of gray Curiously patients not only fail to perceive colors but also fail to recall colors perceived before their injuries or even to imagine colors In a real sense the loss of area V4 results in the loss of color cognition or the ability to think about colorSimilarly a lesion in area V5 produces an inability to perceive objects in motion Objects at rest are perceived but when the objects begin to move they vanish In principle a lesion in area V3 will affect form perception but because area V4 also processes form a rather large lesion of both V3 and V4 would be required to eliminate form perceptionPeople with V1 lesions seem not to be aware of visual input and can be shown to retain some aspects of vision only by special
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