attention

sensory input

respo

nse

perception

Attention, perception, and performance

• Attention: what is it good for?• Fronto-parietal lesions and hemifield neglect.• Behavioral measures of attention.• Neural correlates of attention.• Computational model of attention• Linking physiology and behavior.

Outline

Attention: what is it good for?

Limited resource- Energy metabolism in the brain can support only ~0.1 spikes/sec/neuron on average.- Perform only one action (eye movement, arm movement, etc.) at a time.

Makes downstream processing easier:- Ignore irrelevant neuronal signals.- Boost reliability of the relevant signals.

Working memory/awareness

Fronto-parietal lobe lesions

Symptoms: neglect extinction denial spatial orientation deficit

Cortical areas damaged

Neglect

Model Patient copy

Line bisection(patient: Frederico Fellini)

Patient PP

I knew the word “neglect” was a sort of medical term for whatever was wrong but the word bothered me because you only neglect something that is actually there, don’t you? If it’s not there, how can you neglect it?

I think concentrating is a better word than neglect. It’s definitively concentration. If I’m walking anywhere and there’s something in my way, if I’m concentrating on what I’m doing, I will see it and avoid it. The slightest distraction and I won’t see it.

Neglect

Extinction

Change blindness

Change blindness

• Eye movements• Reaction time vs performance accuracy• Performance vs criterion• Transient vs sustained• Visual search & feature integration theory• Search revisited with signal detection theory

Behavioral measures of attention

Eye movements

Reliability of eye movements

Covert attention

Measuring behavioral improvements with attention:- Reaction time vs accuracy.- Performance improvement vs criterion shift.- Exogenous (transient) vs endogenous (sustained) attention.

Visual search

Feature integration theory

Conjunction search: find vertical rectangle

Set size effect

Rea

ctio

n tim

e (m

s)

Display size

conjunction

single feature

Cueing protocol

+

++

+ +

+

+

++

+

+ +

+

++

+

Relevantset size 1

Relevantset size 8

Relevant set size

Cont

rast

incr

emen

t th

resh

old

Target appears at one of the cued locations on half the trials

Signal detection theory

yes no

Decision integration theory

Decision rule: subject monitors all stimulus locations, target present if any response exceeds criterion.

Set size effect: with a large set size, lots of opportunities for false alarm.

Attention is controlled in posterior parietal and prefrontal cortex

- Parietal (LIP) responses depend on behavioral relevance of the stimulus.

- Possible human homolog of monkey LIP.

Neural correlates of attention

Trained to fixate. Small response from parietal lobe neuron when light comes on in periphery.

Trained to fixate until peripheral light comes on, then must move eyes to look at the light. Identical retinal stimulation. Much bigger response (3x).

Trained to move arm instead of eyes. Same result (bigger response), i.e., not an eye movement control signal. Rather more like the neural correlate of attention/salience.

Neural correlates of attention: LIP

Human visual cortical areas

V1

V2

V3

V3A/BV7

IPS1IPS2

V4

LO1LO2

MT

V2V3

V3A/B

V7IPS1

IPS2

V4

MTLO2LO1

IPS1 and IPS2

0

0.5

1

0

0.5

1

0

0.5

1

0

0.5

1

0 10 20 30Time (s)

0

0.5

1

fMR

I res

pons

e (%

sig

nal c

hang

e)

3s

4.5s

6s

7.5s

9s

12s

15s

10.5s

13.5s

0 10 20 30Time (s)

data: mean ± se

model: mean ± sd

delay period

control

Sustained delay-period activity

Neural correlate of sustained attention (or intention)

peripheral target

delay

fixation dimssaccade

returnsaccadecorrective

saccade

A

B

DC

!14 0 +14!11

0

+11

Vert

ical

pos

ition

(d

egre

es)

Num

ber o

f tria

ls

total # of trials per session: 96

cont

rol t

rials

Figure 1

FPT

E

target cue ‘go’ correction

time1.5-15s

delay1.5s 1.5s 10.5-15s

return

0

5

10

15

20

Horizontal position (degrees) Delay period (s)3 6 9 12 15

Delayed saccade task

Attentional modulation in visual cortex

optic nerve

LGN

primary visual cortex

Retinogeniculate pathway

opticchiasm

Attention affects responses in visual cortex

- Boosts baseline firing rates in visual cortex.

- Boosts gain of responses in visual cortex.

- Selects one of multiple stimuli.

Attention increases baseline firing rates

cue start of trial

stimulus is presented

Attention increases gain of neural responses

V4

One stimulus within receptive field and the other contralateral.

Selection

Contrast gain & response gain

Reynolds, Pasternak, & Desimone, Neuron, 2000

Williford & Maunsell, J Neurophysiol, 2006

Log Contrast

C

0

1

AttentionalModulation(%)

NormalizedModelResponse

Log Contrast

F

0

1

NormalizedModelResponse

Predominantly Response Gain

AttentionalModulation(%)

B

Log Contrast0

1

Predominantly Response Gain

NormalizedModelResponse

AttentionalModulation(%)

Log Contrast

E

Mixed Attention Effect

0

1

NormalizedModelResponse

AttentionalModulation(%)

Log Contrast

D

Mixed Attention Effect

0

1

NormalizedModelResponse

AttentionalModulation(%)

Predominantly Contrast Gain

Log Contrast

A

0

1

NormalizedModelResponse

AttentionalModulation(%)

Mixed Attention Effect

AttentionField

Stimulus Ignored AttendedAttentionModulation

ReceptiveField

Figure 4

0

100

0

100

0

100

0

100

0

100

0

100

Attended Preferred

Attended Null

Attention Field

Attentionalmodulation(%)

100%

0%

50%

80%

20%

66

0

33

C

FiringRate(Hz)

Attentionalmodulation(%)40

35

30

25

20

15

100%

0%

50%

B

FiringRate(Hz)

A

AttentionField

Stimulus Ignored Attended% AttentionalModulation

ReceptiveField

Figure 4

Log Contrast Log Contrast

Normalization model of attention

Orientationpref

Orientationpref

Attention FieldRF center

RF center

pool overspace andorientation

Orientationpref

RF center

Stimulus

Orientationpref

Stimulus Drive

RF center

Suppressive Drive

XX

Figure 1

Population Response

Receptive fields Normalization

firing rate response÷

Attention

distractors

target

Stimulus

X

XX

X

X

+

Normalization model

Orientationpref

Orientationpref

Attention FieldRF center

RF center

pool overspace andorientation

Orientationpref

RF center

Stimulus

Orientationpref

Stimulus Drive

RF center

Suppressive Drive

XX

Figure 1

Population Response

R(x,θ) = E(x,θ) A(x,θ)S(x,θ) +σ

⎢

⎣⎢

⎥

⎦⎥

E(x,θ) = e(x,θ)∗ I(x, y) = I(ξ,η)e(∫∫ x − ξ, y −η)dξ dη

S(x,θ) = s(x,θ)∗[E(x,θ) A(x,θ)]

Normalization model

Normalization model

Σ( )normalizedresponse

(unnormalized response)2

unnormalized 2responses

+ σ2

=

Surround suppression

CRF

SurroundSurround ck

sk

CRF

Surround

0 < β < 1 surround suppression

Contrast gain vs response gain

Contrast gain change Response gain change

Small stimulus, large attention field

attentional gain affects stimulus drive and suppressive drive equally

γ > 1

r = α cc +σ

r = α γ cγ c +σ

= αc

c +σ / γ

Large stimulus, small attention field

attentional gainγ > 1

0 < β < 1 surround suppression

r = α cc + βc +σ

r = α γ cγ c + βc +σ

For c >> σ r = α 11+ β

For c >> σ r = α γγ + β

Attention protocol

Time(ms)

Neutral InvalidValid

ITI(1050-1550)

Pre-cue(60)

Stimuli(30)

Response cue(100)

ISI (40)

Interval(200)

1/3 each

Manipulating stimulus & attention field size

Large stimulusno spatial uncertainty

Small stimuluswith spatial uncertainty

Psychometric functions

> 9000 trials/observer4 observers

Large stimulussmall attention field

Small stimuluslarge attention field

Contrast (%)

Perf

orm

ance

(d’)

C50 p < .05

d’max p < .05

C50 n.s.

d’max n.s.ValidNeutralInvalid

10 100

2

3

1

0

10 100

2

3

1

0

Orientationpref

Orientationpref

Attention FieldRF center

RF center

pool overspace andorientation

Orientationpref

RF center

Stimulus

Orientationpref

Stimulus Drive

RF center

Suppressive Drive

XX

Figure 1

Population Response

Attention field sizeAttention field: spatial spread and featural extent of attention gain factors.

Small targets with spatial uncertaintyvs.

No uncertainty (always middle of 5 locations)

Measuring attention field size

De-emphasize stimulus-evoked responses:• Brief (50 ms) stimulus

presentations.• Small stimuli (<1° radius).• Low (10%) contrast.

Distance from the lower vertical meridan (arc deg of visual angle)fM

RI r

espo

nse

ampl

itude

: cue

d-un

cued

(%

cha

nge

imag

e in

tens

ity)

0 2 4 6 8 10 12 14 16 18

0

0.2

0.4

0.6

-0.2

fMRI response amplitudeAttention field centerAttention field size

Attention field size no uncertainty(arc deg visual angle)

Atte

ntio

n fie

ld s

ize

with

unc

erta

inty

(arc

deg

vis

ual a

ngle

)

0 2 4 6 8

2

4

6

8

Left hemisphereRight hemisphere

(deg polar angle)0 20 40 60 80 100 120 140 160 180

Sample hemisphere All hemispheres

Attention field size

Microstimulation in FEF improves performance

Microstimulation in FEF boosts gain of V4 responses