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PSYB51H3 Chapter Notes -Principles Of Grouping, Illusory Contours, Necker Cube

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Matthias Niemeier

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-Middle (midlevel) Vision: loosely defined stage of visual processing that
comes after basic features have been extracted from the image (early vision)
and before object recognition and scene understanding (high-level vision)
Middle Vision
- goal of MV: organize the elements of a visual scene into groups that we can then
recognize as objects
Finding Edges:
- trace the edge of the object with a finger must pass locations where there is no
diff b/w the luminance of the object and luminance of background these points
of the shape has no edge at all
- lack of edge doesn’t bother visual system hard to see the gaps
ovisual system knows they are accidents of lighting and fills in the contour
-Illusory Contours: contour that is perceived, een though nothing changes
from one side of the contour to the other in the image
Rules that make Contours:
-Structuralism: school of thought complex objects/perceptions could be
understood by analysis of the components
- Perceptions are the sum of atoms of sensationbits of colour, orientation, etc.
- Structualist’s view perception is built up of an array of atoms
-Gestalt: “form” in german; school of thought stresses that the perceptual
could be greater than the apparent sum of the parts
-Gestalt Grouping Rules: set of rules describing which elements in an image
will appear to group tgt
-Good continuation: Gestalt grouping rule stating that 2 elements will tend to
group tgt if they seem to lie on the same contour
Perceptual “Committees”
- “all else being equal”; everyone gets tgt and voices opinions about how the
stimulus ought ot be understood
oSometimes opinions collide results are unpredictable
oConsensus view one single interpretation of the visual scene
- Why does an edge sometime suddenly stop?

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ob/c something else gets in the way, hiding it from our view
onotches in the circle represent contours can be extended
inference of an illusory contour
Texture Segmentation and Grouping:
- because the edge-finding members of the “image-parsing committee” are of little
otexture segmentation: carving an image into regions of common
texture properties
closely related to Gestalt grouping principles
Similarity: G.G rule tendency of two features to group tgt
will increase as the similarity b/w them increases
Texture grouping can be based on similarity (color, size,
orientN, aspects of form)
oProximity: G.G rule tendency of two features to group tgt will
increase as the distance b/w them decreases
- Weaker grouping principles:
oParallelism: rule for figure-ground assignment stating that parallel
contours are likely to belong to the same figure
oSymmetry: rule for figure-ground assignment stating that
symmetrical regions are more likely to be seen as figure
-Principle of Common Region: G.G rule stating that two features will tend to
group tgt if they appear to be part of the same larger region
-Connectedness: G.G rule stating that two items will tend to group tgt if they
are connected
- the same principle that is used to help us find objects in the world can also be
exploited to hide them
Perceptual Committees Revisited:
- Low-level visual process deliver fairly str8fwd bits of information about a line
here and a colour there
oThe collection of info needs to be interpreted before we know what we are
- Middle vision behaves like a collection of specialists, each with a specific area of
expertise and indiv. Opinions about what the input might mean
oGoal: have a single answer emerge out of this diversity of opinions
Committee Rules: Honor Physics and Avoid Accidents:
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