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PSYC 2240 - Test 2 Notes (Fall 2011)

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York University
PSYC 2240
Pauline Charlton

PSYC 2240Test 2 Notes Chapter 6 Vision The Law of Specific Nerve Energies activity by a particular nerve always conveys the same type of information to the brain Sensory coding is determined by which neurons are active Whatever excites a particular nerve establishes a special kind of energy unique to that nerve The strength of a stimulus determines the amount of a receptor cells depolarization or hyperpolarization Rene Descartes believed that the brains representation of a stimulus resembled the stimulusVisual receptors send messages to bipolar cells and in turn send its message as motor neurons to the ganglion cells which also deals with spontaneous photoreceptors and fire action potentials to the rods and conesThe axons of ganglion cells form the optic nerve that connects to the brain The exit of the eye that contains blood vessels and no receptors is the blind spotAmacrine cells function as additional cells that receive information from bipolar cells and send it elsewhere other bipolar cells ganglion or another amacrine cells They control the ability of the ganglion cells to respond to shapes movements or other visual stimuli Many ganglion cells go to the lateral geniculate nucleus in the thalamus occipital cortex The macula is the center of the human retina and the central portion is the fovea where acute and detailed vision takes place due to tightlypacked receptors and no ganglions o The ganglion cells in the fovea are called midget ganglion cells Visual ReceptorsRods are more concentrated outside the fovea and deals with dim light and night visionCones are more concentrated in the fovea and deals with bright light and color pigments o Rods outnumber cones 201 but cones provide 90 of the brains input o Rods and cones both contain photopigments chemicals that release energy when struck by light When rods are exposed to bright light they are bleachedHorizontal cells make inhibitory contact onto bipolar cells which in turn make synapses onto amacrine and ganglion cells Sight is less developed in the womb and becomes more developed after birthBrain is capable of remolding itself plasticity Eyes can adapt to new experiencesProsopagnosia is the inability to recognize faces while visual agnosia is the inability torecognize objects in general despite both disorders having adequate visionary sightArrangement of visual receptors in the eye is highly adaptive to the environment Trichromatic YoungHelmholtz theory three different types of color perception through the relative rates of response of cones light versus pigments and long versus short wave conesHumans can only perceive visible color wavelengths between 400 and 700 Opponentprocess theory we perceive color in terms of paired opposites of differentwavelength cones Retinas periphery argues that the scarcity of cones results in nonuseful color visionThe brain has a mechanism that perceives color on a continuum Retinex theory cortex compares information from various parts of the retina to determine the brightness and color for each area Color Consistency recognizing color regardless of lighting Afterimages negative color replacement of redgreen yellowblue whiteblack Color vision deficiencyColor blindness redgreen yellowblue and rarely whiteblack Processing in the Retina The connections in the visual cortex are reciprocal Ventral stream magnocellular visualpath in temporal cortex specializes in identification and recognition while dorsal stream parietal cortex specializes in the motor applications
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