Quiz 4 Study Guide EXP320202 04 2012 11 03 00 Be able to label the parts of the human eye Photoreceptors Where are they located They are located in the retina Can you describe the differences between the two types Rods detect the amount of light shapes contrasts and cones detect color Where are the rods and cones more or less concentrated within the eye Cone distribution is uneven in retina densest in the fovea center of the retina In the fovea the distribution of M and L cones are highest therefore red and green can be seen more so than other in the central field of view In the periphery of the retina the distribution of the S cones are highest blue and rods are highly concentrated Understand and describe the mechanisms of visual transduction How photoreceptors become activated or inactivated with or without the presence of light Hint slides 23 and 24 of the peripheral color detection lecture When a photon if light is absorbed by a molecule of opsin it transfers its energy to the chromophore portion of the visual pigment molecule This results in a cascade of biochemical events that cause the inside of the photoreceptor to become more negative or hyperpolarized Hyperpolarization causes calcium channels to close reducing the amount of free calcium in a cell which reduces the amount of neurotransmitter glutamate to be released in the synaptic terminal Photoreceptor cells connect to horizontal cells and bipolar cells Bipolar cells in turn connect to amacrine cells and ganglion cells Visual fields Understand what side of the retina and cortex gets visual information from the different visual fields Be able to draw the way in which visual information is processed from the left and right visual fields Hint slides 25 and 28 of the peripheral color detection lecture Information from the left visual field stimulates what parts of the retina and travels to which side of the brain and vice versa the axons of the ganglion cells converge and leave the eye via the optic nerve About half the fibers in the optic nerve cross to the contralateral side of the brain at the optic chiasm After the optic chaism visual information is carried via the optic tract The first synapse the optic tract makes is in the lateral geniculate nucleus of the thalamus which acts as a relay station to project visual information to the occipital lobe aka striate cortex primary visual cortex and area 17 and V1 Left visual field to left nasal retina and right temporal retina Right visual field to right nasal retina and left temporal retina Be able to describe the Flicker technique Rensink et al popularized the technique in which two images of scenes alternate repeatedly with a brief 80 millisecond blank screen after each image giving the display a flickering appearance With the blank screen in place surprisingly large changes could be made to the scene without the observer reliably noticing them Rensink et al 1997 also introduced the term change blindness Rensink et al 1997 emphasizes the need for attention to detect change Using the flicker technique the eyes must search each object in the scene in order to detect the change Changes to objects that are more important to the picture will be noticed more quickly than changes to objects less important to the scene you re more likely to scan the important objects first Know the optic pathway and where visual information crosses over Know the common type of color blindness Be able to explain why it is the most common hint slide 21 of change blindness Most common type of color blindness involve red green color vision Genes encoding red and green pigments are on the X chromosome It is the most common type because men s sex chromosome is XY Genes that encode for blue pigments are on chromosome 7 Color blindness is more common in men than women Know the types of cells in the layers of the retina circuitry and the sequence in which they are activated in response to light hint slide 20 and 21 of the peripheral color detection Retinal Pathway Messages photoreceptors at back of the eye bipolar cells retinal ganglion cells joined axons of the ganglion cells form the optic nerve that then travels to the brain Photoreceptor cells connect to Horizontal cells and Bipolar cells Bipolar cells connect to Amacrine cells and Ganglion cells Cross talk between cells in the same layer is achieved through the Horizontal cells and Amacrine cells What are convergence and accommodation How do they act as binocular cues As we shift focus from a far to a near point our eyes converge As we go from near to far the eyes diverge The human eye focuses via the process accommodation in which the lens gets fatter as we direct our gaze toward nearer objects Convergence is the ability of the two eyes to turn inward often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images typically on the fovea of each eye Convergence reduces the disparity of the feature to zero or nearly zero Divergence is the ability of the two eyes to turn outward often used in order to place the two images of the feature in the world on corresponding locations in the two retinal images typically on the fovea of each eye Divergence reduces the disparity of that feature to zero or nearly zero If we could monitor our state of accommodation and or the extent to which our eyes were converged we could use this information as a cue to the depth of the object we were trying to bring into focus the more we have to converge and the more the lens has to bulge in order to focus on the object the closer it is Be able to define the molecular and binocular cues used for depth perception Molecular cues for depth perception include Relative Size A distance cue making the larger of two objects appear closer to the observer Aerial Perspective refers to the clearness of distant details under different atmospheric conditions Interposition a distance cue in which one object s retinal image partially obscures another s so that the whole image appears closer to the observer Linear Perspective The decrease in size and separation of objects as they become more distant Motion Cues The apparent relative motion of several stationary objects against a background when the observer moves gives hints about their relative distance Size Constancy refers to the tendency of objects to be perceived as constant in size despite the fact that the size of objects on the retina vary greatly with distance Binocular cues
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