“Everyone knows what attention is… William James, 1890

What is visual attention?

... It is the taking possession by the mind, in clear and vivid form, of one out of what seem several

simultaneously possible objects”

Levels of analysis:1. Subjective (W. James)

2. Functional - cognitive (joke)

3. Neurological

1. Subjective level (phenomenology)

- if you don’t pay attention to it, you don’t see* it

* perceptual awareness

In normal subjects

Go mist

Change blindness

In patients with hemispatial neglect

move your eyes (& your attention)

you ‘see’ the change -- you are ‘perceptually aware’-- at the attended location

You are unaware at the unattended locations

Try to find the difference between these two pictures

Look for waldo

Steps to find Waldo1. Fixate attention

2. Decide: Is that him?

3. Disengage attention

4. Move attention

5. Fixate onto a new location

These are the Cognitive processes

Find the letter T

T

L

T

T

T

L

Anne Treisman

2. Cognitive Processes: Visual Search

2. Cognitive processes: How to study visual attention?

• Visual search (Treisman)– Overt movement (i.e., moves eyes)– It’s difficult to isolate specific steps (e.g. disengage)

• Covert orienting task (Posner) (aka spatial cueing task)– No eye movements – Isolates each step of the process

time

Covert orienting task

Mike Posner+

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+

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invalid20%

Valid80%

1 sec

0.5 sec

Mike Posner

250

270

290

310

330

350

Valido Invalido

RT (ms)

Covert orienting task

Arrow Onset

. Voluntary engagement of attention

Target onset at opposite location (invalid trial)

. Detect surprising event

. Disengage attention from initial site

. Move it to the opposite location

Covert orienting task

Voluntary Attentional System (dorsal).

<-Attention at the cued location

<-

15 sec delay

* Detect stimulus at unattended location

Automatic attentional system (ventral)Corbetta et al, nature neuroscience

Interaction between the two systems

Left IPS

Right IPS.

Right TPJ

balance

Modulated by expectations

Alerted by Unexpectedstimulus

Hemispatial NeglectAnatomy

TPJ, horizontal cut

Temporo-parietal junction (right)

Lesion can extend

toward frontal lobe

Interaction between the two systems post-stroke

SPI izq.

SPI der.

UTP der

IMBALANCE Alert by unexpected

stimulusGreatly reduced

LESION

Sintoms:??

Covert orienting task

Hemispatial neglect, clinical

- eye gaze: right side bias

- neglects stimulus in left visual field (bumps wall, misses food on that side of tray)

- low arousal (sleepy)

-Muscular weakness (hemiparesis): unrelated

Cancelation task

Line bisection

Star crossing

Clinical assessment

drawings

Bias in writing

- Extincion

Clinical evaluation (cont’d)

Q Does the disordered attentional mechanisms associated with visuospatial neglect alter patient’s representation of space ?

normal

neglect

Self portrait by Anton Raderscheidt, at different stages of recovery

3

21

4Drawings by Tom Greenshields

pre- and post-stroke

Before After

Visual search: Eye movements