Next Week

Memory:

Articles by Loftus and Sacks

(following week article by Vokey)

Features and Objects in Visual Processing

The Waterfall Illusion

QuickTime™ and aH.263 decompressor

are needed to see this picture.

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 (without attention)

– 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 colored shapes did you see?

Illusory Conjunctions

• Illusory conjunction - when perceived combination of attributes was not present

Illusory Conjunctions

• Illusory conjunction - when 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?

What’s another way to investigate pre-attentive feature processing?

Visual Search…why?

Visual Search• Parallel search - indicates pre-attentive processing of the feature that

distinguishes target from distractors• Serial search - indicates the target/distractor difference is processed only

with the help of attention

Search Slope

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Distractors

Response Time (ms)

Search Slope

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600

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1000

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0 10 20 30 40 50 60

Distractors

Response Time (ms)

Parallel Search Serial Search

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 along with other aspects of visual search?

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