NROS 418 Exam 1 Questions & Answers(RATED A+)

Why does the organization of the eye guarantee that we have a blind spot? Why can't we normally detect the blind spot? -ANSWER The blind spot occurs due to the lack of photoreceptors where the optic nerve and blood vessels exit the eye. Our brain fills the blind spot in by using information that surrounds the blind spot area using ipsilateral and contralateral visual input. What is different about the fovea and the rest of the retina? Why is visual acuity best when images fall on the fovea? -ANSWER The fovea is an area of the eye that has a high density of cone receptors and where light is focused on the retina. At this section, cones send input to 1-3 RGCs each, which supports the high visual acuity. The rest of the retina is rods and cones, with more rods as you move further away from the fovea. What are the main differences in the function of rods and cones? Why can't you see color in the dark? -ANSWER Rod cells are more sensitive than cone cells, and are involved in peripheral vision. They also support our night vision, as they only require one photon of light to activate. Cone cells are less sensitive and perceive color. They require many photons to activate. They perceive fine detail and rapid stimuli changes Cones are not sensitive at low light levels, as there is not enough "light" to perceive color Describe the connections that result in the on-center off-surround receptive field of a RGC. Do the same for an off-center on-surround RGC -ANSWER *On-Center Off-Surround* 1) Light hits the center 2) Cone hyper-polarized 3) Glutamate release decreased 4) On-center bipolar cell depolarized and transmitter release increased 5) Off-center bipolar cell hyper polarized and transmitter release decreased 6) Firing of on-center ganglion cell increased 7) Firing of off-center ganglion cell decreased 1) Light hits the surround 2) Cone depolarized 3) Glutamate released 4) On-center bipolar cell hyper polarized and transmitter release decreased 5) Off-center bipolar cell depolarized and transmitter release increased 6) Firing of on-center ganglion cell decreased 7) Firing of off-center ganglion cell increased What do we mean by the term "lateral inhibition?" What is the functional effect of such inhibition on the selectivity of a response to a stimulus. -ANSWER An excited neuron inhibits the response of its neighboring neuron. OFF center cells: surround receptor depolarized when dark, releasing glutamate onto horizontal cell, which released GABA onto OFF-center bipolar cell, hyperpolarizing it, decreasing neurotransmitter release Photoreceptors are depolarized at rest, thus releasing glutamate tonically. Why is this useful? -ANSWER It allows for a graded response to light (bright, dim , no), instead of just on or off. It allows for visual acuity and color vision, and detecting changes. What is a receptive field? Are the RGC receptive fields all the same size? What would the advantages of a large receptive field be? -ANSWER The place on a sensory surface that a stimulus must reach to activate that neuron Size governs spatial frequency of information Small Field: stimulated by high spatial frequencies and fine detail Large Field: Stimulated by low spatial frequencies and coarse detail Describe the organization of the LGN -ANSWER LGN is organized into layers 1-6. Layers 1 and 2 are magnocellular, and 3-6 are pravocellular. Pravocellular neurons have small receptive fields, high spacial frequency resolution Magnocellular neurons have large receptive fields, low spatial frequency, high temporal frequency resolution Why can we not call the LGN simply a relay station in the visual pathway? -ANSWER It not only passes information onto its target projects, but also processes and computes information, determining the position of every major element of "object space" What is the primary input layer for LGN axons entering V1? How is the retinotopic map achieved? Why is the fovea overrepresented in processing -ANSWER Layer IV-Calpha Layer IV-Cbeta (SEE CHART) Fovea receptive field is small but tightly packed. Receives lots of info, more cortical space dedicated to processing and representing that info While cells in layer IV of V1 are monocular, cells in other layers are binocular. Why would you expect retinotopy to be preserved in these cells? -ANSWER The superficial layers of V1 neurons receive monocular inputs from both of the 4C layers (one for each eye), all six LGN layers project to area V1. Magno and Parvo layers project separately into V1, but then get completely merged through the parallel pathways, preserving retinotopy How is the receptive field of a simple cell formed from the receptive fields of LGN cells? How does the receptive field of a simple cell differ from that of a complex cell? -ANSWER The LGN receptive fields stack and add to form the receptive fields of simple cells which then build up a complex cell. A complex cell is comprised of simple cells that: 1) The same preferred orientation 2) Overlapping RFs 3) Different arrangements of subregions What is an orientation column? How is orientation coded? -ANSWER OCs are located in V1 and appear as flat slabs that are parallel to each other, they are perpendicular to the surface of V1 and *discriminate for visual orientations and their motion* Cells in these columns are complex cells that respond to properly orientated lines in any location of the neuron's receptive field What is an ocular dominance column? -ANSWER Strips of neurons in V1 that respond to either the psi- or contralateral eye. They span multiple cortical layers and are laid out in a striped pattern, lying