Attention
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Introduction
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definition of the construct
a bit of history
Spatial attention and early vision
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contrast
spatial resolution
some experimental methods
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Feature based attention
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Visual search
Attention

Introduction



a bit of history
some experimental methods
definition of the construct

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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
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endogenous : contrast gain
exogenous: response gain
endogenous attention potentiates effects of adaptation
Contrast sensitivity
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Exogenous: cost at unattended location
Exogenous overcomes adaptation and restores sensitivity
Attention signatures: Attention-plus-external noise paradigm
Pestillli & Carrasco, Vis.Res. 2005
Pestilli & Carrasco, Vis.Res. 2005
Pestilli & Carrasco, JoV 07
adaptation
Transient 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
Does attention intensify the sensory impression?
YES. Wundt, Mach, Helmholtz & Titchener
Yes, but it does not ever lead us astray
W. James
NO. Fechner
“what is the orientation of the higher
contrast stimulus?”
Methods
fixation point
500 ms
.
neutral cue
peripheral cue
.
cue
67 ms
.
ISI
53 ms
.
stimuli
40 ms
- non-predictive peripheral cue
- 2 x 2 AFC task: orientation contingent
on apparent contrast
response
1 s
.
Stimuli
Standard: 6 or 22 % contrast
Test: 2-80 % contrast
% perceived contrast test > Standard
Contrast appearance
100
n=16
p.s.e.
50
Test cue
Neutral cue
Standard cue
0
1
10
Contrast of Test stimulus
100
Contrast appearance
SOA - 500 ms
% perceived contrast: Test > Standard
SOA - 100 ms
100
50
Test cued
Neutral cue
Standard
n = 16 cued
0
1
10
100
1
n = 16
10
100
Contrast of test stimulus
Other controls: inverted instructions, postcue, cue polarity, appearance judgment w/o concurrent task
Attention alters contrast appearance
Test Cued
16%
Neutral
22%
Standard Cued
28%
Carrasco, Ling & Read
Nature Neurosci, 2004
Attention & appearance
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spatial frequency
Goebell & Carrasco, 2005
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apparent size
Anton-Erxleben & Treue, 2007
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motion coherence
Liu, Fuller & Carrasco, 2006
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flicker
Montagna & Carrasco, 2006
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speed
Turatto et al., 2007
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saturation, not hue
Fuller & Carrasco, 2006
Covert attention
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
enhanced contrast sensitivity at attended
location; diminished sensitivity at unattended
location
transient:
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performance – response gain
appearance
restores effects of adaptation (contrast gain)
sustained:

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performance – contrast gain
strengthens adaptation
Why use noise?
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
Campbell
& Robson
(1968)
Pelli & Farell 1999
Pelli & Farell 1999
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.
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.
Lu & Dosher, 1998, 200, 2002, 2004
External noise distinguishes mechanisms of attention
samples of 8 levels
of external noise
a Gabor embedded
in the external
noises
TVC functions, 3 d’
Signature of attention
mechanisms
Attention-plus-external noise paradigm
precue
valid : invalid
(5:1)
675
ms
150
ms
response cue
noise
signal
17
ms
4 possible
orientations
8 external
noise levels
method of constant
stimuli
External noise
exclusion
(but
Ling & Carrasco ’06)
External noise
exclusion
& stimulus
enhancement
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