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University of Toronto St. George
Kristie Dukewich

PSY280: Lecture 4 Notes 1. Calculate relative levels of activation of ON/OFF bipolar cells and centre- surround RGCs based on their relative inputs. 2. Describe how the spatial organization of the visual field is represented in the cortex (along with its distortions) a. Activity on the retina causes activity in the cortex. b. Vernier acuity and grating judgments both use just noticeable differences to estimate visual acuity in participants. 3. Describe evidence that shows cortical magnification contributes to visual acuity. a. It depends on how far the object it is from the eye. i. If a mouse is placed close and an elephant is placed far, they can occupy the same space on retina. b. To get an estimate of cortical magnification, researchers presented spots of light of varying visual angles and measured the size of the fMRI response. c. The higher a participant’s visual acuity, the greater their magnitude of cortical magnification. 4. Summarize the characteristics of the columnar organization in the striate cortex, including ocular dominance and hypercolumns. a. Neurons that are perpendicular to the surface of the cortex have receptive fields at approximately the same location on the retina. i. Same preference in space ii. Same preference of orientation of light b. When researchers cut across the orientation columns, they found orientation preference changed systematically. c. Ocular dominance is meandering, and orientation columns can have multiple configurations. d. There are more hypercolumns representing in fovea than in periphery. 1 5. Summarize the characteristics of the magnocellular and parvocellular pathways. a. Pathways from LGN to V1 stay segregated. i. This compartmentalization of brain allows specialization Visual function Magnocellular Parvocellular Retinotopic emphasis Peripheral Central Receptive field size Large Small Contrast sensitivity High Low Color sensitivity Low High Spatial resolution Low High Temporal resolution High Low - detects changes Motion sensitivity High Low Neural transmission Rapid Sluggish - ~fast draft - ~ portrait painting b. 6. Define and identify the extrastriate cortex. a. The extrastriate cortex borders V1 and is also important for visual processing: i. Broadmann’s Area 18 and 19 b. 2 7. Describe where information form the magnocellular and parvocellular pathways ends up beyond V1. a. Using electrophysiology, behavior and lesion studies, researchers determined these pathways extend beyond the striate cortex into the association areas. b. Association area is where connect the perception with meanings c. Magnocellular  V1  area MT (medial-temporal) i. MT: moving object d. Parvocellular  V1  V4 i. V4: stationary object form, color, shape ii. V4: literally below the MT 8. Recognize the difference between dorsal and ventral 9. Describe the separable functions of the dorsal and ventral pathways in the cortex. a. Dorsal: area MT  parietal lobe (“where” pathway) i. The dorsal pathway is responsible for determining where in space an object is. b. Ventral: area V4  temporal lobe (“what” pathway) i. The ventral pathway is responsible for determining the identity of an object. 3 c. The two pathways are highly interactive. Bidirectional crosstalk occurs. 10. Describe the reasoning behind ablation research. a. Ablation: if you don’t know what something does, remove it and see how the system now functions. b. The monkey with parietal lobe removed fails to remove the food well cover that is closest to the cylinder because there are no associations in space with the objects. c. The monkey with the temporal lobe removed fails to recall which item was previously presented because it can no longer discriminate the 2 objects. 11. Explain the landmark discrimination and object discrimination tasks, and how performance relates to lesions in the parietal or temporal lobes. a. Landmark discrimination: the goal
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