PSYC 256 Lecture Notes - Lecture 6: David H. Hubel, Railways Act 1921, Word Superiority Effect

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13 Jun 2018
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OBJECT RECOGNITION
Top-down vs Bottom-up Processing
Bottom-up
o We use the physical properties of the stimulus to determine the nature of the
object
Top-down
o We use conceptual information to interpret the physical properties of the
stimulus which in turn influences our ability to identify the object
o E.g., see a stick or brown belt in the woods and infer it is a snake
Object Perception is NOT
Template-matching
o Compare stimulus to large number of stored patterns, or templates, to
determine identity
o Problems:
Would need infinite number of templates
Requires multiple templates to represent the same object
No mechanism for creation of new templates
Object Perception includes Feature analysis
Stimuli made of combined elementary features (e.g., lines, shapes, angles)
Analyze component features to determine stimulus identity
Evidence from physiological studies: Hubel and Weisel (1960s)
o Cells are tuned to lines of a particular orientation
o Cat’s electrodes fired when the faint line went across the screen, not at the
colored dots
o Vertical lines
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o
Beyond Basic Features
Biederman’s geons
o Geometric components of objects
o
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Recognition by Components
Break an image (object) down into its constituent components
o edges/concave surfaces
o Geons and their interconnections
Then compare with stored representations (not templates)
Evidence: recognizing degraded objects
o
Gestalt
Basic Tenet
o The whole is more than a sum of its parts.
Law of Prägnanz
o Individuals organize their experience in as simple, concise, symmetrical, and
complete manner as possible
We impose order
Figure and Ground
Tendency to divide any visual scene into:
o Figure → object of attention
o Ground → background
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