Pre-attentive Visual Processing: What does Attention do? What don’t we need it for?

Pre-attentive Visual Processing: What does Attention do? What

don’t we need it for?

Parts vs. Wholes

• Simple features form boundaries

Parts vs. Wholes

• Simple features form boundaries

Illusory Conjunctions

Q 4

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

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 10 20 30 40 50 60

Distractors

Response Time (ms)

Visual Search

• Parallel search - search time is independent of distracter number

Search Slope

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 10 20 30 40 50 60

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 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

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 its

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

+

Feature Integration Theory

+

G

N

Feature Integration Theory

+

Feature Integration Theory

+

Feature Integration Theory

+G

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 box, even though the object had moved

Feature Integration Theory

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

same box, even though the object had moved

• Interpretation?

Feature Integration Theory

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

same box, even though the object had moved

• Interpretation?– visual system establishes object files (e.g. a box

with a G in it) and updates them as the location and features of the object change

The Physiology of Attention

Physiology of Attention

• Neural systems involved in orienting

• Neural correlates of selection

Disorders of Orienting

• Lesions to parietal cortex can produce some strange behavioural consequences

ParietalLobe

Disorders of Orienting

• Lesions to parietal cortex can produce some strange behavioural consequences

– patients fail to notice events on the contralesional side

– Patients behave as if they are blind in the contralesional hemifield

Disorders of Orienting

• Lesions to parietal cortex can produce some strange behavioural consequences

– patients fail to notice events on the contralesional side

– Patients behave as if they are blind in the contralesional hemifield but they are not blind

• Called Hemispatial Neglect

Disorders of Orienting

• Patients will often “neglect” half of their visual field

Disorders of Orienting

• Hypothesis: Parietal cortex somehow involved in orienting attention into contralesional space