PSYC 256 Lecture Notes - Lecture 6: David H. Hubel, Railways Act 1921, Word Superiority Effect
13 Jun 2018
School
Department
Course
Professor
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
find more resources at oneclass.com
find more resources at oneclass.com
o
Beyond Basic Features
• Biederman’s geons
o Geometric components of objects
o
find more resources at oneclass.com
find more resources at oneclass.com
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
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Beyond basic features: biederman"s geons, geometric components of objects. Recognition by components: break an image (object) down into its constituent components, edges/concave surfaces, geons and their interconnections, then compare with stored representations (not templates, evidence: recognizing degraded objects. Gestalt: basic tenet (cid:498)the whole is more than a sum of its parts. (cid:499, law of pr gnanz. 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, figure object of attention, ground background. Influenced by top-down processing: bottom-up, determined by certain stimulus characteristics, circumscription what surrounds is the ground, top-down. It is also determined by the subject: reversible figures. If in forest, would perceive belt as a snake. Gestalt principles: problem: circular logic, why do you see complete circle, because circle is the simplest form, why is it simple, because we easily process it.
