Features and Object in Visual Processing

The Waterfall Illusion

QuickTime™ and aDV/DVCPRO - NTSC decompressor

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The Visual World is an Arrangement of Features

• Color

• Motion

• Form

• Depth

• Orientation

Pre-attentive vs. Attentive Processing

• Pre-attentive processing– Does the visual system register some basic

features automatically– if so, what features?– How would you know?

Pre-attentive vs. Attentive Processing

• Indicators of Pre-attentive processing

– 1. processing precedes orienting - if you shift your attention to something or someplace because of some processing you did on the information there, you must have done that processing without attending

Pre-attentive vs. Attentive Processing

• Indicators of Pre-attentive processing

– 2. processing done in parallel - if you can process features of several objects simultaneously, you must have done that processing without attention

Parts vs. Wholes

– We see wholes, but the visual system initially sees parts (i.e. features) of objects

Parts vs. Wholes

• For example:

Parts vs. Wholes

• Simple features form boundaries

Parts vs. Wholes

• Conjunctions don’t form boundaries

“Early parsing of the visual field is mediated by separate

properties, not by particular combinations of properties”

What does Treisman conclude from this observation?

• “Analysis of properties and parts precedes their synthesis”

• What is the “strong prediction” Treisman makes?

Illusory Conjunctions

• “errors of synthesis”

Illusory Conjunctions

• Identify the letter on the left of the screen and the digit on the right

Illusory Conjunctions

Q 4

Illusory Conjunctions

What shapes did you see?

Illusory Conjunctions

• Illusory conjunctions - perceived combination of attributes was not present

Illusory Conjunctions

• Illusory conjunctions - perceived combination of attributes was not present

• Supports notion that primitive features are processed independently and then bound together to form objects

What’s another way to investigate pre-attentive feature

processing?

Visual Search

• Search Slope: How long per item?

Visual Search

• Search Slope: How long per item?

Visual Search

• Search Slope: How long per item?

Visual Search

• Serial Search - linear increase in search time with number of distractors

Search Slope

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Distractors

Response Time (ms)

Visual Search

• Parallel search - search time is independent of distracter number

Search Slope

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Distractors

Response Time (ms)

Visual Search

• Search Slopes can be flat for targets defined by:– color– orientation– curvature– motion– depth

• What does this imply about these features ?

Visual Search

• But there are some caveats:– What is a search asymmetry?

Search Asymmetry

Search Asymmetry

Search Asymmetry

• But it’s the same discrimination…gaps vs. non-gaps !?

• What model does Treisman propose to explain search asymmetry?

Feature Integration Theory•Early visual system parses scene into features represented in “feature maps”

•“Attention Spotlight” can be moved across an overlay of these feature maps to bind features together

Feature Integration Theory

• What term does Treisman use to describe the bundle of features at a specific location?

Feature Integration Theory

• Object Files are mental (neural?) representations of the features associated with an object– whenever an object is selected by attention it’s

features are bound and an object file is opened– when the features of that object change, the

object file is updated

Feature Integration Theory

• How did Treisman et al. test whether the visual system uses object files?

Feature Integration Theory

• Priming: observers are faster to respond to something they’ve just seen

Feature Integration Theory

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Feature Integration Theory

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Feature Integration Theory

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Feature Integration Theory

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Feature Integration Theory

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Feature Integration Theory

What Letter?

Feature Integration Theory

• What was the result?

Feature Integration Theory

• What was the result?– Naming was faster if the prime occurred in the

same object, even though the object had moved

Feature Integration Theory

• What was the result?– Naming was faster if the prime occurred in the

same object, even though the object had moved

• Interpretation?

Feature Integration Theory

• What was the result?– Naming was faster if the prime occurred in the

same object, even though the object had moved

• Interpretation?– visual system establishes object files and

updates them as the location and features of the object change

Next Time:

• The Neurophysiology and Neuropsychology of attention