Chapter 6 summary - Cognitive Neuroscience: The Biology of the Mind PDF

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Summary of Chapter 6, broken down, easy to understand, and all in one place. Includes information from the powerpoint, book, and emphasized information from lectures....

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Ventral vs. Dorsal visual pathway 

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What vs. Where pathways o The ventral pathway is known as the “what” pathway. It handles object perception and recognition and terminates in the temporal cortex. o The dorsal pathway is known as the “where” pathway. It handles spatial perception and terminates in the posterior parietal. Evidence for this dissociation o Evidence found in the electrophysiological properties of neurons o Temporal and Parietal neurons respond differently to stimuli o Shown in various case studies involving lesions for animals and humans, as well as PET scans of humans. Temporal vs. Parietal lobes o Temporal lobe neurons  Selective  Receptive fields concentrated mainly on fovea (center of retina)  Only a minority of cells will fire to any stimuli (41%)  Most cells are selective to particular stimuli (59%) o Parietal lobe neurons  Nonselective  Respond to any stimulus (light, line, photo, etc.)  40% of receptive fields near fovea, but many around periphery.

Visual Processing Deficits 

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Apperceptive vs. Associative Agnosia o Apperceptive Agnosia  Problems extracting visual information from the world (perceptual deficit)  Cannot copy images, perception is impaired  Right Occipitotemporal pathway often damaged o Associative Agnosia  Problems using perceptual representations to access semantic information  Can copy images, perception is intact  Lesion to Left Occipitotemporal region Integrative Agnosia o Unable to process the world “at a glance” o Can recognize visual elements, but not able to integrate them into a whole Auditory Agnosia o The inability to recognize or differentiate between sounds.

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o Associated with brain damage to association area of the auditory cortex in the temporal lobe. Optic Ataxia o Can recognize objects – (e.g. orientation of slot) o Cannot use visual information to guide actions (e.g. grasping, pointing, walking) o When reaching for an object they cannot move directly towards it. o Looks like a visual impairment, although visual acuity is fine. o Loss of spatial understanding is manifested in inappropriate or misdirected limb movements and incorrect eye movements (saccades). Category Specific Agnosia (living vs. nonliving) o Discrepancies in ability to identify inanimate objects compared to the ability to recognize animate objects o Gross deficits in general memory

Theories of Object Recognition 

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Object Constancy o Visual input is highly variable - angle, illumination, context, etc. Yet, we can still recognize objects View-dependent vs. view-invariant theories o View-dependent  Extract basic features, recognition depends on point of view  Match features to “cornucopia of specific mental representations”  Huge demand on visual memory o View-invariant  Sensory inputs define basic properties, and main features are encoded and recognized across varied viewpoints.  Holistic level of recognition and analysis

Shape Encoding 

Ensemble hypothesis vs. hierarchical hypothesis o Ensemble hypothesis  Objects are represented by complex feature detectors  The collective activation of a population of detectors leads to perception of an object  Similar items can activate overlapping populations of neurons.  Novel objects are recognized by activating some matching features of familiar objects  Cells in temporal lobe have relative selectivity, not absolute

e.g., Cells responding to hands respond to all hands, not just Joe’s hand o Hierarchical hypothesis  Initial coding of basic properties (“features”)  Outputs feed into higher level representations (“leg”)  Eventually represent complex items (“table”)  Object coding by Gnostic Units: neurons that recognize a complex object encountered in the past.  Cells in Inferior Temporal Gyrus and Superior Temporal Sulcus identified as selective to faces, aka grandmother cells 

Face Processing 

Roles o Fusiform Face Area  Fusiform gyrus consistently activated across many studies, generally referred to as “Fusiform Face Area” (FFA)  However, FFA is not the only region that shows response to faces (e.g., primate studies STS)  Hypothesis: different brain regions are important for different aspects of face processing  FFA is critical for invariant facial properties  Superior Temporal Sulcus may process more dynamic features (Haxby et al., 2000). o Parahippocampal Place Area  Identification of area within the parahippocampal gyrus that responds to 

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pictures of scenes or landscapes (i.e., “places”) Activation in PPA is observed when people are asked to make judgments about spatial properties, such as “Is this scene indoors or outdoors?” or “Is there water in this picture?

Dissociation of face and object recognition o Patients known to not be able to identify individual “features” of an image of a bowl of fruit that is similar to that of a face. Prosopagnosia o Inability to recognize familiar faces (Bodamer, 1947) o Prosopagnosics have visual perception deficits that are disproportionate for faces o Brain damage and congenital causes have been reported  Bilateral occipital damage can cause prosopagnosia, but genetic variations have also been linked to impaired face perception...