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PSYD50 notes 4.doc

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Jonathan Cant

Article#1: Acortical representation of the local visual environment Present that a particular area within human parahippocampal cortex is involved in perceiving the local visual environment. This area is the parahippocampal place area (PPA) PPAresponds selectively and automatically to passively viewed scenes Prediction is that the PPArepresents places by encoding the geometry of the local environment Previous studies: buildings without background can have a large response in cortical regions near the collateral sulcus (buildings are large stable structures that define the geometry of local space, or subjects were familiar with spatial context of landmarks).Also patients with damage to parahippocampal cortex experience great difficulty finding their way around novel environments Methods: 10 right handed students ( 1 omitted) performed experiment 1 and 2. They were scanned with fMRI while viewing 5.5 min videotapes. Contained scrambled and intact versions of black and white photographs of faces, common objects, houses and scenes Each subject was run on 2-3 scans for both the passive and 1 back tasks for each experiment - back task: press a button whenever they saw two identical pictures in a row. Each scan lasted 5 min and 36s , each photograph presented for 300 ms, blank interval of 500ms In all subjects, greater activation was found during presentation of intact scenes than during presentation of intact faces and objects in the PPA PPAresponds selectively to visually presented scenes even when the response to some of the low level features Questions: (1) If the PPAis involved in representing the shape of the local environment then it should be strongly activated by scenes even when they depict only bare spatial layouts without discrete objects. (2)If the PPAis involved in an analysis of the identities, meanings, or relative locations of the objects in the scenes then it should be more active for arrays containing multiple objects than for bare spatial layouts Experiment 2: 6 participants viewed photographs of (1)unfamiliar indoor scenes of rooms with furniture, plants etc…, (2)same rooms photographed from the same angle after all of the objects had been removed (3) arrays (4) faces (5) single objects (6) familiar outdoor scenes (7) outdoor scenes (8) familiar landmarks PPAresponded more strongly to scenes depicting bare spatial layout than it did to faces, objects or multiple object arrays. PPAresponse to empty rooms was as strong as the response to the same rooms furnished Presence of multiple objects is neither sufficient nor necessary for activation of the PPA Scenes depicting the shape of the local environment activate PPAeven if they are bare and uninteresting Also investigated whether response in the PPAwould be reduced if the surfaces in the stimulus did not define a coherent space. 5 subjects- viewed images of a new set of empty rooms fractured into component surfaces ( fractured rooms or fractured+rearranged rooms) PPAresponded more strongly to intact and fractured rooms than to fractured + rearranged rooms: difference in response reflect fact that the fractured rooms defined coherent space. Evidence that PPAperforms analysis of the shape of the local environment that is critical to our ability to determine where we are Article#2: Viewpoint-Specific Scene Representations in Human Parahippocampal Cortex PPAresponds more strongly to scenes than to faces, objects or other visual stimuli Study to test whether the PPArepresents scenes in a viewpoint-specific or viewpoint- invariant manner Past research, region in posterior parahippocampal cortex responds significantly more strongly to environmental scenes th
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