visual_cog_08 - 1 Visual Cognition 2 Overview of Visual...

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1 1 Visual Cognition September 11, 2008 2 Overview of Visual Cognition • Visual system: mission critical • Multivariate inputs, unitary experience • Multiple types of vision means many types of units in a distributed visual network • Segregating vs. parsing • Visual experience reveals nature of underlying representations • Theory >> data 3 Who’s Coming to Dinner? Gestalt Psychology (interested in basic dimensions of perceptual organization) Cognitive Psychology (interested primarily in effects of cognitive operations on visual experience) Cognitive Neuropsychology (interested in effects of selective lesions of visual cortex on visual behavior) Electrophysiology (interested in single- and multiple-unit activity of cells in visual cortex) Cognitive science (interested in developing overall theories of visual experience and object recognition) 4 Sensation and Perception Sensation : Conscious outcome of sense organs and projection regions. (“I detect something”, not necessarily conscious, and not necessarily meaningful) Perception : means by which information acquired from the environment via the sense organs is transformed (organized) into conscious experiences of objects, events, sounds, tastes, etc. (“I know, recognize, appreciate what I am sensing, and it means something to me”) 5 Three Stages of Visual Processing • Reception: absorption of physical energy by receptors • Transduction: translation of physical energy into electrochemical activity of the nervous system • Coding: how information is encoded and represented; relationship between aspects of the physical stimulus and resultant nervous system activity (e.g., rate, temporal patterning of neuronal activity) Population coding Sparse coding 6 Basic Perceptual Phenomena You Already Know About Size and Shape Constancies : reflect mechanisms whereby perception of a distal object stays the same despite proximal changes in the perception – implies storage of a “structural representation” Depth Cues: monocular or binocular sources of information that convey information about relative distance of objects from viewer – involve cues about the structure, movement, and proximity of objects 7 8 9 Milner & Goodale: Perception-Action Model • Alternative to the Mishkin-Ungerleider model – Dorsal: “How do I interact with that object”? – Ventral: “What is that object”?
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