Transcript Document

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
What is attention
Everyone knows what attention is. It is the
taking possession of the mind, in clear and
vivid form, of one out of what seem several
simultaneous possible objects or trains of
thought. Focalization, concentration of
consciousness are of its essence. It implies
withdrawal from some things in order to
deal effectively with others, and is a
condition which has a real opposite in the
confused, dazed, scatterbrain state ….
– William James (1890)
Helmholtz on covert attention (1867)
“It is a curious fact, by the way, that the
observer may be gazing steadily at the two
pinholes and holding them in exact
coincidence, and yet at the same time he can
concentrate his attention on any part of the
dark field he likes, so that when the spark
comes, he will get an impression about
objects in that particular region only. In this
experiment the attention is entirely
independent of the position and
accommodation of the eyes, or indeed, of any
known variations in or on the organ of vision.
Thus it is possible, simply by a conscious and
voluntary effort, to focus the attention on
some definite spot in an absolutely dark and
featureless field. In the development of a
theory of the attention, this is one of the most
striking experiments that can be made.”
(Physiological Optics, Vol, 3, p. 455. Thoemmes Press Ed.)
Spotlight of attention
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Helmholtz observed
that we can enhance
perception, if we focus our
attention on a locati on in the
vi sual field.
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However, enhancing
perception in one part of the
vi sual field takes place at the
expense of other areas.
What is attention? Why?
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Two primary themes characterize attention:
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Perceptual gating (selection)
Conscious perception is always selective,
but selection is not always conscious
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Capacity limitation
Our limited ability to carry out various mental operations at the
same time
Competing hypothesis
• early selection - physical characteristics of messages are
used to select one message for further processing and all
others are lost (Broadbent, 1958)
higher processing stage
• attenuation - physical characteristics
are used to select one message for
full processing and other messages are given partial processing
(Treisman, 1964)
• late selection - all messages get through, sensory
butsignals
only one
response can be made (Deutsch & Deutsch, 1963)
Shadowing task
Somewhere Among hidden the in most the
spectacular Rocky Mountains cognitive near
abilities Central City is Colorado the an ability
old to miner select hid one a message box
from of another. Gold. We Although do several
this hundred by people focusing have our
looked attention for on it, certain they cues
have such not as found type it style.
When does the selection take place?
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Classic Theory I. Early Selection
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Filter theory proposed by Broadbent (1958)
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Because of our limited ability to carry out multiple
discriminations in parallel, only physical featural
analyses can be carried out in parallel.
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Counterevidence: findings of divided-attention
studies
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People are capable of fairly extensive parallel processing.
Ex. Letter search tasks
Broadbend‘s filter theory (1958)
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Early selection – selection is based on physical
properties of the stimulus (e.g., pitch, loudness)
Only one input channel can
higher processing stage
be processed at a time
Semantic interpretation
only after selection
Conscious control
It takes time to shift attention
sensory signals
When does the selection take place?
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Classic Theory II. Late Selection
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Proposed by Deutsch (1963)
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Perceptual analysis operates without capacity limitations
and without voluntary control.
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Counterevidence:
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Inattentional Blindness
Divergence of ERPs (Event-related potentials) very early after
presentation of a stimulus.
Late selection
Attended Channel: THE GIRL WAS dogs, six, beach ...
Unattended Channel: world, eight, WAITING FOR HER ...
Reported: THE GIRL WAS WAITING FOR HER ...
Sperling (1960) partial report
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An array of letters (three rows of four) was flashed briefly
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In whole report, the observer recalled as many letters as
possible, ~ 4.
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In partial report, a high, medium, or low tone, presented after the
offset of the array, indicated that the letters in only the top,
middle, or bottom row were to be reported, ~7
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Observers can selectively encode into memory a spatially
defined subset of the array—an act of spatial selective attention
Spatial attention: the selective processing of
information at a given location.
Posner, Nissen, & Ogden (1978)
Posner, Nissen, & Ogden (1978)
Attention plays a key role in perception
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1980s and early 90s:
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necessary for effortful processing
‘glue’ that binds simple features into an object
what attention does?
what processes does it affect?
last decade, effects of attention on perception:
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psychophysics
single-unit recording
neuroimaging
Limited resources
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The high-energy cost of neuronal activity involved in
cortical computation limits our ability to process
information:
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constant overall energy consumption available to the brain
neuronal metabolic cost depends on the spike rate
the cost of a single spike is high
average discharge rate of active neurons will determine how
many neurons can be active concurrently […1%! ]
The brain needs machinery for the system to allocate
energy according to task demand… selective
attention.
Lennie, Current Bio ‘03
Selective Attention
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… the amount of information coming down the optic nerve estimated to be in the range of 108 ~ 109 bits per second far exceeds what the brain is capable of fully processing
and assimilating into conscious experience …
C. Koch (2004)
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Selective Attention (processing input preferentially) is the
natural strategy for dealing with this bottleneck.
Selective Visual Attention
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Capacity Limitation
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As visual information traverses the successive cortical
areas of the ventral visual stream, the size of receptive
fields increase.
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Neurons in higher order areas with large receptive fields
have to deal with many visual stimuli that appear
simultaneously within their receptive fields.
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This is why the neurons which make up the visual system
are limited-capacity channels.
Visual attention
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facilitation and selection of information
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overt attention - head and eye movements
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covert attention - monitor the environment
inform eye movements
Spatial covert attention
sustained
transient
endogenous
controlled
goal-driven
300 ms...
cortical
feedback
exogenous
reflexive
stimulus-driven
80 - 120 ms
also subcortical
?
Campbell
& Robson
(1968)
Sensitivity (1 / Threshold)
Contrast sensitivity function
Spatial Frequency (cpd)
Attention enhances sensitivity
1 cpd
2 cpd
4 cpd
8 cpd
neutral
peripheral
Carrasco, Penpeci & Eckstein, Vis.Res. 2000
modified Naka-Rushton function; N = attentional parameter
Martinez-Trujillo & Treue ’02
Ling & Carrasco, Vis. Res. 2006
Ling & Carrasco, Vis. Res. 2006
Sustained attention & adaptation
Attention increases
signal intensity
Intensity increases and
lengthens adaptation
Does the enhanced signal due to sustained attention lead
to a stronger, longer-lasting adaptation effect?
Contrast thresholds
Fixation
1000 ms
neutral
sustained
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Cue + Adapter
50 ms -16 s
ISI
100 ms
Time
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Target
100 ms
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Response
1500 ms
Adapter: 50% contrast; counter-phase flicker (9 Hz)
2AFC orientation discrimination task (±3°)
response cue
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Adapt recovery
50 ms - 16 s
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Contrast threshold over time
Ling & Carrasco, Nature Neurosci 2006
Attentional effect:
neutral / attended threshold
Enhancement
Impairment
Ling & Carrasco, Nature Neurosci 2006
Attention benefit and cost
Ling & Carrasco, Nature Neurosci 2006
Sustained attention and adaptation
• Attention increases contrast sensitivity
• The attention state modulates adaptation:
enhanced signal strengthens adaptation,
impaired sensitivity over time;
diminished signal weakens adaptation,
improved sensitivity over time
Ling & Carrasco, Nature Neurosci 2006