Bi150 PS4_Answers_2011

Bi150 PS4_Answers_2011 - PS4 Answer Key Problem 1. Vision...

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PS4 Answer Key Problem 1. Vision (1.5 points) A. (0.6 point) Visual impairments a. Match each visual impairment listed below with a single lesion or mutation in the visual system that could be responsible for it. You should not use the same lesion/mutation twice. b. For each pair you have determined in part a. , explain briefly what is known about how the given lesion produces the specified visual impairment. (i) Complete loss of vision only in the temporal halves of both visual fields. (f) Complete saggital transection of the optic chiasm (cutting only those fibers that would normally cross there). - fibers crossing over in the optic chiasm receive inputs from the nasal half of the retina - nasal half of the retina receive stimuli from temporal visual field (ii) Complete loss of vision only in the superior quadrant of the visual field on the right side. The central area is unaffected. (c) Lesion of the lower bank of the calcarine sulcus in the left hemisphere. - lower bank carries information from the upper visual hemifield - left/right cross over - overrepresentation of the fovea (iii) Inability to perceive a pattern of bright and dark bars that have both low spatial frequency and high temporal frequency. (i) Mutation a selective loss of function of magnocellular ganglion cells in both retinae. - M cells are able to respond to stimuli with low spatial and high temporal resolution. - P cells were not lesioned as color contrast and high spatial frequency vision are still intact. (iv) Inability to see or dream in color. (b) Bilateral and complete lesion to cortical visual area V4. - V4 has been shown to be a very high level area involved in color perception in human lesion studies. (v) Difficulty to adapt to different light intensities quickly. (h) Mutation of cGMP-gated channels in the retina causing impermeability to Ca 2+ - Ca 2+ inhibits guanylyl cyclase - lowering the Ca 2+ concentration is believed to speed up the inactivation of the visual pigments, so that the effectiveness of a given light flash in activation cGMP phosphodiesterase is reduced. (vi) Inability to reach for visual objects normally.
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Bi150 PS4_Answers_2011 - PS4 Answer Key Problem 1. Vision...

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