learning objectives topics - wofford...

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Chapter 3

Perception: Pattern or object recognition

Learning Objectives Topics �  How are Sensation and Perception different? �  Bottom-up vs. Top-Down processing �  Bottom up Processing

�  Feature Detectors �  Experience Dependent Plasticity � Recognition by Components

�  Top Down Processing �  Influence of prior knowledge �  Perceptual Organization

�  Gestalt “Laws”

� Motion

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What is the difference between sensation and perception?

How does perception happen?

�  How do we interpret lines and patterns as objects?

�  How could we program a computer

to do this?

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How does perception happen? �  Start simple: How do we recognize these letters as A’s?

Template approach �  Stimulus is compared to stored pattern �  Examples?

�  Bar code, bank check, scantron, etc.

�  Problems: �  There are an infinite number of TEMPLATES to remember �  Have to learn a template first �  Any change in stimuli will not be recognized

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Some cannot do what we do effortlessly

�  Case studies: no damage to their visual system (sensation) – the problem is with perception!

�  Visual agnosia � Will talk about in knowledge chapter � Cannot recognize visually presented objects �  http://www.youtube.com/watch?

v=rwQpaHQ0hYw&feature=PlayList&p=D7F0F8EA3571F295&playnext=1&playnext_from=PL&index=14

Some cannot do what we do effortlessly

�  Case studies: no damage to their visual system (sensation) – the problem is with perception!

�  Prosopagnosia �  Damage to the fusiform gyrus

http://www.youtube.com/watch?v=VKa-PuJCrO4&feature=PlayList&p=D7F0F8EA3571F295&index=15&playnext=2&playnext_from=PL

�  As you watch…. �  At the most basic level, what can’t people with prosopagnosia do? �  What does this tell us about how perception works?

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What we can learn from case studies?

�  Feature detection �  separate from simple visual encoding � without can not recognize just by overall pattern (Gestalt)

�  Then we need to joining the pattern with a meaning and a name – knowledge stored in memory





� Motion

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The Complexity of Perception

� Bottom-up processing � Perception may start with the senses � Incoming raw data � Energy registering on receptors

� Top-down processing � Perception may start with the brain � Person’s knowledge, experience,

expectations

Here is a picture of an young woman:

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Bottom Up vs. Top Down Processing

Bottom up = stimulus driven

Dr. Steinmetz said it’s a young woman!

Top Down = thought driven





� Motion

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Bottom-up: What is the path to the visual cortex?

�  Specialized receptors in visual cortex �  Simple cells: feature detectors

�  e.g. Orientation specific

�  Complex cells �  Combination of 2 simple features �  e.g. orientation and movement

�  Perception due to pattern of neural firing (neural code)

Bottom-up processing

Stimulus

Cell’s responses

http://www.youtube.com/watch?v=IOHayh06LJ4

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Can we use features to determine letters?

�  How many feature units in this letter:

A

McClelland & Rummelhart (1981) Interactive Activation Model

A model for recognizing letters by analyzing their features.

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Our feature detectors can change based on the environment!

�  Blakemore & Cooper, 1970: What happened with the kitten that grew up in the striped room?





� Motion

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Experience-Dependent Plasticity �  Respond to things that occur most often in environment

�  e.g orientation: horizontal and vertical lines vs. oblique

�  Gauthier et al. (1999): “Greebles” study � Measure FFA (fusiform area) �  IV: experience with Greebles

Experience Dependent Plasticity

FFA = not just for faces! For recognizing complex objects.

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� Motion

Recognition by components �  Biederman’s RBC (recognition by component) theory �  36 geons (3D) �  Basic building blocks �  How do we recognize geons?

�  Intersections

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Recognition by components

�  Recognition with missing information possible

�  BUT if show object really quickly - People make more errors if a component is deleted

Geons: Identify objects Principle of componential recovery

�  Resistance to visual “noise”

�  ‘View invariant’ properties

� Discriminability

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Geons �  Why is it important to identify objects with geons missing in

everyday life?

Biederman’s Geons �  Intersections are important to recognition

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Limitations of RBC �  Over-reliance on stimulus-driven processes?

�  Ignores how context influences object recognition

�  Neuropsychological evidence? �  some brain damaged individuals understand parts but not whole!

Pattern or object recognition �  Bottom-up processing

�  Information from sensory receptors �  Processing driven by stimulus �  Data-driven

�  Top-down processing �  Information from knowledge and expectations �  Processing driven by higher level knowledge �  Conceptually-driven

�  Problems with pure bottom-up theories: �  How does brain pull all the feature information together? �  How do theories deal with complex objects?

learning objectives topics - wofford...

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