Sensation _ Perception - lecture 8 - shape and pattern perception

Sensation _ Perception - lecture 8 - shape and pattern perception

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Lecture 8 Shape & Pattern perception
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Main questions in visual pattern perception: How do we extract pattern and shape from the wealth of edge information available and ultimately recognize something? How do we determine which edges go together? Visual Pattern Perception
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Approaches to visual pattern perception: Spatial Frequency Analysis Gestalt Psychology Computational Approach Template Matching Approach Visual Pattern Perception
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Analytical Orientation Holistic Orientation Emphasizes the importance of the components of a stimulus that combine to form our perceptual experience. Spatial Frequency Analysis. Emphasizes that objects are perceived as well- organized “wholes” instead of isolated parts. Gestalt Psychology. Visual Pattern Perception
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Builds on what we know about the bottom-up processes of the visual system. Brain breaks down the visual scene into a series of narrow light and dark stripes. “Active synthesizing process”. Spatial Frequency Analysis
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Fourier’s Theorem Basis of spatial frequency analysis approach… Spatial Frequency Analysis
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Fourier’s Theorem Proposes that we analyze any pattern of stimuli through a series of simpler sine wave patterns. Fourier Analysis Analyzes stimulus into its component sine waves. Breaks down the image. Fourier Synthesis Combines the different sine waves of a stimulus. Reconstructs the image. Spatial Frequency Analysis
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Frequency = the # of times light level goes from dark to light and back. Low Spatial Frequency The light intensity of gratings that possess very broad bars and spaces that rise and fall slowly. High Spatial Frequency The light intensity of gratings that possess narrow bars and spaces. Spatial Frequency Analysis
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Spatial Frequency Analysis
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Spatial Frequency Analysis So, does the brain find such an analysis useful? Is the visual system set up to conduct some sort of spatial frequency analysis for given patterns of light?
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We possess four sizes of spatial frequency filters. All our visual perception is done with these filters. Filters, are analogous to on-off (or off-on) receptors of the retina and visual system. Instead of working in an on/off fashion they are either black-white or white-black. Spatial Frequency Analysis
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Spatial Frequency Analysis Type of Filters Low Frequency. Medium Frequency. Medium-High Frequency. High Frequency. Filter = cells respond rapidly to a specific visual pattern, firing less rapidly to other patterns. Cells are filtering out all but a select set of stimuli.
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In essence, the neurons we’re abstractly talking about respond by firing more or less as a function of the extent to which the spatial frequencies in the image match the filter characteristics. Spatial Frequency Analysis
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This document was uploaded on 11/04/2011 for the course PSYCH 301 at Rutgers.

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Sensation _ Perception - lecture 8 - shape and pattern perception

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