lecture 9: attention Flashcards
why do we need attention
- Limited resources:
- Energy metabolism in the brain can support only ~0.1
spikes/sec/neuron on average. - Can perform only one action (eye movement, arm
movement, etc.) at a time. - Makes downstream processing easier:
- Ignore irrelevant neuronal signals.
- Boost reliability of the relevant signals.
- Working memory/awareness
Variations of Attention Selection:
Overt Attention Eye Movements
Most direct way to shift attention
* Poor resolution in periphery means that you are aware primarily
of things near center of gaze (fovea)
* Lots of things you can’t do without moving your eyes
Variations of Attention Selection:
Covert Attention
Hermann von Helmholtz (1894)
First described the idea of “COVERT” attention.
“COVERT” attention = attending without looking
found he could discern letters in the illuminated
part of the screen if attention was fixed there prior
to the flash of light
Spatial Attention
Effects of endogenous spatial attention (covert or overt)
endogenous
having an internal cause or origin (you decide to pay attention during lecture)
“Posner” task
The spatial cueing or Posner cueing task (Posner, 1980) is a common paradigm for studying visual attention. For the participant, the task is easy: detect when a target stimulus is presented, and respond as quickly as possible.
tests both endogenous and exogenous
exogenous attention
something outside of you is grabbing your attention, hear a loud noise and reflexively check
- Bottom-up (Exogenous)
- feature/stimulus driven
- “reflexive” or automatic
- fast
- temporary
- Top-down (Endogenous)
- goal or experience driven
- voluntary
- slower
- can be persistent
Benefit and cost of Exogenous attention:
Inhibition of Return
Exogenous or ‘reflexive’ attention to the cued location benefits detection if target occurs soon after cue, but is worse if the target occurs later
– not found with Endogenous attention
Feature Based Attention Selection:
feature integration takes longer
single feature- parallel
integration of features- serial
Object Based Attention Selection
Target detection is faster at
position B (within the cued object),
than position C (in a different
object), even though the distances
A-B, and A-C, are exactly the same.
Can’t explain this in terms of a
“spatial spotlight” effect. Hence,
“object-based attention”.
Time-Based Attention Selection
Attentional blink task
For example, imagine you’re driving your car down a busy road when you notice a car in front of you has starting to drift into the other lane. Your attention becomes briefly focused on the other car, which limits your ability to attend to other traffic for about half a second
Variations of Attention Selection:
Auditory Attention*
Dichotic listening task
A dichotic-listening task requires the subject to shadow, or repeat aloud, a message presented to one ear while ignoring a message presented to the other ear. Early work using the dichotic listening paradigm revealed that subjects were very capable of successful shadowing and successful blocking.
“cocktail party problem”
Can filter out irrelevant info and focus on
one stream at a time
distraction and somatosensory perception (pain)
buzzing bees for shots
Neurophysiology of Visual Attention
in monkeys, lateral intra-parietal area (LIP) has
both forward connections (FEF – frontal eye
field), and feedback connections (cortical, V4,
IT; subcortical, superior colliculus)
LIP
lateral intra-parietal area
LIP neurons are multimodal (vision, audition),
combining information into an overall “saliency
map” (or importance map), with higher activity in
locations that are behaviorally relevant (e.g.,
where something unexpected just happens;
where objects have the features you are looking
for). This map doesn’t include feature
information, just a spatial map of “important
locations” (or salience map), and it guides
attention and eye-movements to locations of
interest.
homologue to monkey LIP is
human Intraparietal Sulcus (IPS)
Parietal Neurons and Attention
Recordings in this area find neurons that have sensory responses (including auditory)
as well as motor responses
Visual responses in cells in the cortical visual (and auditory) areas are gated according to the behavioral significance of
the stimulus
Among the earliest evidence showing a correlation between
spatial attention and neural activity
Attention Modulates Activity of V1 & V2 Neurons
-V1 and V2 neurons respond more when attention is
directed to the location matching their receptive fields
A Ventral Visual Area for Faces (FFA)
Vs.
Places (parahippocampal place area or PPA)
Tong et al. (1998)
PPA and FFA respond to the attention/conscious perception
Attention, the parietal lobe and downstream processing:
Summary
- Neurons in the parietal lobe respond to stimuli in
attended (overt and covert) regions of visual (and auditory) space - Overlapping regions respond to attention driven
actions - Parietal-frontal attention system modulates
downstream processing in sensory cortices,
potentially boosting signal for attended stimuli
Deficits of Attention
- Hemispatial Neglect
- Balint’s syndrome
Spatial Neglect
-Following damage to dorsal pathway (parietal lobes, usually right side)
-Loss of attention or awareness to contralesional side (usually left side)
-Neglect on the left visual space, and the body (vision, audition, touch)
-Patient often denies any problem
-examples from art, bisection task, visual search, drawing
Line bisection task (multiple lines)
neglect left side of space, relative to
the patient’s body (egocentric)
egocentric
Loss of attention or awareness to left side of body/space
Visual Search
Patient searched for a “T”
-Eye movements were tracked (shown as yellow traces
how do patients with hemispatial neglect draw
How do we know this isn’t a “perception problem”?
Extinction (example with right parietal/left neglect)
allocentric
Object-based Neglect
Loss of attention or awareness to left side of OBJECT (not necessarily
space, although often correlated with left side of space)
-examples from rotated objects, word representations
Space-centered Neglect vs. Object-centered Neglect
-possibly involve different regions of brain damage
-space-centered = more dorsal regions (IPL, TPJ)
-object-centered = more ventral regions (STG)
Balint’s Syndrome
Balint syndrome sometimes referred to as Balint-Holmes syndrome, is described as a triad of optic ataxia, oculomotor apraxia, and simultagnosia. It is a rare and disabling condition usually seen with bilateral parietal lobe lesions
-Loss of attention or awareness to both sides of space
-Following damage to both parietal lobes
-Can only report seeing one object at a time (simultaneous agnosia)
-“Attentional tunnel vision”
-(rarely) voluntarily move their eyes
-Typically temporary
Normal Visual Perception
-Visual acuity
-Stereopsis (depth perception)
-Motion detection
-Object recognition
-etc.
Balint’s Syndrome
- Location-based selection
Attending to the location of an object
- Feature-based selection:
Attending to features (e.g., color, shape)
in an array of objects
- Object-based selection:
Attending to a particular object (e.g., face
vs. scene)
Attending to the face
results in FFA activity
Attending to the scene
results in PPA activity
what part of the brain is crucial for attention
In monkeys, lateral intra-parietal area (LIP) has both forward
connections (to frontal eye fields, FEF, which can direct eye
movements) and feedback connections that can impact lower
levels of the system
LIP neurons have large spatial receptive fields that respond to
input at a particular location
– If something draws attention to the receptive field (e.g., an
unexpected event or the appearance of a target you are looking
for), activity in LIP increases
human homologue is intraparietal
sulcus (IPS)
LIP computes a salience map (map of behaviorally important
parts of space), and activation in LIP can tell you where to direct
attention and eye movements
Parietal Neuron Experiments
- Measure from LIP neuron in monkeys
Monkey stares at fixation, is taught that the target visual stimulus
is a light
- If monkey ignores the light, there isn’t much activity in parietal
neuron
If monkey moves its eyes when the light comes on, much stronger
response in parietal neurons (responds even before monkey moves
its eyes)
Neuron still fires even if the monkey attends to the light without
moving eyes (responds even before monkey reaches out its hand)
intraparietal
sulcus (IPS)
(human homologue to monkey LIP) modulates activity in
area V4 (sensitive to color) and area MT (sensitive to motion)
Example: In array of moving dots, either attend to motion or to color
When attending to motion, you get a stronger response in area MT
When attending to color, you get a stronger response in V4
- Object-based Neglect:
– Damage to more ventral regions
(right STG) – closer to “what” pathway
– Loss of attention/awareness to left
side of an object
Responds to left side of space, but neglects left side of objects
(object-centered frame of reference)
Evidence from:
– Rotated objects
– Word representations
Patients have a spatial mental
representation of the object
* Trouble with access to the left
half of the object, regardless of
orientation (object-centered
frame of reference)
egocentric
spatial neglect is egocentric: (relative to
one’s body, not relative to your eye gaze)
Evidence from:
– Artist’s self-portrait
– Line bisection
– Visual search
– Copying drawings
– Number line bisection (Zorzi et al., 2002)
– Spatial neglect in imagery (Bisiach & Luzzatti, 1978)
spatial vs object based neglect
“Attentional tunnel vision”
People with balint’s syndrome Can only report seeing one object at a time
– Normal visual perception (acuity, depth perception, motion
detection, object recognition) if you direct their attention to an
object
However, their perception might depend on what they construe
as an object
How patients construe the input affects whether or not they can
attend to an object (e.g., a face vs. separate objects)
