Introduction definition of the construct a bit of history

Spatial attention and early vision contrast spatial resolution some experimental methods

Feature based attention

Visual search

AttentionAttention

Introduction a bit of history some experimental methods definition of the construct

spatial vs. feature-based vs. object-based spatial: overt vs. covert attention covert: endogenous (sustained) vs. exogenous (transient)

Spatial attention and early vision contrast sensitivity

endogenous : contrast gain exogenous: response gain endogenous attention potentiates effects of adaptation

Contrast sensitivity Exogenous: cost at unattended location Exogenous overcomes adaptation and restores sensitivity Attention signatures: Attention-plus-external noise paradigm

AttentionAttention

Pestillli & Carrasco, Vis.Res. 2005

Pestilli & Carrasco, Vis.Res. 2005

Pestilli & Carrasco, JoV 07

adaptationadaptation

Transient attention and adaptationTransient attention and adaptation

Attention: response gain ~ Ling & Carrasco, Vis. Res. 06

Adaptation: contrast gain

Benefit and cost are similar regardless of adaptation state

Attention overcomes adaptation and restores contrast sensitivity

Pestilli & Carrasco, JoV 07

YES. Wundt, Mach, Helmholtz & Titchener

W. James

Does attention intensify the sensory impression?Does attention intensify the sensory impression?

NO. FechnerYes, but it does not ever lead us astray

- non-predictive peripheral cue

- 2 x 2 AFC task: orientation contingent

on apparent contrast

.

.

.

.

.

fixation point 500 ms

cue 67 ms

ISI 53 ms

stimuli 40 ms

response 1 s

neutral cue peripheral cue

MethodsMethods “what is the orientation of the higher contrast stimulus?”

StimuliStimuli

Standard: 6 or 22 % contrast

Test: 2-80 % contrast

Contrast appearance

1 100

100

50

100

n=16

Contrast of Test stimulus

% p

erce

ived

con

tras

t tes

t > S

tand

ard

Test cueNeutral cueStandard cue

p.s.e.

1 10

SOA - 500 ms

100

n = 16

1 100

50

100

n = 16

100

% p

erce

ived

con

tras

t: T

est

> S

tand

ard

Test cuedNeutral cueStandard cued

Contrast appearance

SOA - 100 ms

Contrast of test stimulus

Other controls: inverted instructions, postcue, cue polarity, appearance judgment w/o concurrent task

Attention alters contrast appearance

Test Cued Neutral Standard Cued

16% 22% 28%

Carrasco, Ling & ReadNature Neurosci, 2004

Attention & appearance

spatial frequencyGoebell & Carrasco, 2005

apparent size Anton-Erxleben & Treue, 2007

motion coherenceLiu, Fuller & Carrasco, 2006

flickerMontagna & Carrasco, 2006

speed Turatto et al., 2007

saturation, not hueFuller & Carrasco, 2006

Covert attention

enhanced contrast sensitivity at attended location; diminished sensitivity at unattended location

transient:transient: performance – response gain appearance restores effects of adaptation (contrast gain)

sustained:sustained: performance – contrast gain strengthens adaptation

Noise limits all forms of communication, including vision.

Visual sensitivity is a product of two factors that are each invariant with respect to many properties of the stimulus and task. By estimating efficiency and equivalent noise, one can isolate visual processes more easily than by using sensitivity measures alone.

Measure the human observer's threshold with and without a noise background added to the display, to disentangle the observer's ability from the observer's intrinsic noise.

Calculate ideal performance of the task at hand, as a benchmark for human performance. This strips away the intrinsic difficulty of the task to reveal a pure measure of human ability.

Denis Pelli

Why use noise?Why use noise?

Campbell & Robson (1968)

Pelli & Farell 1999

Pelli & Farell 1999

10

-6

10

-5

10

-4

10

-3

10

-2

10

-9

10

-8

10

-7

10

-6

10

-5

b

Noise power density N (deg

2

)

Signal energy

E

(deg

2

)

Perceptual processes are limited by various sources of noise - intrinsic stimulus variability, receptor sampling errors, randomness of neural responses, loss of information during neural transmission.

Perceptual template model (PTM)

Theoretical and empirical framework to assess the mechanisms of attention by systematically manipulating the amount and/or characteristics of the external noise added to the stimuli and measuring modulation of perceptual discriminability.

Lu & Dosher, 1998, 200, 2002, 2004

samples of 8 levels of external noise

a Gabor embedded in the external noises

TVC functions, 3 d’

External noise distinguishes mechanisms of attention

Signature of attention mechanisms

Attention-plus-external noise paradigm

8 external noise levels

4 possible orientations

precuevalid : invalid

(5:1)

signal

noise

response cue

150 ms675

ms

17 ms

method of constant stimuli

External noise exclusion

External noise exclusion& stimulus

enhancement

(but Ling & Carrasco ’06)

Signal enhancement

- suprathreshold target stimulus - no distracters- no local or global masks- no location uncertainty- response cue

e.g.,Cameron, Tai & Carrasco 2002; Ling & Carrasco, 2006

PTM

Dosher & Lu. 2000