Lecture 2: attention
- Attention
- The first step to understanding consciousness
- Kinds of attention
- Alerting
- Orienting
- Execution
- Mechanisms of attention
- The spotlight of attention
- Access control
the key computational concept
The unifying concept for understanding consciousness is
access
among representations.
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managing access to information
The unifying concept for understanding consciousness is
access
among representations.
Aspects of the problem:
-
The environment presents far more perceptual
information than can be effectively processed.
-
Tasks require partial information.
Aspects of the solution:
slide 6
managing access to information
The unifying concept for understanding consciousness is
access
among representations.
Aspects of the problem:
-
The environment presents far more perceptual
information than can be effectively processed.
-
Tasks require partial information.
Aspects of the solution:
Note the contraposition:
The
Aleph
············································································
The Zahir
slide 7
slide 9
slide 10
attention and executive control
The Stroop effect:
interference between color and word shape information
makes response selection more difficult in some conditions than in
others.
slide 11
attention and executive control
The Stroop effect:
interference between color and word shape information
makes response selection more difficult in some conditions than in
others.
Executive control: balancing responsiveness to the flow of
information from the senses and from memory with adherence to one's own
goals and desires.
slide 12
mechanisms of attention
The egosphere — a representational structure centered on the
self that facilitates the computational analysis of the behavioral
tasks facing an embodied agent such as a human being.
In humans, covert orienting of attention as well as the visuomotor map for
reaching appear to be framed in spherical coordinates.
Keeping visual and motor representations in spatial register makes
possible coordination of vision and motor control using spatially aligned
neural maps found in the cortex and in subcortical areas of the brain.
slide 13
covert attention effects on a V4 RF
Attentional control over the responsiveness of a V4 neuron to stimuli
within its receptive field (Moran and Desimone, 1985) —
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Microstimulation of the frontal eye fields (FEF, a cortical area
implicated in saccade generation) improves performance in a
covert spatial attention task, but only if the stimulus is
situated inside the motor field (the would-be saccade target area; Moore & Fallah, 2001).
The microstimulation current was always below the threshold needed to
evoke an actual saccade, yet it sufficed to cause the covert shift of
attention to the target location (overtly, the monkeys maintained fixation
throughout each trial).
slide 15
effects of FEF microstimulation
In a follow-up study designed to identify the neural basis of this effect,
Moore and Armstrong (2003) determined that responses of neurons in area V4 to
visual stimuli are enhanced by subthreshold stimulation of retinotopically
corresponding sites within the FEF.
Histograms show the V4 neuron's mean response during control (black) and
stimulation (red) conditions, for two time periods: after the onset of RF
(Visin) and non-RF (Visout) stimuli and after a 50-ms
subthreshold (20 uA) stimulation train had been applied to the FEF site.
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computing attention
The model of Itti, Koch, and Niebur (1998).
Visual input is first decomposed into a set of topographic feature maps.
Different spatial locations then compete for saliency within each map,
such that only locations which locally stand out from their surround can
persist.
All feature maps feed, in a purely bottom-up manner, into a master
saliency map which topographically codes for local conspicuity over
the entire visual scene.
The model's saliency map is endowed with internal dynamics which generate
attentional shifts.
slide 17
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the (rough) functional neuroanatomy of attention
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the functional neuroanatomy of attention
The functional connections among areas implementing attention in the
primate brain (Shipp, 2004), illustrating its fundamental
retinotopic architecture.
The ventral pulvinar nucleus and the superior colliculus are
subcortical areas where the control over attention is concentrated.
Legend:
- PEF/FEF, parietal/frontal eye fields
- V1-TE, visual cortical areas in the occipito-temporal processing stream
- IOR, inhibition of return
[the anti-Zahir]
slide 21
implementing access
A dynamic router circuit can be built with McCulloch-Pitts formal
neurons — idealized devices that mimic some of the key
computational characteristics of real neurons.
An M-P neuron emits a spike on its output line ("axon") if and only if the
sum of the excitation and the inhibition (positively and negatively
weighted signals) at its inputs in the preceding time interval exceeds a
fixed threshold (indicated here by the numeral inside the circle).
In this circuit, a spike emitted by the source will be routed to
destination #1 if the steering control signal is quiescent. If the control
emits a spike simultaneously with the source, the top neuron is inhibited,
but the bottom one is not, and the source spike is routed to
destination #2.
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from switched circuits to virtual computing
A neural gadget capable of steering information and of configuring and
temporarily sequestering a circuit to let the sequence of operations
it implements run their course is a primary component of the ultimate
piece of computational magic — the
virtual machine.
With this functionality, it becomes possible to decide upon the
destination of a signal on the basis of some property of the signal
itself. This, in turn, endows the system with a capacity
for conditional branching:
if condition C holds, execute subprogram P1;
otherwise, execute P2.
The subprograms themselves can be implemented by hard-wired circuits,
which receive their inputs through the dynamic gating mechanism.
If the steering signals themselves reside in working memory, they can
be modified by the outcome of earlier processing, thereby placing
control and data on an equal footing.
A computational system that can do that attains the pinnacle of
flexible learning — the capability of dynamically rewriting its own
"program" on the basis of experience.
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selective attention and the grand cover-up
The eyes move three times per second; why is it that my visual world is not
in constant flux?
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selective attention and the grand cover-up
My eyes move three times per second; why is it that my visual world is not
in constant flux?
Because it is virtual.
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The Zahir
"I am no longer the 'I' of that episode; but it is still possible for me
to remember what happened, perhaps even to tell it. I am still, however
incompletely, Borges."
"No soy el que era entonces pero aún me es dado recordar; y acaso
referir, lo ocurrido. Aún, siquiera parcialmente, soy Borges."
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The Zahir
"The determinists deny that there such a thing in the world as a single
possible act, id est an act that could or could not happen; a
coin symbolizes man's free will."
"Los deterministas niegan que haya en el mundo un solo hecho posible, id
est un hecho que pudo acontecer; una moneda simboliza nuestro libre
albedrío."
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The Zahir
"With scrupulous lack of plan..."
"Con desorden estudioso..."
[Compare the mention of "oxymoron" earlier in the story.]
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The Zahir
The "tale of fantasy" about Fafnir: an unwritten book!
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The Zahir
"...it is as though my eyesight were spherical, with the Zahir in the
centre."
"...más bien ocurre como si la visión fuera esférica y el Zahir campeara
en el centro."
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The Zahir
"According to the teaching of the Idealists, the words 'live' and
'dream' are rigorously synonymous."
"Según la doctrina idealista, los verbos vivir y soñar son
rigurosamente sinónimos."
[Note the focus on words]
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modes of visual awareness
Reflex
Phenomenal experience
Reflection
