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PSYC 212 (49)
Chapter 10

Chapter 10.doc

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Department
Psychology
Course
PSYC 212
Professor
Remy Allard
Semester
Fall

Description
Chapter 10 The Visual System Cortical Processing and Object PerceptionVisual cortexa general term given to the collection of cortical areas that are involved in processing visual informationvisual information processed in occipital lobe in two pathwaysodorsal streamproceeds into parietal lobe where neural structures primarily involved in dynamicspatial aspects of vision motion perception spatial orientation visuomotor behaviouroventral streamproceeds into temporal lobe where neural structures primarily involved with encoding structural details of visual image leading to complete representation of various object classesA The Retinal Projection to the BrainRenaissance started correct understanding of retinal projection to the brainAndreas Vesalius of Padua and for next 3 centuriesFusion of two optic nerves has impact on projection pattern of retinal fibreshow brain analyzes visual environment1 General Layout of the Retinal ProjectionRetinal nerve fibres emerging form eyeball quickly become myelinated to provide maximum insulation for electrical signals being conducted from themVast majority of signals have to travel several centimeters before arriving at next neural structure for further processingSubcortical structuresthe part of the brain that resides below the cortexSubcortical targets of the retinal output oInterior part of brain largely made of 2 componentswhite matter nerve fibres carrying signals for the various sensory and motor systemsneuron clusters that vary from very small to largewell organized thalamusoThalamusmajor site for relay of sensory information oVisual system has on each side of the brain major thalamic structure lateral geniculate mucleus LGNPrinciple subcortical target of retinal projectionplays critical role in transfer of visual information of visual cortexSuperior colliculuspaired structure sitting just below LGN close to midline of the brainCortical projection of retinal signalsoRetinal signals reach visual cortex after theyve passed through LGNoRetinal fibres synapse onto LGN neurons so axons carry visual signals to cortexoOptic radiationmassive fibre projection that transmits LGN signals to visual cortex in occipital lobe with no crossover of fibres therefore right and left LGN project on their respective sidesSignal splitting at optic chiasmoCrossover takes place somewhere along fibre pathway so right side of the brain samples sensory information from left side of the body vice versaoRetina divided into temporal and nasal halffovea serving as midpointoEach optic nerve contains axons from all ganglion cells in eyeWhen two optic nerves come together at optic chiasm the point at which the two optic nerves fuse together and at which a partial set of retinal fibres cross over to the opposite sideAxons from all ganglion cells in temporal half of retina project to LGN on same sideNasal fibres cross over and project to opposite side of LGNoOptic nerve carries retinal fibres from only one eyeFibre bundle emerging from the optic chaism contains fibres from both sideTemporal fibres are ipsilateral an anatomical structure on the same side of the bodyNasal fibres arecontralateral an anatomical structure on the opposite side of the bodyNerve bundle called optic tract the nerve bundle beyond the optic chiasm containing retinal fibres from both eyesFibres terminate in LGN on same sideoReason our eyes flip things and switchour eyes fixate on particular objects so that it image is on the fovea of the eyesThe fixated object defines the centre of our visual field and things on the left define the left visual field things on the right define the right visual fieldSignal splitting at optic chiasm causes optic tract to carry information from only onehalf of the retina of each eyeRight optic tract transmits signals from the right retinal halves of each eyeLeft optic tract transmits signals from the left retinal halvesoLeftright transformation meaning that all objects in left part of visual world imaged on right half of each retinaEach optic tract transmits visual information that represents the oppositecontralateral half of the visual fieldOptic tract signals transmitted to LGN then directly to visual cortexThe foveal representationoLeftright crossover of visual information implies neural signals form voeal retina should theoretically become split down the middleoRequires precise anatomical partitioning of left and right retinal fields a portion of the retinal surfaceoGanglion cells reside immediately on either side of the midline that follows appropriate course according to projection rules through optic chiasmoNo precise boundariesoProjection pattern along entire vertical midline through foveafuzzyoSome of ganglion cells within fuzzy zone project along ipsilateral pathway
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