definition of the construct

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Attention

• 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

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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.)
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What is attention? Why?

• Two primary themes characterize attention
• Perceptual gating (selection)
• Conscious perception is always selective,
• but selection is not always conscious
• Capacity limitation
• Our limited ability to carry out various mental
  operations at the same time

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Competing hypothesis
early selection - physical characteristics of
messages are used to select one message for
further processing and all others are lost
(Broadbent, 1958) attenuation - physical
characteristics are used to select one message
for full processing and other mes-sages are
given partial processing (Treisman, 1964)
late selection - all messages get through, but
only one response can be made (Deutsch Deutsch,
1963)
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Shadowing task
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When does the selection take place?

• Classic Theory I. Early Selection
• Filter theory proposed by Broadbent (1958)
• Because of our limited ability to carry out
  multiple discriminations in parallel, only
  physical featural analyses can be carried out in
  parallel.
• Counterevidence findings of divided-attention
  studies
• People are capable of fairly extensive parallel
  processing.
• Ex. Letter search tasks

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Broadbends filter theory (1958)

• Early selection selection is based on physical
  properties of the stimulus (e.g., pitch,
  loudness)
• Only one input channel can be processed at a
  time
• Semantic interpretation only after selection
• Conscious control
• It takes time to shift attention

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When does the selection take place?

• Classic Theory II. Late Selection
• Proposed by Deutsch (1963)
• Perceptual analysis operates without capacity
  limitations and without voluntary control.
• Counterevidence
• Inattentional Blindness
• Divergence of ERPs (Event-related potentials)
  very early after presentation of a stimulus.

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Late selection
Attended Channel THE GIRL WAS dogs, six, beach
... Unattended Channel world, eight, WAITING
FOR HER ... Reported THE GIRL WAS WAITING FOR
HER ...
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Sperling (1960) partial report

• An array of letters (three rows of four) was
  flashed briefly
• In whole report, the observer recalled as many
  letters as possible, 4.
• 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
• Observers can selectively encode into memory a
  spatially defined subset of the arrayan act of
  spatial selective attention

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Spatial attention the selective processing of
information at a given location.
Posner, Nissen, Ogden (1978)
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Posner, Nissen, Ogden (1978)
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Attention plays a key role in perception

• 1980s and early 90s
• 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
• psychophysics
• single-unit recording
• neuroimaging

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Limited resources

• The high-energy cost of neuronal activity
  involved in cortical computation limits our
  ability to process information
• 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
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Selective Attention

• 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)
• Selective Attention (processing input
  preferentially) is the natural strategy for
  dealing with this bottleneck.

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Selective Visual Attention

• Capacity Limitation
• As visual information traverses the successive
  cortical areas of the ventral visual stream, the
  size of receptive fields increase.
• Neurons in higher order areas with large
  receptive fields have to deal with many visual
  stimuli that appear simultaneously within their
  receptive fields.
• This is why the neurons which make up the visual
  system are limited-capacity channels.

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Visual attention

• facilitation and selection of information
• overt attention - head and eye movements
• covert attention - monitor the environment
  
  inform eye movements

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Spatial covert attention

• sustained transient
• endogenous exogenous
• controlled reflexive
• goal-driven stimulus-driven
• 300 ms... 80 - 120 ms
• cortical also subcortical
• feedback ?

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Campbell Robson (1968)
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Contrast sensitivity function
Sensitivity (1 / Threshold)
Spatial Frequency (cpd)
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Attention enhances sensitivity

1 cpd
4 cpd
8 cpd
2 cpd
neutral
peripheral
Carrasco, Penpeci Eckstein, Vis.Res. 2000
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modified Naka-Rushton function N attentional
parameter
Martinez-Trujillo Treue 02
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Ling Carrasco, Vis. Res. 2006
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Ling Carrasco, Vis. Res. 2006
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Sustained attention adaptation
Does the enhanced signal due to sustained
attention lead to a stronger, longer-lasting
adaptation effect?
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Contrast thresholds
response cue

• Adapter 50 contrast counter-phase flicker (9
  Hz)

2AFC orientation discrimination task (3)
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Contrast threshold over time
Ling Carrasco, Nature Neurosci 2006
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Attentional effect neutral / attended
threshold
Enhancement
Impairment
Ling Carrasco, Nature Neurosci 2006
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Attention benefit and cost
Ling Carrasco, Nature Neurosci 2006
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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